Propagating plants by cuttings 101
Should I use softwood, semi-hardwood or hardwood cuttings and when?
Propagating plants at home with cuttings is relatively easy and in this time of climate change we need all the plants we can get. It is also quite satisfying being able to say I propagated it myself. The time of year of taking cuttings and the species are both important factors. Some species don’t strike readily from cuttings and seed is needed.
Cuttings are pieces of plants made to form roots, and when they do grow roots, they are said to strike. The cutting when placed in propagating sand should form a callus on the cut end and then grow roots from the callus. Striking roots may take a few weeks to a few months.
This article will cover the soil or propagating sand to use; the moisture and temperature; tools; cutting material; the types of cuttings and timing; and some species of plants suitable for cutting propagation.
A propagating sand for use in containers needs to be a clean, coarse grained, sharp sand. Sharp meaning each grain of sand is angular in shape, not round, reducing the tendency to pack together. Good drainage resulting from large pore spaces is required, this allows for more aerated soils which are less suitable for fungal growth.
Sometimes the term double washed sand is used, this is suitable for cuttings, as most of the clay and organic matter has been leached out with water. Other sands, such as bricklayer’s sand and orange plaster’s sand are not suitable for cuttings because of the clay content, which holds more water and reduces the aeration.
Propagating sand is better if it has a neutral pH or slightly acidic pH of 6 Soil pH.. A measure of the acidity or alkalinity… | by Peter Miles | Medium
Sand is often alkaline and mixing sand with peatmoss or compost which are slightly acidic will make the mix neutral. Suitable mixes are 50:50, or 25% compost to 75% sand.
Compost is a good environmentally sustainable alternative to peatmoss, which comes from peat bogs which are carbon sinks.
The addition of peatmoss or compost will increase the water holding ability of the mix, and also reduce the tendency of sand to run out the drainage holes of the pot or tray.
Often potting mix is suitable for the easier to strike cuttings, it has been used in the photographs here. Although any fertilizer it contains is not needed for cuttings and the potting mix may hold a little too much water.
Some cuttings can also be propagated in garden soil in the ground but again light sandy soils will allow for better drainage; having said that heavier clay soils are often quite suitable for hardwood cuttings, see below types of cuttings section.
Water alone can be used to strike species which root easily, such as Coleus, oleander and willow, but the stuck cutting still has to cope with the transplant shock of being planted into potting mix or soil.
The important point here is that a cutting mix needs to be well aerated. Cutting should only be inserted deep enough to provide support, the top part of any media in a pot or garden soil will be the most well drained, providing better aerated conditions for striking cuttings.
The moisture and temperature are important factors to consider for successful striking of cuttings. Cuttings require humid conditions to reduce transpiration from the leaves as they have no roots to take up soil water, although they can absorb some water through the cut end of the stem, much as cut flowers in a vase.
Higher humidity can be achieved by covering the cuttings with clear plastic as seen in the photograph below, the plastic retains some of the moisture transpired from the cuttings and evaporated from the propagating mix. The required humidity is achieved in plant nurseries by propagating cuttings inside glasshouses. In the home garden a simple wire framework supporting a clear plastic bag over a pot of cuttings is often sufficient, allow for a little ventilation and ensure the cuttings are in a sheltered position and shaded so as not to get too hot under the plastic.
Temperature is most easily regulated by taking cuttings in the milder season of autumn. Spring is suitable for easier to strike species, but often plants are flowering in spring and putting their energy into flowering rather than growing roots. Winter is used for deciduous species by hardwood cuttings in the ground.
Commercial propagating units are available, which provide misting onto the cuttings controlled by a timer, this doesn’t replace watering, cuttings still need to be watered and probably most days. Propagating units may also have bottom heat, through electric low voltage heating cables underneath the cutting containers, providing heat from the bottom to stimulate root growth rather than above heat encouraging leaf growth. A propagating mix temperature of approximately 22 degrees C. is required.
Bottom heat and mist propagation units encourage cuttings to root in a shorter time, which may be an advantage to nurseries but generally not essential in the home garden. Still, striking with propagation units can be quite rewarding.
Sharp tools are required when preparing cuttings, this is to prevent bruising of the stem tissue of the cutting, which then may be an entry point for fungal disease. Propagation purists may only like to use a knife, in order to prevent bruising, but this requires a lot of practice to prepare cuttings without also cutting your thumb.
Sharp bypass secateurs are safer and quite sufficient, most secateurs are bypass, where the blade slices passed the block, that is it bypasses. The block can bruise the stem of the cutting, so if possible, have the block press against the part of the stem that you are discarding, not the cutting.
Cleaning of your secateurs or knife, again to prevent fungal diseases, can be done with methylated spirits or a weak solution of sodium hypochlorite, which is in some laundry bleaches.
Cuttings will strike better if taken from plants that are in good health and have possibly been watered and fertilized. Nurseries will often keep well maintained stock plants specifically for providing cutting material.
Plant material with a high carbohydrate to nitrogen ratio will strike easier. Vigorously growing plants shoots have a low carbohydrate to high nitrogen ratio and should be avoided for cuttings.
Shoots with thin, round stems are generally better material for cuttings.
Young plants which haven’t produced flowers yet can make better cutting material, or mature plants that have been pruned to encourage juvenile growth. Growth from the base of plants often strikes better than growth at the top.
A rule of thumb is not to propagate from plants in flower, as the plant is placing its food reserves into flowering not so much into roots, and if you can’t avoid flowering, pinch off the flowers. Some species of Correa for example, seem to be in flower through autumn, winter and spring but in this case the flowering doesn’t appear to affect striking.
Preparing cuttings. Cuttings can be made from growing tips and from further down the stem, the base cut should be straight across the stem close underneath a node, also called a bud. Too much excess stem material left below the node is prone to fungal infection.
The top of the cutting, if not a growing tip, can be cut at an angle, possibly providing for shedding of water from the top end of the cutting, but also useful to tell which end is up! Upside down cuttings don’t do very well, unless they are very vigorous plants like ivy or bamboo.
It is ok to leave part of the internode section on the top of the cutting, above the top node, this also gives something to hold when handling the cutting.
The size of the cuttings is determined by the size of the plant material and leaves, between 50mm and 100mm long for most plants but hardwood cuttings can be 200mm long.
Remove the lower leaves to allow insertion in the propagating mix and to reduce the number of leaves transpiring. Some leaves are required to continue photosynthesis.
With small leaf plants, such as Coleonema pulchrum pink diosma, the bottom two thirds can be stripped off. This may usually be done between the thumb and finger with a downward motion.
Larger leaf cuttings have the lower two thirds of the leaves cut off and possibly the remaining leaves are cut in half. If the humidity can be maintained, to reduce transpiration, cuttings left with a few full leaves often perform better.
Cuttings should only be inserted into the propagation mix only far enough to hold them up, as said before, the upper part of the propagation mix has more aeration, encouraging roots to strike.
A hole should be made in the propagation mix first with a stick or dibbler, this enables inserting the new cutting without any abrasion of the stem from the sand, this abrasion is wounding and may result in fungal infection. Cuttings can be placed in the propagating mix about 10mm apart, or more depending on the leaf size, but in any case, ensure there is enough room between cuttings to allow air movement.
Commercially available rooting hormone powders can be applied to the bottom ends of cuttings before placing into the propagation sand but are not essential. These generally contain indole butyric acid, a growth hormone.
You can make your own rooting solution with honey or Aloe vera which are both antibacterial reducing attack on the cuttings; or aspirin that contains salicylic acid which is antifungal and a plant hormone; or willow bark which contains both salicylic acid and indole butyric acid.
Types of cuttings. Most cuttings are pieces of stems, which will be covered here, but leaf cuttings and root cuttings are also used. There are three types of stem cuttings, softwood, semi-hardwood or hardwood cuttings.
Softwood cuttings are made from stems of fresh new growth, the wood is soft and flexible hence the name, and cuttings can be made from herbaceous shrubs, such as Coleus and Plectranthus, and from new growth on woody shrubs. Often this type of cutting is taken in late spring into summer after the spring flush of growth. Chrysanthemums and carnations are propagated from softwood cuttings.
Semi-hardwood cuttings are made from wood that has mostly stopped growing and is becoming woody. Semi-hardwood cuttings are often taken in autumn, by the time autumn comes woody material is forming, but generally spring, summer and autumn are suitable.
In hot, dry climates avoid taking cuttings in the middle of summer when it is hottest, and in cold climates ensure any struck cuttings and new young plants are given ongoing protection from the very cold winters.
Semi-hardwood cuttings are used for the majority of species, such as Camellia, Coleonema and Aucuba. I’ll provide a more extensive list at the end of the article.
Hardwood cuttings are made from mature wood that won’t grow any more until spring and are taken in autumn or winter. If the winters are very cold and the cuttings are planted outside and could be subject to injury, the cuttings are made in autumn.
Hardwood cuttings are used for deciduous species and conifers, and generally take longer to strike but are not affected as much by the surrounding environment. Also used for grapevines.
They are usually planted into the ground, allowing sufficient room between for root and shoot development, or they can be inserted into a container of sand.
Different methods of preparing cuttings have been used, usually with semi-hardwood cuttings and mostly the straight stem cutting method. The heel cutting, see image, which includes a heel of vascular tissue from the adjoining branch, is often more successful in growing roots and it is a useful method for hard to strike species.
Determining if the cuttings are rooted is usually a matter of patience as it is difficult to tell without upending the container. Lift up the container of cuttings and look for roots coming out the drainage hole in the base or sides, this is the best indicator but keep in mind that it will take several weeks, even months.
It is best not to allow too much root growth before potting on, as damage can occur when trying to separate the individual cutting roots because of intertwined roots.
Here are just some Genus that are propagated by cuttings:
Easier cuttings which generally strike within 8 weeks. Most of these are propagated by semi-hardwood cuttings unless specified.
Buddleia also by hardwood cuttings, Buxus, Correa, Euonymus, Euryops, Helichrysum, Lavandula, Lonicera, Murraya, Myrtus, Prostanthera, Rosmarinus, Salvia, Syzygium.
Pelargonium sometimes called Geranium are quite easy to strike, just break off a piece and put into the ground where you want the new plant.
More difficult cuttings, which may take 3 to 4 months to strike. Again, most of these are propagated by semi-hardwood cuttings.
Adenanthos, Azalea, Boronia, Bougainvillea, Camellia, Daphne, Gardenia, Grevillea, Juniperus, Leucadendron, Protea, Rhododendron, Teucrium.
To recap, three types of cutting, softwood, semi-hardwood and hardwood cuttings and they can be prepared in spring, autumn and winter respectively, although there is overlap of the seasons. Semi-hardwood cuttings can be used for most cutting grown plants. A well aerated and drained propagating mix and adequate humidity are most important.
Declaration of competing interest. I have no conflicts of interest to disclose.
Reference:
Chittenden, F.J., (1977). The Royal Horticultural Society. The Dictionary of Gardening (2nd Ed.) Oxford. Great Britain. University Press. Book.
