The “Devil Plant” – Solanum capsicoides
About the Devil Plant
The Devil Plant (Solanum capsicoides), also known as a cockroach berry or soda apple, is a native of South America and grows as a perennial bush or small tree up to 3m high. It’s a member of the Solanaceae (nightshade) family of plants, which also includes tomato, potato, eggplant, chilli peppers, capsicum, tobacco, petunias and many others.
It’s called a Devil Plant because it really is a “devil of a plant” to work with if you’re not careful! The stems, branches and the main veins on the underside of the leaves have stout, broad based, hooked spines (see pictures below)
Spines on stem
Spines on branches
Spines on leaves too – that’s why it’s a “Devil plant”!
The Devil Plant flowers and produces its own fruit, which look like tiny tomatoes, and these turns red when ripe, but these are not edible to humans, but are eaten by numerous birds and animals.
Our interest in the Devil plant (Solanum capsicoides) however, is to use it as a rootstock to graft eggplants (Solanum melongena) on to. This is a popular practice with Europeans, including the ones living in Australia. Grafting creates an “eggplant tree” which can literally produce from dozens to hundreds of eggplants according to many accounts I have heard. The only necessity is to cover the grafted tree in winter so the eggplant grafts don’t die off. The process is relatively simple, you just use basic cleft “V” grafts, and the bits you cut off the Devil plant can be used for striking cuttings to grow new Devil plant, and you can either root the cuttings in water, or in potting mix.
In the southern states of Australia, where the climate is classed as “Cold”, the biggest problem with growing eggplants from seedlings is that the growing season is not long enough. They take most of Summer to produce their first crop, then it gets too cold, and no successive crops are produced. By grafting to create an “eggplant tree”, you can produce eggplants for about eight months of the year for two or three years.
Now that we’re familiar with the plant, lets get grafting!
Before I go into describing the process of grafting eggplant onto the Devil plant, it’s probably a good idea to quickly cover some basic horticultural concepts.
What is Grafting?
Grafting is the practice of joining the living tissue from one plant to that of another plant that is either the same species or closely related, so that they will fuse together to form a single plant.
There are many grafting techniques, and here we will learn how to perform a Wedge or Cleft graft, sometimes referred to as a “V” graft. It’s one of the simplest grafts, it has a very high success rate and can be done with very basic tools.
Wedge or Cleft Graft
In grafting, the plant that you are grafting onto that has roots is called the rootstock.
The cutting or branch that is grafted onto the rootstock is called the scion (pronounced sahy-uhn)
The basic procedure is as follows:
- The scion is prepared by making two sloping cuts at its base to form a wedge 2.5 to 3 cm long (depending on how thick it is).
- The rootstock is pruned at the desired height (if grafting to top) or its branch is pruned part way (if grafting to branch) and a clean edged cut is made down the centre of the stem for about 3 cm.
- The scion wedge is inserted into the rootstock, with one or both edges lining up perfectly to match the cambium layers* (If the scion wedge has a thicker side, match the edge on this side).
- The union is tied firmly with grafting tape to seal the union, and to prevent moisture loss, and to stop scion movement.
* The cambium is the thin green layer of tissue located just beneath the bark, between the bark and the wood, and is a layer of actively growing cells which produce the wood, bark and vascular tissue of the plant. In making a graft the object is to place the cambium of the scion in close and firm contact with the cambium of the rootstock by accurately lining up the outer surface, then binding it carefully so it doesn’t move. The cuts to scion and rootstock must be made with a very sharp, clean blade to obtain a flat, clean surface and minimise damage to the tissues.
How To Graft the Devil Plant
Step 1. Gather Required Materials
Now, you won’t need all these things to perform a graft, as some are optional, but you will need most of them.
On the left hand side, from the top down:
- Grafting Tool or Small Craft Knife or Grafting Knife (use any one of these)
On the right hand side, from the top down:
- Plastic bag and wire tie
- Clothes Peg
- Strip cut from thick plastic bag, about 50cm long and 1.5cm wide, or grafting tape (use any one of these)
- Piece of shade cloth
Step 2. Prepare the Scion
Select your eggplant for grafting, and using secateurs cut a tip or branch about 5-10cm long to use as a scion.
Here is a pruned tip of an eggplant ready to prepared as a scion
Cut away all the large leaves from the scion, leaving only small leaves and buds.
This prevents moisture loss and increases the chances of the graft surviving.
Now you’ll need the grafting tools for cutting the wedge shaped end of the scion.
Pictured below is a grafting knife and an automatic grafting tool.
Any sharp, clean knife will do the job, and a small cheap craft knife (the “Stanley knife” style with snap off blades) shown on the right works very well.
The scion is prepared by making two sloping cuts at its base towards the end to form a wedge 2.5 to 3 cm long.
Completed scion with “V” or wedge shaped end.
In case you’re wondering why use a dedicated grafting tool, well, I’ll tell you. It makes precise, exact matched cuts that fit together perfectly, that’s why!
And furthermore, if the grafting tool has a “keyhole” or “omega” blade, then the scion and rootstock can be cut to “key” together like a jigsaw puzzle piece, as shown on the scion below.
This luxury will set you back close to the hundred dollar mark though, and it is a luxury, not a necessity…
Step 3. Preparing the Rootstock
Using secateurs, cut the branch you wish to graft to at the desired length, remove the spines where you intend to graft (to prevent injury to your fingers!) if you like, and remove any leaves from the branch.
Using a grafting knife, make a split or “cleft” through the center of the stock and down 2.5 to 3 cm to match the wedge on the scion.
Step 4. Insert the Scion
Insert the scion into the split or cleft in the end of the rootstock branch. The cambium of the scion should contact the cambium of the rootstock. If the rootstock is thicker than the scion, then just line up one side.
If you find that the rootstock is too hard or woody to open up, you can cut a very thin wedge out of the end of the rootstock that is smaller than the wedge on the scion, then use the knife to pry it open while you push the scion into it.
Step 5. Bind the Graft
Secure the graft tightly with grafting tape to prevent moisture loss and to stop the graft from drying out.
Make sure that the grafting tape is wrapped tightly around the graft join, and extends over part of the rootstock and scion to make an airtight seal.
If you don’t have grafting tape, you can cut strips from a sturdy plastic bag, which is what I have used here. I get the same success rathe as I do with proper grafting tape. The strips need to be about 50 cm long, and I cut them about 1.5 cm wide. Remember that a bag is doubled, so when you cut across a 25 wide bag, you get a “loop” which is 50cm long when you make a cut in it.
The success rate of grafting will be greatly enhanced if the newly completed graft is covered with a small plastic bag and tied on the bottom with a wire tie to allow both a build up of heat and humidity.
I add a few drops of water in the bottom to increase humidity, and get a bit of air inside the bag before tying it off, so the bag isn’t hanging off the scion. I’ve also found that tying one corner of the bag to a higher branch lifts it up so it is not draped over the graft.
If the plant is in a shaded greenhouse, then it will be fine, but if it is exposed to the sun, then the graft will need some shading otherwise the scion will get steamed and cooked in the plastic bag.
Some prefer to place a small brown paper bag over the plastic bag to prevent excessive heat build up, but my preference is to use a small piece of shadecloth to let some light in.
Just simply fold a piece of shadecloth around the bag, and fasten it with a clothes peg. If you have multiple grafts, you can place one larger piece of shadecloth over all of them at once.
Step 6. Removal of Bags and Grafting Tape
With a eggplant graft to a Devil plant, I have found that I can remove the plastic bag after one week.
The grafting tape can be left on until the grafts show some decent growth, which can be over a period of a few weeks. If left on too long (months) the tape may restrict growth by becoming too tight n the graft area.
In a few weeks the grafts will flower and fruit, prolifically!
A Few Afterthoughts…
All the grafting pictured was carried out mid-summer, because that’s when my eggplant seedlings were large enough to take cuttings from. I have carried out about a dozen eggplant grafts on the one Devil plant, and they have all taken successfully. Tomato can also be grafted on to the Devil plant, and you can have both eggplants and tomatoes grafted onto the same tree too. There’s nothing like experimenting to see what works. I’ve even added two cherry tomato grafts, and they worked out too. I’ll need to figure out how to cover the plant for winter, and what to use to protect the grafts from the cold.
This grafting process make plants that are annual in cold climates into perennials. I have seen tomatoes grafted onto Devil plants in greenhouses fruiting almost all year round, and I have seen outdoor eggplant grafted Devil plants survive a winter and fruit for their second year here in Melbourne, Victoria. So yes, it really works! This will definitely change the way you grow tomatoes and eggplants…