Site icon Deep Green Permaculture

How to Graft Eggplant onto Devil Plant

Angelo (admin)
giant devil fig Solanum chrysotrichum for grafting eggplant
A variety of “Devil Plant”, giant devil’s fig (Solanum chrysotrichum), used as a rootstock for grafting eggplant.

Would you like to grow an eggplant tree — a large, established plant or small tree capable of producing a huge crop of dozens of eggplants that can continue growing from one season into the next, rather than starting again from a seedling every spring?

It can be done by grafting eggplant (Solanum melongena) shoots onto a vigorous perennial Solanum rootstock commonly referred to as a Devil Plant. The Devil Plant provides the roots and lower part of the plant, while the grafted eggplant branches produce the edible crop. Once established, the rootstock can support numerous grafted branches, allowing a single plant to carry a much larger crop than an ordinary eggplant grown from seed each year.

Devil Plants are useful as rootstocks because they are vigorous perennial shrubs or small trees with extensive root systems. An established root system occupies a much greater volume of soil than the roots of a young eggplant plant, giving it access to more water and mineral nutrients and allowing it to support considerably more growth above ground. Some Devil Plant species also provide resistance or tolerance to important soil-borne diseases and root pests that attack cultivated eggplants.

Eggplants themselves are perennial plants when temperatures remain warm enough, but in cool-temperate climates they are normally grown as annuals because winter temperatures stop their growth or kill the plants. If the grafted eggplant branches are protected through winter, they can resume growth the following spring on an already established root system and older stems rather than starting again from a small seedling. Tomatoes can also be grafted onto compatible Solanum rootstocks, making it possible to grow both eggplant and tomato branches on the same established plant.

The grafting shown in this article was carried out on giant devil’s fig (Solanum chrysotrichum), using a simple cleft or wedge graft. Another related species, devil’s fig (Solanum torvum), has a long history of use as an eggplant rootstock and has been extensively studied for resistance to soil-borne diseases. Before getting into the grafting process, it is important to identify these plants correctly, because the common name “Devil Plant” is used for several different Solanum species.

What Is a Devil Plant?

They say the devil is in the details, and with Devil Plants there are some important details to consider — namely, what exactly is a Devil Plant?

“Devil Plant” is a common name rather than the botanical name of a single species. Several prickly members of the genus Solanum have been called Devil Plant, devil’s fig or devil’s apple, and more than one of these plants has been used as a rootstock for grafting eggplants.

The species most relevant here are devil’s fig (Solanum torvum), giant devil’s fig (Solanum chrysotrichum) and devil’s apple or cockroach berry (Solanum capsicoides). All belong to the Solanaceae, or nightshade family, which also includes tomato, potato, eggplant, chilli, capsicum, tobacco, petunias and many other familiar plants.

Their botanical relationship to eggplant is what allows some of these plants to be grafted together, but belonging to the same family does not automatically make two plants graft-compatible. Even within the genus Solanum, different combinations vary in how readily they form a graft union and how well that union performs as the plant grows. The species also differ in growth rate, root development, disease resistance and longevity, so it is preferable to use a correctly identified plant with an established history of successful eggplant grafting rather than an unidentified wild Solanum that simply looks similar.

Devil’s Fig (Solanum torvum)

Devil’s fig (Solanum torvum), also commonly known as turkey berry, prickly nightshade and wild eggplant, is an erect perennial shrub or small tree that commonly grows around 0.8–3 m (2½–10 ft) high. Its native range extends from Mexico through Central America and the Caribbean into northern South America and eastern Brazil, although it has now become established throughout many tropical and subtropical regions of the world.

The plant develops a woody root system consisting of a deep taproot and numerous lateral roots spreading through the surrounding soil. This extensive root system allows an established plant to obtain water and mineral nutrients from a much larger volume of soil than a young eggplant plant, which is one of the characteristics that makes S. torvum useful as a rootstock. Its stems are green or purplish when young and become brownish as they age, while prickles may occur on the stems, leaf stalks and leaves.

The leaves can reach approximately 30 cm (12 in) long and 15 cm (6 in) wide. They are oval to shallowly lobed, generally with no more than about seven blunt lobes, and are hairy on both surfaces. The white, star-shaped flowers are up to approximately 25 mm (1 in) across and are carried in large clusters.

The fruit are spherical berries approximately 12–17 mm (½–⅔ in) in diameter. They are green when immature, change to yellowish green or yellow as they ripen, and eventually become dark as they dry. The fruit are used in traditional cuisines in parts of South-East Asia, India, Africa and the Caribbean, although glycoalkaloid levels vary considerably between S. torvum fruits, so fruit from different populations should not automatically be regarded as equally suitable for eating.

Of the plants commonly referred to as Devil Plants, S. torvum is the most thoroughly documented as a rootstock for cultivated eggplant. It is valued for vigorous growth and for resistance or tolerance to several important soil-borne problems, including bacterial wilt, fungal wilts and several root-knot nematodes. Research has also examined its ability to grow under difficult soil conditions, including saline soils.

The older version of this article described S. torvum as a short-lived perennial and stated that most plants live for about two years. Current botanical sources describe it as a perennial shrub or small tree but do not support a normal fixed lifespan of two years. The lifespan of an individual plant varies with climate, soil conditions, disease pressure and how the plant is managed.

Giant Devil’s Fig (Solanum chrysotrichum)

Giant devil’s fig (Solanum chrysotrichum) is the species shown throughout the grafting photographs in this article. It grows as a large shrub or small tree and is native from Mexico through Central America.

Australian government descriptions record plants reaching around 4 m (13 ft) high, while botanical records from Victoria and elsewhere show that plants can reach approximately 7 m (23 ft) under favourable conditions. The young stems and leaves are densely covered with reddish or rusty stellate hairs. Stellate hairs are branched hairs in which several arms radiate outward from a central point, giving each hair a star-like appearance under magnification.

The leaves are large and deeply lobed, commonly about 17–30 cm (7–12 in) long and 12–20 cm (5–8 in) wide, although leaves approximately 40 cm (16 in) long have been recorded. They usually have seven to thirteen prominent lobes and are particularly hairy on the underside.

The white, star-shaped flowers are noticeably larger than those of S. torvum, measuring approximately 30–45 mm (1¼–1¾ in) across. The round berries are about 10–15 mm (⅜–⅝ in) in diameter and ripen to yellow or orange-yellow.

Giant devil’s fig is also much more heavily armed than ordinary devil’s fig. The stems, branches, leaf stalks and major veins on the undersides of the leaves carry stout prickles, generally 3–9 mm long and broad at the base. These prickles can be straight or slightly recurved, making a mature plant rather unpleasant to handle without care.

There has been some confusion over the botanical name of giant devil’s fig. Older Australian publications sometimes referred to it as Solanum hispidum, but current botanical authorities recognise Solanum chrysotrichum as the species involved here, while S. hispidum is a separate species. VicFlora specifically records S. hispidum as a name that was misapplied to S. chrysotrichum in older Victorian botanical literature, so an older Australian reference to “giant devil’s fig (Solanum hispidum)” may actually be describing S. chrysotrichum.

Devil’s Apple (Solanum capsicoides)

Devil’s apple or cockroach berry, Solanum capsicoides, is another prickly Solanum native to tropical South America. Older references sometimes treated Solanum capsicoides and Solanum aculeatissimum as though they were the same species, and the earlier version of this article reflected that older classification.

Current botanical taxonomy recognises them as separate species. Solanum capsicoides is an annual or subshrub native to southern tropical America, while Solanum aculeatissimum is a separate shrubby species whose native range extends through southeastern and southern Brazil into south-central Paraguay.

This is a good example of why common names such as Devil Plant are not sufficient for accurate identification. If a plant is going to be maintained for several years and used to carry numerous grafts, establish which species it is before using it as a rootstock.

How to Tell Devil’s Fig and Giant Devil’s Fig Apart

Devil’s fig (Solanum torvum) and giant devil’s fig (Solanum chrysotrichum) look sufficiently similar that they can easily be confused, particularly when the plants are young. The easiest identification comes from comparing several features together, especially the leaf lobes, flower size, sepal size and the colour of the hairs on the new growth.

Devil’s fig usually has leaves 5–21 cm long with about seven shallow to moderately deep lobes. Its white flowers are comparatively small, measuring up to about 25 mm across, while the sepals are only about 3–4 mm long. The dense star-shaped hairs covering the new growth are whitish or yellowish.

Giant devil’s fig has larger leaves, usually 9–35 cm long, with seven to thirteen moderately deep to very deep lobes. Its white flowers are larger, measuring about 30–40 mm across, and the sepals are correspondingly larger at approximately 7–10 mm long. The dense star-shaped hairs on the new growth are reddish.

For a quick field identification, hair colour is especially useful. Solanum torvum has whitish or yellowish hairs on the new growth, while Solanum chrysotrichum has conspicuous reddish or rusty hairs. Giant devil’s fig also generally has more deeply lobed leaves and more prominent prickles.

The fruit provide another useful comparison. Devil’s fig produces round berries approximately 12–17 mm (½–⅔ in) across that ripen from green to yellowish green or yellow, while giant devil’s fig produces berries about 10–15 mm (⅜–⅝ in) across that ripen yellow to orange-yellow.

Interestingly, the species name chrysotrichum is derived from Greek words referring to golden hair, which is rather misleading because the hairs on fresh new growth usually appear distinctly rusty or reddish.

Why Use a Devil Plant as an Eggplant Rootstock?

Grafting joins two plants so that they grow together while each retains its own genetic identity. The plant supplying the roots is called the rootstock, while the shoot grafted onto it is called the scion.

When an eggplant scion is grafted onto a Devil Plant, the roots and any shoots growing from below the graft remain genetically those of the Devil Plant. The branch growing above the graft remains genetically the eggplant variety from which the scion was taken, so a cultivar that produces long purple eggplants before grafting will continue producing the same fruit after it has been grafted.

What changes is the root system supplying that eggplant branch. An established perennial rootstock already has roots extending through a large volume of soil, giving it access to more water and mineral nutrients than the much smaller root system of a young eggplant plant. This allows the grafted plant to produce more vegetative growth and support a heavier crop, and research comparing grafted and ungrafted eggplants has found increased plant vigour and productivity when S. torvum is used as the rootstock.

The rootstock can also provide resistance to diseases and pests that attack the roots. This is one of the main reasons vegetable crops are grafted commercially. An eggplant cultivar may produce excellent fruit but have roots that are highly susceptible to a particular soil-borne disease; grafting allows the grower to retain the desirable fruiting cultivar while replacing its susceptible root system with one that resists the disease.

That resistance comes from the rootstock and does not make the entire grafted eggplant resistant to every problem. An eggplant grafted onto S. torvum can still develop diseases that attack the foliage and stems, suffer insect damage and be injured by cold. The rootstock changes the below-ground part of the plant, affecting water and mineral uptake, root-to-shoot hormonal signalling, tolerance of difficult soil conditions and resistance to particular root pathogens.

Grafting Eggplant to Control Bacterial Wilt

One of the important agricultural reasons for grafting eggplants onto devil’s fig is the control of bacterial wilt, a serious disease of eggplant, tomato and other solanaceous crops in warm climates. The disease is caused by bacteria within the Ralstonia solanacearum species complex, which enter through the roots and colonise the xylem, the vascular tissue responsible for carrying water upward from the roots through the plant.

As the bacteria multiply, the xylem becomes obstructed and damaged, reducing the plant’s ability to move water from the roots to the leaves. The foliage then wilts even when there is adequate water in the soil because the water-conducting tissues inside the plant are no longer functioning properly.

When I originally researched this technique, I found an article published by the Queensland Department of Primary Industries titled Grafting eggfruit to control bacterial wilt. It recommended devil’s fig (Solanum torvum) as a resistant rootstock for eggplant.

The original article stated:

Suitable rootstock

A rootstock that can be used in eggfruit grafting is devil’s fig (Solanum torvum), the fruit of which is used in Indonesian and Thai cooking. Devil’s fig is quite resistant to bacterial wilt (Ralstonia solanacearum); however, it has shown wilt symptoms when planted through plastic mulch, due to the higher soil temperature under the plastic.

Other possible types of rootstock are giant devil’s fig (Solanum hispidum – beware the thorns) as well as wild tobacco tree (Solanum mauritianum). Although not included as part of the trial, these may be good options if their resistance to wilt is as good as devil’s fig. The amount of suckering from these plants is unknown. Devil’s fig tends to be more adaptable to different soils in the wild than the other two.

There are several useful practical points in that passage. Solanum torvum was the rootstock actually used and recommended on the basis of its bacterial-wilt resistance, while giant devil’s fig and wild tobacco tree were suggested as possible alternatives but had not been included in the same trial. Their resistance to bacterial wilt was therefore not demonstrated by that work in the same way as the resistance of S. torvum.

The observation about plastic mulch is also important because the resistant devil’s fig plants developed wilt symptoms where the mulch increased the soil temperature. Disease development depends on the interaction between the pathogen, the plant and the growing environment, so changing the temperature around the roots can alter how effectively the plant resists infection.

The same source noted that ordinary devil’s fig appeared more adaptable to different soils than giant devil’s fig and wild tobacco tree, and that the amount of suckering produced by those alternative rootstocks was unknown. Suckering is an important practical consideration because every vigorous rootstock shoot uses water and mineral nutrients taken up by the roots and sugars produced through photosynthesis, while also creating additional pruning work.

Subsequent research has continued to support the use of S. torvum against bacterial wilt. When susceptible eggplant or tomato scions are grafted onto S. torvum, the scions remain genetically susceptible, but the resistant root system greatly restricts development of the disease and the upward movement of bacteria into the grafted shoot.

Other Root Diseases and Root-Zone Problems

Bacterial wilt is not the only soil-borne problem for which S. torvum is useful as a rootstock. Research also describes resistance or tolerance to fungal wilts, including Verticillium wilt, as well as resistance to several important root-knot nematodes.

Root-knot nematodes are microscopic roundworms, principally within the genus Meloidogyne, that enter plant roots and establish specialised feeding sites. As the nematodes feed, the surrounding root tissues enlarge and form the swollen galls or “knots” from which these pests get their common name.

A heavily infested root system cannot absorb water and mineral nutrients efficiently because much of the normal root tissue has been damaged or distorted. Above ground, affected plants may grow poorly, wilt during warm weather and produce much smaller crops even though the soil contains adequate water and nutrients.

Cultivated eggplants generally have poor resistance to root-knot nematodes, whereas S. torvum provides useful resistance to several important species. Research on S. torvum-derived rootstocks has demonstrated resistance to isolates of Meloidogyne incognita, M. javanica and M. luci. The degree of resistance varies with the genetics of both the rootstock and the nematode population, so resistance is not identical in every combination.

Solanum torvum has also been studied under difficult soil conditions, including saline soils and soils affected by some heavy metals. More broadly, vegetable grafting is used to help plants tolerate abiotic stresses, which are stresses caused by the physical or chemical environment rather than by living pests or pathogens. These include factors such as salinity, cold root-zone temperatures and water stress.

A rootstock can therefore improve the performance of the grafted plant in several different ways. Some benefits result from direct resistance to particular pathogens, while others come from differences in root size, root distribution, water and mineral uptake, and the ability of the roots to keep functioning under difficult soil conditions.

Eggplant Grafting in Commercial Horticulture

Vegetable grafting has a surprisingly long history. Researchers Y. Huang, Q. S. Kong, F. Chen and Z. L. Bie of Huazhong Agricultural University reviewed the history of vegetable grafting in China and reported that descriptions of the practice appear in the agricultural work Fan-Sheng-Zhi-Shu, dating from the first century BCE.

Modern commercial vegetable grafting developed much later. Its use expanded rapidly in China from the 1970s as protected vegetable production increased, particularly as a way to control soil-borne diseases and improve the ability of vegetable crops to tolerate difficult growing conditions.

The authors reported that, during the period represented by their review, approximately 40% of watermelon, 20% of melon, 30% of cucumber, 15% of eggplant, 1% of tomato and 1% of pepper production in China used grafted plants. The paper was published in 2015, so these figures represent the period covered by the review rather than current 2026 production levels.

The rootstock combinations used commercially are also informative. Tomatoes were grafted onto selected tomato (Solanum lycopersicum) rootstocks, onto eggplant (Solanum melongena), and onto interspecific S. lycopersicum × S. habrochaites rootstocks. Eggplants were grafted onto selected eggplant rootstocks and Solanum torvum, while peppers were grafted onto selected Capsicum annuum rootstocks.

Grafting therefore does not necessarily involve joining two different species. A desirable crop variety can be grafted onto another selection of the same species when that rootstock has more vigorous roots or useful resistance traits, while wild relatives such as S. torvum are used when they provide characteristics that cultivated eggplant does not possess.

The Chinese review describes cleft, splice and tube grafting among the methods used for solanaceous crops. For a home gardener grafting individual branches onto an established Devil Plant, the cleft or wedge graft is especially useful because the rootstock branch can be somewhat thicker than the eggplant scion and the two stems do not need to match exactly in diameter.

Why Create an Eggplant Tree in a Cooler Climate?

For home gardeners in cool-temperate climates, keeping an established eggplant plant from one growing season into the next can be just as useful as the disease resistance provided by the rootstock. Eggplants are commonly treated as annual vegetables in temperate climates, but botanically they are perennial plants; they are grown as annuals because cold weather ends their useful growing season rather than because the plant naturally completes its life cycle after one summer.

This makes a substantial difference in southern Australia. An eggplant raised from seed in spring has to develop its root system, stems and foliage before it is large enough to support a heavy crop, so a considerable part of summer can pass while the plant is still building the growth needed for fruit production.

By the time the first substantial crop develops, the warm part of the growing season may already be running out. As temperatures fall, vegetative growth slows, flowering declines and fruit takes progressively longer to develop, leaving the plant capable of producing more but without enough warm weather remaining to do so.

A grafted plant that survives winter begins the following spring with its established roots and older stems already in place. When warm weather returns, the grafted branches can resume active growth rather than spending another large part of the season rebuilding the plant from a small seedling.

In my own experience, grafted eggplants can produce for around eight months of the year under suitable conditions and remain productive for two or three years. I have also seen outdoor eggplants grafted onto Devil Plants survive a Melbourne winter and fruit again in their second year.

The perennial rootstock does not make the grafted eggplant frost-hardy because the branches above the graft remain eggplant tissue and retain the cold sensitivity of eggplant. The rootstock may survive conditions that damage or kill the grafted shoots above it, so the eggplant branches need protection if they are expected to survive into the following growing season.

A greenhouse provides the most reliable winter protection because it excludes frost and raises daytime temperatures, although sheltered positions and temporary winter structures can also be used in milder climates. Plant size becomes an important practical consideration because a modestly sized grafted plant is relatively easy to cover, while a 3 m (10 ft) plant with branches spreading in many directions is much more difficult to protect.

Choosing a Rootstock

The various plants referred to as Devil Plants do not all have the same amount of research behind their use as eggplant rootstocks. Solanum torvum has by far the strongest research and commercial history, with its compatibility with cultivated eggplant, vigorous growth and resistance to bacterial wilt, fungal wilts and several root-knot nematodes all well established.

Where disease resistance is the main reason for grafting, S. torvum is therefore the best documented choice. Giant devil’s fig, S. chrysotrichum, is the species I have used successfully for the grafts shown in this article, and an established plant develops into a vigorous perennial shrub or small tree capable of carrying numerous grafted branches.

Older Queensland horticultural material also suggested giant devil’s fig as a possible rootstock, although it has not been studied as extensively as S. torvum for specific diseases. The successful grafts shown here demonstrate that S. chrysotrichum is compatible with eggplant, but disease-resistance results established for S. torvum should not simply be transferred to another species.

Kangaroo Apple (Solanum aviculare)

For Australian and New Zealand gardeners who would prefer to experiment with a native species, kangaroo apple (Solanum aviculare) is another possible rootstock. The species is native from eastern Queensland through New South Wales and Victoria, as well as New Zealand, Lord Howe Island, Norfolk Island, the Kermadec Islands and the Chatham Islands.

Kangaroo apple is a fast-growing woody shrub and is considerably easier to handle than heavily prickled giant devil’s fig. Australian horticultural practice has included its use as an eggplant rootstock, although there is much less controlled research behind this use than there is for S. torvum, so it should not be assumed to provide the same documented disease resistance.

The species is generally a comparatively short-lived shrub rather than a long-lived tree. The older article gave a lifespan of around five to six years in favourable conditions, although longevity varies considerably with growing conditions rather than following a fixed lifespan.

The fruit also require caution. They become orange-red as they ripen and have a history of traditional use when fully ripe, but green fruit and the vegetative parts of the plant contain steroidal alkaloids and should not be eaten.

Wild Tobacco Tree (Solanum mauritianum)

Wild tobacco tree (Solanum mauritianum) is another perennial Solanum that has been used or suggested as a rootstock. It is also known as tobacco bush, tobacco weed, woolly nightshade, flannel weed, bugweed, kerosene plant and several other regional names.

It grows as a large shrub or small tree, commonly around 4–6 m (13–20 ft) high, with large grey-green leaves densely covered in soft stellate hairs. The foliage has a distinctive smell when crushed, which is reflected in common names such as kerosene plant.

Its native range extends through southeastern and southern Brazil into Uruguay and northeastern Argentina. It has become established well beyond that range, including in Australia, New Zealand, the Azores, Cook Islands, Fiji, Hawaii, India, Madagascar, Mauritius, New Caledonia, Norfolk Island, Réunion, Sri Lanka, Tonga and numerous parts of southern and eastern Africa.

The older Queensland eggplant-grafting material mentioned wild tobacco tree as a possible alternative to S. torvum, but it clearly stated that wild tobacco tree had not been included in the bacterial-wilt trial. It therefore has horticultural precedent as a possible rootstock, but the bacterial-wilt resistance demonstrated for S. torvum should not automatically be attributed to it.

Botanical literature also records S. mauritianum being cultivated in New Zealand as a rootstock for tamarillo, Solanum betaceum, providing another example of its use as a woody rootstock within the Solanaceae family.

Do Not Use Random Wild Solanums

There are hundreds of species in the genus Solanum, and many prickly species can look superficially similar. Simply belonging to the same genus as eggplant does not prove that a plant will form a durable graft union, provide useful disease resistance or be suitable for maintaining in a garden for several years.

A useful rootstock needs to be correctly identified, compatible with the scion and capable of providing a useful characteristic, such as vigorous growth, resistance to a particular root disease, tolerance of difficult soil conditions or the ability to remain established for several growing seasons. Use species with a documented or well-established history of successful grafting rather than selecting random wild nightshades.

Working With Giant Devil’s Fig

It is called a Devil Plant because it really can be a “devil of a plant” to work with if you are not careful! The stems and branches carry stout, broad-based prickles, and these also occur on the leaf stalks and along the main veins on the undersides of the leaves.

Spines on the stem of giant devil’s fig.
Spines on the branches of giant devil’s fig.
There are spines on the leaves too — that’s why it’s called a “Devil Plant”!

When selecting a branch for grafting, I remove the prickles around the point where I intend to work. There is no horticultural advantage in leaving them there, and trying to hold a branch steady while a large prickle is pressing into a finger makes accurate knife work unnecessarily difficult.

The reason for putting up with such an inconvenient plant is what it can do once established. A mature rootstock has already developed a large root system and numerous branches, allowing many eggplant scions to be grafted onto the same plant while the rootstock remains established for several growing seasons.

Propagating More Devil Plant Rootstocks

An established Devil Plant can also provide material for propagating additional rootstocks. Suitable stems removed during pruning can be used as cuttings and rooted in a propagation medium, while some Solanum species also form roots readily in water, allowing one established plant to become a continuing source of future rootstocks rather than raising every plant from seed.

This is particularly useful with S. torvum. Although the species can be grown from seed, germination can be slow, irregular and erratic, and young seedlings can take considerable time to reach grafting size. This complicates commercial nursery production because the rootstock and eggplant scion plants need to reach a suitable size for grafting at approximately the same time.

Research has therefore examined vegetative propagation of S. torvum. In a two-year nursery and field study, unrooted S. torvum cuttings were grafted with eggplant while the cuttings were simultaneously allowed to form roots. The cuttings rooted successfully while the grafts healed, substantially reducing propagation time, and the resulting plants performed similarly in the field to plants produced by conventional grafting onto already-rooted rootstocks. The same study also confirmed increased vigour and productivity in eggplants grafted onto S. torvum.

For the home gardener, there is no need to combine rooting and grafting in this way. The simpler method is to root the Devil Plant cutting first, allow it to establish a good root system and begin growing strongly, and then graft eggplant onto it.

Grafting Basics

Before starting the graft, it helps to understand what has to happen inside the stem for the rootstock and scion to grow together. Once the process is clear, the reasons for making smooth cuts, aligning the stems accurately, removing large leaves, wrapping the graft and keeping the scion humid become much easier to understand.

What Is Grafting?

Grafting is the horticultural practice of joining living tissues from two compatible plants so that those tissues heal together and the two parts continue growing as one functioning plant. The rooted lower plant is called the rootstock, or simply the stock, while the detached shoot attached to it is called the scion, pronounced “sigh-on”. In this case, the Devil Plant is the rootstock and the eggplant shoot is the scion.

For the graft to function, the internal transport tissues of the two plants must reconnect across the cut surfaces. Water and dissolved mineral nutrients move upward through xylem, the water-conducting tissue of the stem, while sugars and other organic compounds produced in the leaves are transported through phloem to other parts of the plant.

As the graft heals, new xylem and phloem develop across the graft union, reconnecting these transport systems so that the rootstock can supply water and minerals to the eggplant scion and the grafted shoot can exchange sugars and other compounds with the rest of the plant. The rootstock and scion have now grown together physically, but they remain genetically distinct: the roots retain the characteristics of the rootstock, while the shoots and fruit retain the characteristics of the eggplant scion.

What Is the Cambium and Why Does It Matter?

A successful graft depends on bringing living tissues of the rootstock and scion into close contact. In practical grafting descriptions, the cambium is often described as the thin green layer just beneath the bark, between the bark and the wood. More precisely, the vascular cambium is a very thin layer of actively dividing cells located between the phloem toward the outside of the stem and the xylem, or wood, toward the inside.

As a woody stem increases in diameter, the vascular cambium produces new xylem toward the inside and new phloem toward the outside. When a stem is cut, living cells around the wound begin dividing and forming callus, which is new tissue that develops across and between wounded surfaces.

When compatible cut surfaces from the rootstock and scion are held firmly together, callus develops across the join and new vascular tissues form through it, eventually reconnecting the xylem and phloem of the two plants. This is why cambium alignment is so important when making the graft.

If the rootstock and scion are approximately the same diameter, their outer surfaces can be aligned on both sides. If the rootstock is wider than the scion, the smaller scion should be moved toward one side so that its cambial region meets the cambial region of the rootstock there. Centring a narrow scion inside a much wider rootstock can leave the cambium separated on both sides even though the graft looks neat from the outside.

One accurately aligned side is enough for a cleft graft to heal successfully, and university extension grafting guidance specifically recommends matching the cambium on one side when the stock and scion differ in diameter. The quality of the cut surfaces matters just as much: a sharp blade produces smooth, flat surfaces that can sit closely together, while a blunt blade crushes and tears the tissues and reduces the area where the two plants can make close contact.

Why the Scion Must Be Protected From Drying

A newly cut scion has no roots supplying it with water, but its leaves and stem continue losing water through transpiration. Until new xylem has formed across the graft union, the rootstock cannot replace that water at the normal rate, so a scion that loses water too quickly will wilt and die before the graft has time to heal.

This is why most of the large leaves are removed before grafting. Reducing the leaf area reduces transpiration and therefore lowers the amount of water the scion loses while its connection to the rootstock is still developing.

The graft union is also wrapped and the scion enclosed in humid air. Wrapping prevents the exposed cut surfaces from drying and holds the rootstock and scion firmly in position while new tissue forms between them, while the high humidity around the scion greatly reduces water loss from the remaining leaves.

Commercial vegetable propagators use healing chambers for the same reason. Oklahoma State University Extension describes covered structures maintained close to 100% relative humidity with reduced light so that transpiration remains very low while the graft develops, with newly grafted vegetables remaining under these conditions for several days and, where necessary, for up to about eight days.

The graft can begin moving enough water to keep the scion alive before the new tissues have become physically strong enough to support the branch. This is why the humidity enclosure can usually be removed before the grafting tape.

The Wedge or Cleft Graft

The technique used here is a wedge graft or cleft graft, sometimes simply called a “V” graft.

To make a cleft graft, the lower end of the scion is cut into a long wedge, while the rootstock branch is cut straight across and then split vertically through the centre. The wedge-shaped scion is pushed into this cleft so that the cambial tissues of the two plants line up, after which the graft is wrapped firmly to prevent movement and moisture loss.

A major advantage of this method is that the rootstock can be somewhat thicker than the scion. A splice graft works best when the two stems are very similar in diameter, whereas a cleft graft allows a smaller scion to be positioned against one side of a larger rootstock while still bringing the cambial tissues into contact. This makes it particularly useful when grafting onto an established Devil Plant, where the available branches can vary considerably in thickness.

How to Graft Eggplant onto Devil Plant

Step 1. Gather the Required Materials

You do not need expensive specialist equipment to make this graft. For the method shown here, you will need a healthy Devil Plant rootstock and an eggplant plant large enough to provide suitable scion material, together with a sharp grafting knife, small craft knife or grafting tool; clean secateurs; grafting tape or a strip cut from a sturdy plastic bag; a small clear plastic bag; a wire or twist tie; a small piece of shade cloth; and a clothes peg or similar clip.

The tools and materials used for grafting.

A dedicated grafting knife is useful but not essential. A small inexpensive craft knife with replaceable snap-off blades works extremely well because a fresh blade is very sharp and cuts cleanly through the relatively soft stems used for this type of graft.

Whatever cutting tool is used, make sure the blade is sharp and clean. A blunt blade crushes and tears the stem instead of slicing cleanly through it, leaving irregular surfaces where the rootstock and scion need to make close contact. Cleaning the blade also reduces the chance of transferring plant pathogens from one plant to another.

Step 2. Select the Eggplant Scion

Choose a healthy, actively growing shoot from the eggplant cultivar you want to graft. A firm young shoot is preferable to extremely soft new growth or old, hardened stem tissue because it is mature enough to handle without collapsing while still being soft enough to cut cleanly.

Using clean secateurs, cut a shoot tip or suitable side branch approximately 5–10 cm (2–4 in) long.

Using sharp secateurs, cut a healthy length of eggplant stem
An eggplant shoot cut and ready to be prepared as a scion.

Prepare and graft the scion reasonably soon after cutting it. Once separated from the parent plant, it no longer has roots supplying it with water, but its leaves and stem continue losing water to the surrounding air.

Step 3. Remove the Large Leaves

Remove the large leaves from the scion, leaving the small developing leaves and buds near the growing tip.

A freshly cut eggplant stem cutting with large leaves removed, ready for grafting onto rootstock.

Large leaves lose water through transpiration over a much greater surface area than small leaves. Until new xylem forms across the graft union, the rootstock cannot replace that water at the normal rate, so removing most of the leaf area greatly reduces the amount of water the scion loses while the graft is healing.

Keep the small leaves and buds at the tip because these contain the active growing points. Once the graft begins functioning, expansion of these buds and leaves is one of the clearest signs that the graft has taken.

Step 4. Cut the Wedge on the Scion

Prepare the base of the scion by making two long sloping cuts that meet to form a narrow V-shaped wedge.

A grafting knife and an automatic grafting tool used for making the grafting cuts

Hold the scion firmly and make one long, smooth, sloping cut along one side of its base, then turn the scion over and make a corresponding cut on the opposite side. The completed wedge should be approximately 2.5–3 cm (1–1¼ in) long.

Make each face of the wedge with a single smooth slicing movement wherever possible. Repeatedly shaving or sawing at the stem leaves an uneven surface and damages more tissue, while smooth, flat cut faces fit more closely against the corresponding surfaces inside the rootstock and provide a larger area over which the graft can heal.

Avoid touching the freshly cut surfaces unnecessarily with your fingers. Keep them clean, moist and undamaged until the scion is inserted into the rootstock.

Completed eggplant scion with its V-shaped or wedge-shaped base.

Step 5. What About Specialised Grafting Tools?

A specialised grafting tool is not necessary, but there is a practical reason these tools exist: they make precise, repeatable cuts very quickly. Some use a V-shaped blade, while others make an omega-shaped or “keyhole” cut that produces complementary shapes in the rootstock and scion.

Close-up of the base of an eggplant stem cutting showing the end prepared with an omega grafting tool, producing a precise interlocking omega cut for grafting.

When the two pieces are joined, the matching cuts interlock rather like two pieces of a jigsaw puzzle. This helps keep the rootstock and scion aligned and reduces the tendency for them to slide apart while the graft is being wrapped, which is particularly useful when many grafts are being made.

When the original version of this article was written, a dedicated grafting tool could cost close to the $100 mark. Prices vary greatly now, but the basic point has not changed: these tools are a convenience rather than a necessity, and a sharp knife with a carefully made cleft graft is entirely adequate for home use.

Step 6. Select and Prepare the Rootstock Branch

Choose a healthy branch on the Devil Plant, preferably one with actively growing wood rather than very old, hard wood. A branch approximately the same diameter as the scion, or somewhat thicker, is ideal because it is easy to cut while still providing enough material to hold the scion firmly.

Using secateurs, cut the branch cleanly across at the point where you want the new eggplant shoot to grow. If you are working with giant devil’s fig, remove the prickles immediately around the grafting area before proceeding, because trying to make precise knife cuts while a large prickle is pressing into your fingers makes the work unnecessarily difficult.

Remove any leaves growing immediately around the grafting point as well. This gives clear access to the stem for making the cleft and for wrapping the completed graft.

Step 7. Make the Cleft in the Rootstock

Using the grafting knife, make a straight vertical split down through the centre of the cut end of the rootstock. The cleft should be approximately 2.5–3 cm (1–1¼ in) deep so that it closely matches the length of the wedge cut on the scion.

Cutting the cleft into the rootstock with a grafting knife.

Keep the split as straight and clean as possible so the two sides of the rootstock can fit closely against the wedge-shaped scion. Making the cut substantially deeper than the scion wedge serves no useful purpose and simply creates more wounded tissue that the plant then has to repair.

Step 8. Insert the Scion and Align the Cambium

Insert the wedge-shaped end of the eggplant scion into the cleft and push it down until most of the cut wedge is enclosed by the rootstock and the cut surfaces fit closely together.

Scion inserted into rootstock with cambium edges aligned.

If the rootstock and scion are approximately the same diameter, line up their outer surfaces on both sides so the cambial tissues meet around as much of the graft as possible. If the rootstock is thicker than the scion, do not centre the smaller scion merely to make the graft look symmetrical; move it toward one side so that its cambium sits directly against the cambium of the rootstock on that side.

One side with good cambium contact is sufficient for a cleft graft to heal successfully. Centring a narrow scion inside a much wider rootstock can leave the cambium separated on both sides even though the graft appears neatly centred from the outside.

Step 9. What If the Rootstock Is Too Hard or Woody?

Older Devil Plant branches can become too hard to spread easily after the cleft has been cut. When this happens, cut a very narrow wedge from the centre of the rootstock, making the opening narrower than the wedge on the scion.

Insert the grafting knife into this narrow opening and gently lever the two sides of the rootstock apart while pushing the scion into position. Once the scion has been inserted, withdraw the knife and allow the sides of the rootstock to close back around the scion, where their natural spring pressure helps hold the cut surfaces firmly together.

Do not remove a piece of rootstock as wide as the scion itself. If the opening is too large, the rootstock loses the spring pressure that helps clamp the scion in place and maintain close contact between the cut surfaces.

Step 10. Bind the Graft

Once the scion is correctly aligned, secure the graft firmly with grafting tape. Start below the graft and wrap upward, covering the entire cut area and extending slightly onto both the rootstock and the scion.

Graft joint is wrapped with grafting tape to hold it securely in place.

The wrapping performs two important functions. It holds the rootstock and scion firmly in position while callus and new vascular tissue develop across the join, preventing movement that could tear or disrupt these newly forming tissues, and it seals the exposed cut surfaces against moisture loss.

Wrap firmly enough to keep the two pieces in close contact and form a good moisture seal, but not so tightly that the soft stems are crushed.

Step 11. Making Grafting Tape From a Plastic Bag

Commercial grafting tape is convenient but not essential. I have obtained the same success rate using strips cut from a sturdy plastic bag as I have using proper grafting tape.

I make the strips approximately 1.5 cm (⅝ in) wide and around 50 cm (20 in) long. Because an ordinary plastic bag consists of two layers joined along the sides, cutting a strip across a bag approximately 25 cm (10 in) wide initially produces a loop; cut through one side of that loop and open it out, and the result is a strip approximately 50 cm long.

The plastic stretches slightly as it is wrapped, allowing the graft to be pulled together firmly while sealing the cut surfaces against moisture loss. Unlike some specialised grafting tapes, however, ordinary plastic does not necessarily continue stretching as the stem expands and does not automatically break down, so it needs to be checked and removed later before it begins constricting the growing stem.

Step 12. Cover the Graft With a Plastic Bag

After the graft has been wrapped, the scion is still highly vulnerable to drying because the new xylem connection between the rootstock and scion has not yet formed. Cover the entire scion with a small clear plastic bag and tie the bottom of the bag around the rootstock branch below the graft using a wire tie, twist tie or similar fastener.

Grafting scion covered with plastic bag to maintain humidity and prevent moisture loss.

The air inside the sealed bag quickly becomes humid, greatly reducing water loss from the remaining leaves and giving the graft time to form new vascular connections before the scion dries out. I add a few drops of water to the bottom of the bag to help maintain this humidity; only a small amount is needed because the purpose is to humidify the enclosed air, not to soak the graft or have liquid water running over the cut surfaces.

Before tying the bag closed, trap some air inside it so the bag remains slightly inflated rather than collapsing directly onto the leaves and scion. I have also found it useful to tie one upper corner of the bag to a higher branch so that the bag is supported from above instead of hanging its weight directly from the newly grafted shoot. These small details reduce physical stress on a graft that is still very weak and make the humidity enclosure much easier to manage.

Step 13. Shade the Plastic Bag

The clear plastic bag creates the high humidity needed to prevent the scion drying, but it can create another problem if it is exposed to direct summer sunlight. Solar radiation passes through the clear plastic and heats the air and plant surfaces inside, creating a miniature greenhouse around the scion in which the temperature can rise rapidly.

A graft that has been successfully protected from drying can therefore still be damaged or killed by excessive heat. If the plant is inside a shaded greenhouse, the graft may already receive enough protection, but if the bag is exposed to direct sun it needs to be shaded.

Some growers place a small brown paper bag over the clear plastic bag. My preference is to use a small piece of shade cloth because it reduces direct solar heating while still allowing some diffuse light to reach the scion.

Grafted scion protected from heat stress with a plastic bag and shade cloth covering — a critical step to prevent wilting while the graft union establishes

Fold the shade cloth around the plastic bag and hold it in place with a clothes peg. If several grafts have been made on the same plant, it may be easier to suspend one larger piece of shade cloth over that part of the plant rather than shading every bag individually. During this first stage of healing, the scion needs very high humidity, protection from excessive heat, minimal water loss and complete stability at the graft union.

Step 14. Allow the Graft to Heal

Once the graft has been assembled and protected, living cells around the cut surfaces begin dividing and producing callus tissue. Where the rootstock and scion have been held in close contact, this callus develops across the join and new xylem and phloem begin forming through it.

As the xylem reconnects, the rootstock progressively regains the ability to supply water to the scion. Phloem connections also form, restoring the movement of sugars and other organic compounds through the graft until the rootstock and scion are functioning as a connected plant.

Under my summer growing conditions, I have generally found that the plastic bag can be removed after approximately one week. This is consistent with standard vegetable-grafting practice, where newly grafted plants are kept under high-humidity healing conditions for several days and, where necessary, for up to about eight days while the graft develops.

The exact healing time varies with temperature, humidity, rootstock vigour, scion condition and the quality of the graft, so the condition of the scion is a better guide than simply counting days. A successful graft should remain firm rather than shrivelling, and the small leaves or buds should begin showing renewed growth as the connection with the rootstock becomes functional.

Step 15. Acclimatise the Scion to Normal Humidity

A newly healed graft can have enough new xylem to keep the scion alive while it is still accustomed to the almost saturated air inside the plastic bag. Moving it suddenly from that humid environment into hot, dry air can cause water loss from the leaves to increase faster than the developing graft can replace it, resulting in wilting.

In mild, humid weather, the bag can often be removed without difficulty. In hotter or drier conditions, reduce the humidity gradually by opening the bag slightly at first so that outside air begins mixing with the humid air around the scion, then progressively increasing the opening.

If the scion remains firm, the bag can be removed completely. If it wilts severely when the humidity is reduced, close the bag again and allow more healing time. As more xylem develops across the graft, the rootstock becomes increasingly able to replace the water being lost from the leaves.

Step 16. Leave the Graft Bound Until It Is Mechanically Strong

The humidity bag and the grafting tape perform different functions, so they do not need to be removed at the same time. The plastic bag can be removed once enough xylem has developed for the rootstock to keep the scion supplied with water under normal conditions, but the graft union can still be physically weak at this stage.

Callus and new vascular tissue continue developing and thickening after the scion has started receiving water again, so leave the wrapping in place until the graft has produced substantial new growth and the join is strong enough to support the branch. This generally takes longer than the initial vascular healing and may require several weeks.

If specialised grafting tape is used, follow the manufacturer’s instructions because some materials stretch as the stem expands or deteriorate naturally. If ordinary plastic strips are used, inspect them regularly and do not leave them tightly wrapped around the stem for months.

As the graft increases in diameter, non-stretching plastic can cut into the bark and compress the phloem and other tissues beneath it. If this continues, the plastic can girdle the stem and interfere with the movement of sugars through the plant, so once the union is strong, carefully cut and remove the wrapping without damaging the bark.

Successful grafts can begin producing vigorous new shoots quite rapidly under warm conditions, followed by flowers and fruit.

Managing the Eggplant Tree After Grafting

Once the grafts have taken, the Devil Plant rootstock will continue trying to produce its own shoots below the grafts. Any shoot emerging below an eggplant graft belongs genetically to the rootstock, and if these shoots are allowed to develop into large branches they compete with the eggplant grafts for light and space while also using water and mineral nutrients taken up by the roots and sugars produced through photosynthesis.

Remove unwanted rootstock shoots regularly while they are still small, which is much easier than allowing them to become established branches and removing them later. A few rootstock leaves on lower branches are not necessarily a problem, particularly while newly grafted eggplant shoots are becoming established, because those leaves carry out photosynthesis and contribute sugars to the connected plant.

What should be avoided is allowing a substantial ungrafted Devil Plant canopy to develop and produce its own flowers and fruit while the plant is supposed to be supporting eggplant production. If the aim is to create an eggplant tree, the major branches forming the upper part of the plant should progressively be grafted.

This is particularly relevant to S. torvum, which can produce vigorous shoots from lower buds. Commercial experience has shown that removing rootstock suckers can become a significant maintenance task when they are allowed to develop freely.

Supporting a Large Grafted Plant

A vigorous grafted eggplant can eventually carry a much heavier crop than an ordinary young plant, and that additional fruit places considerable weight on the branches. Several large eggplants growing on a single branch can apply substantial leverage to the graft union, while wind increases that force further.

A graft can therefore heal successfully and still break later if the developing union or branch is carrying more weight than it can support. Support heavily laden branches with stakes, ties, trellis wires or another suitable structure, particularly during the first season while the graft union is still thickening and producing stronger woody tissue.

Commercial guidance for grafted eggplant also recommends trellising where plants have a tendency to lodge or spread along the ground. The same need for support becomes even greater with a large plant carrying numerous grafted branches and a heavy crop.

Grafting Several Eggplant Varieties onto One Plant

An established Devil Plant does not have to carry only one eggplant variety. Different branches can be grafted with different cultivars, allowing one branch to produce long Asian eggplants, another large oval purple fruit, another white eggplants, and another striped or small-fruited varieties.

Each grafted branch continues producing the fruit of the eggplant cultivar from which that scion came. All of the branches share the same root system, but the rootstock does not alter the genetic identity of the different eggplant cultivars.

The principle is similar to a multi-grafted apple, citrus or stone-fruit tree carrying several cultivars. For gardeners with limited space, this provides a way to maintain several eggplant varieties on one established root system, while also making it possible to compare how different cultivars grow and crop when they are all supplied by the same rootstock.

Can Tomatoes Be Grafted onto the Same Plant?

Tomatoes can also be grafted onto compatible Solanum rootstocks. Commercial tomato grafting more commonly uses selected tomato rootstocks or interspecific tomato rootstocks, but S. torvum and other related species have also been investigated where resistance to bacterial wilt is required.

Studies using susceptible tomato and eggplant scions grafted onto S. torvum have shown that the resistant rootstock can greatly reduce bacterial wilt even though the tomato or eggplant scion itself remains genetically susceptible. This makes it possible to experiment with both eggplant and tomato grafts on the same compatible perennial rootstock.

I have done exactly this, adding two cherry tomato grafts to the same Devil Plant carrying eggplant grafts, and both grafts took successfully. Different crops and cultivars can grow at different rates, so pruning and training may be required to prevent one particularly vigorous graft from taking over most of the available space.

Overwintering a Grafted Eggplant Tree

In a cool climate, making the graft is often easier than keeping the grafted eggplant branches alive through winter. A perennial Devil Plant rootstock may tolerate conditions that cultivated eggplant cannot, but the shoots above the graft remain eggplant tissue and do not acquire the cold tolerance of the rootstock simply because the two plants have been joined.

In climates with frost or prolonged periods of low temperature, the grafted eggplant branches therefore need protection if they are expected to survive until the following spring. A greenhouse provides the simplest and most reliable protection because it excludes frost and raises daytime temperatures, while in milder climates an outdoor plant can also be protected using a temporary enclosure.

Position makes a substantial difference. A sheltered site protected from cold winds and receiving winter sun will remain warmer than an exposed position, improving the chances of keeping the eggplant branches alive.

Plant size also determines how difficult winter protection becomes. A moderately sized, well-trained eggplant tree is relatively easy to cover, whereas a very large plant with widely spreading branches is much harder to protect, providing a practical reason to prune and manage its size rather than simply allowing it to grow as large as possible.

A Few Afterthoughts…

All the grafting pictured in this article was carried out in mid-summer because that was when my eggplant seedlings had become large enough to provide suitable scions. I carried out about a dozen eggplant grafts on the one Devil Plant, and they all took successfully.

The biology behind grafting can sound complicated when it is explained in detail, but the actual procedure is quite straightforward once the reasons behind each step are understood. Make clean cuts, bring the living tissues of the rootstock and scion into close contact, hold the two pieces firmly together, prevent the scion from drying out and give the graft enough time to heal without being disturbed.

Tomato can also be grafted onto Devil Plant, making it possible to have tomatoes and eggplants growing on different branches of the same rootstock. I added two cherry tomato grafts to mine, and they worked too. There is nothing like experimenting to see what works.

The main practical challenge here in Melbourne is protecting the grafted plant through winter, particularly once it becomes large. I have seen tomatoes grafted onto Devil Plants in greenhouses fruiting for almost the whole year, and I have seen outdoor eggplants grafted onto Devil Plants survive a Melbourne winter and fruit again in their second year.

For gardeners in climates where ordinary eggplants spend much of summer simply becoming large enough to crop heavily, keeping an established plant from one growing season into the next can make a substantial difference. Instead of starting again each spring with a small seedling, the plant begins the season with established roots and branches already in place, allowing it to resume growth and fruit production much sooner.

That can completely change the way eggplants are grown.

References

… and one final thought on perspective, ethnocentrism and respect for other people’s cultures

I have updated the content on this article and in response to previous comments, have added this section.

To those thinking about posting about the ‘weed’ potential of the devil fig, please note THIS IS AN INTERNATIONAL WEBSITE (with the majority of readers outside Australia!), please be mindful that what plants may be indigenous or native to your area may be a ‘weed’ elsewhere, it works both ways. For some readers this is a discussion of their native plants, plants that form part of their native cuisine or traditional medicine. Grafting eggplants onto devil plants is a commercial agricultural practice in China, and a common practice amongst European gardeners, as well as ethnic gardeners of Southern European origin who live in Australia. Learn to respect other people’s cultures!

Your native plants are someone else’s ‘weeds’ too! A ‘weed’ is not a scientific or biological category or class of plant, it’s a value judgement statement based on human preference – it’s a plant growing where the observer doesn’t like it growing. If we were to write ‘weed warnings’ based on every geographical location’s perspective, EVERY PLANT WOULD HAVE A WEED WARNING!

As responsible gardeners, and mature adults able to make informed and responsible decisions, it is common sense that if plants have the potential to escape from your garden, IT IS YOUR RESPONSIBILITY to contain them, and comply with any legalities of your area!

Secondly, if you’re grafting these solanum rootstocks, all branches SHOULD BE GRAFTED! There shouldn’t be branches producing the rootstock flowers and fruit, you don’t want the plant’s energy going into something you don’t eat, they should be producing eggplants. It’s OK to have some rootstock leaves on the lower branches though.

Exit mobile version