One thing a growing garden needs is plants, and lots of them! To buy enough plants to fill a regular backyard garden can be quite an expensive affair, but, thankfully, it doesn’t have to be that way. Nature provides freely and abundantly, and when we work with nature, it becomes quite effortless, and inexpensive too!
Plants naturally reproduce themselves, and they are more than capable of doing this without any help. We can take advantage of some of the mechanisms by which plants can reproduce themselves to produce an abundance of plants for our gardens.
Many herbaceous plants (plants that do not have a persistent woody stem) and even many woody stemmed plants can be reproduced if a cutting, a short length of the stem or a branch that is cut off, is put into moist ground in a partly shady cool spot. In time this cutting will sprout roots and become a new plant that is an exact genetic clone of the plant the cutting was taken from.
Softwood vs. Hardwood Cuttings
At this point you may be wondering, what the difference is between taking hardwood and softwood cuttings?
- Softwood cuttings are taken during the growing season, where the plants have leaves, so an important consideration is to maintain the humidity levels until roots begin to form to prevent the cuttings drying out.
- Hardwood cuttings are taken in winter, during dormancy, when all leaves have fallen.
When discussing propagating plants by cuttings, the question inevitably comes up – why not grow from seed?
The Difference Between Cuttings and Seed Grown Plants
The difference between growing plants from seed and growing plants from cuttings is genetic variation.
As just mentioned, cuttings are identical genetic clones of the parent plant because this is vegetative or asexual reproduction, as genes only come from one parent.
Seeds can produce plants that are different from the parent plants because seeds are produced by sexual reproduction, they receive genes from a male and female to form. As they are a cross from two sets of genes, many fruit trees are not true to seed, that is, their seeds will produce a different variety of tree from the parent. For the botany purists out there, yes, there are some exceptions, but this is generally the case.
For example, the seeds from a particular variety apple will not grow to be the same variety as the apple tree they came from. The seeds will produce a wide variety of different apple tree types.
So what you may say? Well, consider that not all the varieties of apple would taste good, some may not be palatable or edible at all!
Why do plants do this, mix and match their genetic material and constantly change? Simply, to adapt to different conditions and enhance their chances of survival and reproduction.
Now it should be clear why all commercial fruit tree varieties are grafted, the scion wood that is grafted onto a rootstock all comes from the same original parent plant, or plants grown from it.
The other great thing about propagating using cuttings is that the plant produced has the same genetic maturity as the parent plant. If a plant takes three years to produce fruit when it’s grown from seed, a plant grown from a cutting will be mature if the parent plant is, so a new plant produced from a cutting of a three-year-old plant will potentially fruit in the same year, which saves a lot of waiting around for trees to become productive.
Genetic variation isn’t as big an issue with most herbaceous plants, but we can maintain the variety if it has favourable characteristics, and it’s a great way to produce hardy, mature plants in a hurry.
Now that we’ve covered the basic theory, let’s get down to the practical matters of how to propagate plants from softwood cuttings.
Procedures for Rooting Softwood Stem Cuttings
When propagating softwood cuttings, which have leaves, there are a few extra steps required compared to using leafless dormant hardwood cuttings. Plants transpire (lose moisture) through their leaves, which makes softwood cuttings more susceptible to drying out.
Step 1 – Select Suitable Cutting
- Most herbaceous (softwood) stem cuttings are best taken during the growing season of a plant, from spring to summer, and the best time is early morning, when the plant tissues contain the most water.
- Cuttings are usually about 10-15cm (4-6”) long, from current or past season’s growth.
- Cut below a leaf joint.
If possible, choose strong, healthy, disease-free shoot for a cutting, preferably from the upper part of the plant.
- Avoid taking cuttings from plants that show symptoms of mineral deficiencies.
- Avoid taking cuttings from plants that have been heavily fertilized, especially with nitrogen, as they may not root well.
- Avoid taking cuttings from plants that show moisture stress.
It is important to keep the cuttings cool and moist until they are placed into the propagating medium. When working with cuttings, don’t lay them out exposed to full sunlight, work in a shady spot!
If the cuttings need to be transported, wrap them in a moist paper towel in a plastic bag. If there is a significant delay in potting up the cuttings, they can be stored in a plastic bag in the refrigerator.
Step 2 – Strip Off Lower Leaves
- Remove the leaves from the lower one-third to one-half (1/3 – 1/2) of the cutting to leave a bare stem. This allows the lower portion of cutting to be inserted into the propagating medium, and also reduces the number of leaves from which moisture can be lost.
- Remove any flowers and flower buds when preparing cuttings so the cutting’s energy can be used in producing new roots rather than flowers.
On some plants with small leaves, it’s possible to strip off the leaves easily by holding the top of the cutting firmly with one hand, then using the other hand to pinch the lower part of the cutting and pull gently downwards. If this doesn’t work, trim the leaves away with scissors or secateurs.
If too much moisture is lost, the cutting will dry out. Remember, the cutting doesn’t have any roots yet to pull up more water to replace that which it loses! On large-leafed plants, to reduce the rate of water loss, cut all the leaves in half by trimming the ends off. This also reduces the size of the cuttings, so they take up less space. When new growth with uncut leaves emerges, this is an indicator that the cutting has produced roots and is growing!
Step 3 – Cut Stem Below a Leaf Node
- Cut the stem about 6mm (1/4”) below the lowest leaf node on the cutting.
The leaf nodes are the areas where the leaves grow out from the stem, which are now stubs from where the leaves were removed earlier. If the area of the stem has no leaves, it may still have visible buds from where new leaves will grow.
The reason why we cut near the leaf nodes is because these areas contain a large area of meristem tissue. Meristem cells are undifferentiated cells, similar to human stem cells, that can grow and divide to form various kinds of cells for plant growth, including new roots.
The cells in the meristem divide quickly and form callus to seal the end of the cutting, and then under the influence of the plant’s own hormones, auxin and cytokinin, these callus cells differentiate to become root cells.
Hardwood species that are difficult to root are often ‘wounded’ by scraping away the bark using a knife to expose the light green cambium layer underneath, which helps promote rooting. Herbaceous plants don’t have woody tissue, and don’t have a cambium layer either, and therefore do not require this step.
Step 4 – Dip End of Cutting into Rooting Hormone (optional)
- Dip freshly cut end of softwood cutting into root hormone liquid, powder or gel. Treating cuttings with rooting hormone can increase the chances of stimulating root growth. This is more critical in plants that are more difficult to root.
- If using root hormone powder, be sure to tap the cuttings to remove excess.
Most commercially available rooting hormone products consist of two synthetic auxins (plant hormones), indole-3-butyric acid (IBA) and naphthaleneacetic acid (NAA), discovered in 1935. They have similar functions to the auxin naturally produced by plants, indole-3-acetic acid (IAA) which was first identified in 1934 and are more effective in promoting root formation. Afterwards IBA was also found to be naturally occurring in plants. Commercial rooting hormones usually also contain a fungicide to prevent fungi from causing rotting of the cutting.
It’s possible to make your own natural rooting hormone, see article – How to Make Home Made Plant Rooting Hormone – Willow Water.
Willow water is mild form of root stimulating hormone which contains IBA that can be made quickly and easily from willow tree twigs.
Step 5 – Insert Cuttings into Pot Filled with Propagating Medium
- Fill a pot with propagating medium. Materials commonly used as propagating medium are coarse sand, regular potting mix, coconut coir, or blends such as a mixture of one part peat and one part Perlite (by volume), or one part peat and one part sand (by volume).
- Water the propagating medium to moisten it.
- Insert one-third to one-half of the length of the cutting into the propagating medium. Keep the cuttings vertical and space cuttings far enough apart from each other so they don’t shade each other out so that all their leaves can receive light.
Any medium which will lend physical support, provide moisture and oxygen in the right balance, is low in fertility and is free of pathogens can be used for propagating cuttings. The reason the propagating medium doesn’t need to contain nutrients is because the cuttings don’t have roots to be able to take them up.
The propagating medium also needs to be well-draining to provide sufficient aeration to grow roots. If it is anaerobic (no air), the roots will rot, as very few plants can grow roots in a container of water. Conversely, the medium should also retain enough moisture so that watering is not required too often.
Step 6 – Add Additional Cuttings to Increase Success Rate
Since cuttings don’t always ‘strike’ (grow roots), and some plants are notoriously difficult to propagate, it’s best to add a few extra cuttings into the propagating medium to increase the chances of success.
Even with plants that have really low striking rates, say as low as 20%, if we put in 10 cuttings in, we’ll potentially get 2 cuttings that take root.
Step 7 – Label the Cuttings to Identify Them
I can’t emphasise enough the importance of labelling plants when propagating by seeds or cuttings.
We might remember what plants and varieties we planted on the day, but what are the chances that we’ll remember after many weeks or months that they make take to grow roots? What are the chances of telling them apart?
Step 8 – Cover the Cuttings to Retain Moisture
- Cover cuttings in some way to prevent them drying out while still allowing them to be exposed to light.
- Set the cuttings aside in a bright, warm location, away from direct sunlight.
In order for cuttings to survive, they need to retain moisture within them. The leaves are able to lose moisture via evaporation, but the cuttings unfortunately don’t have any roots to take up more water to replace what is lost from the leaves.
The way to keep the cuttings alive is to maintain the humidity levels (moisture in the air) around them, while at the same time avoiding excessively damp conditions that will cause them to get mouldy and rot!
To do this, we lightly water the cuttings, and then cover thems with some kind of clear plastic that will hold in the moisture, and then place them in indirect light.
- Avoid direct sun, otherwise the cuttings will overheat and cook in their airtight enclosures!
- Keep the propagation medium moist until the cuttings have rooted.
Smaller pots can be placed inside a plastic propagation tray, these sell for a few dollars and last quite a while, they’re available at most nurseries and garden stores. Note the green air vent ‘butterfly’ on the top of the lid. This allows the vents holes in the lid to be opened which lets out the heat if it gets too warm, or to reduce the internal humidity when the cuttings start growing and need more air flow.
Some gardening books recommend covering pots with a plastic bag and securing them around the pot with a rubber band to retain the humidilty. Since the bags collapse around the plant, keeping the leaves wet, the suggested solution is to place a wire loop shaped like an inverted-U over underneath to prop up the plastic bag.
I’ve never been satisfied with that solution, so I came up with a better one. Here’s an effective design for a humidity cover that I’ve devised!
A regular plastic drink bottle can be cut in half, and pushed slightly into the propagating mix in the pots to seal the moist air in. The top halves of the bottles are more useful as the lid can removed for greater ventilation.
Taller cuttings can be accommodated by cutting off the bottom of the plastic bottle only, creating a taller humidity cover. These work like traditional cloches and can be used to protect seedlings in the garden from snails and slugs. Just remember to take the lid off otherwise the plants inside will overheat and get cooked in direct sunlight!
Step 9 – Harden Off Cuttings When They Show New Growth
The time taken for cuttings to ‘strike’ (produce roots) varies, depending on the type of plant, and the environmental conditions – heat, light and season. Some plants root readily while others can take what seems like forever. If the cutting still looks alive, be patient!
Newly rooted cuttings should not be transplanted directly into the garden. They need some time to adapt and harden off.
Hardening Off Procedure for Cuttings
When using the clear plastic bottle cover, the following hardening off process can be used:
- Wait until new growth appear, indicating that the cutting has rooted.
- Remove the lid of the bottle to reduce the humidity level around the plant, and leave this way for one week.
- Next, remove the whole plastic bottle cover, and leave the plant uncovered for a week.
- Move the plant into a slightly sunnier location so it can adapt to brighter light and slightly drier conditions and leave it there for a week.
- Finally, move it out to a location matching its light requirements and necessary exposure/protection.
After hardening off a plant, it can be planted out the garden, or transplanted into a larger pot with proper growing medium (potting mix) to provide it with some nutrients. Avoid the urge to overfeed newly propagated plants, fertilise them lightly, as their roots are still quite delicate.
There’s no hurry to plant out newly propagated plants. Growing them on to a larger size allows them to develop stronger root systems, which makes them much more resilient, and increases their chances of survival when they’re finally transplanted to their permanent location.