Seeing new roots forming on a cutting you have done is always a magical feeling, particularly if it is a plant that is difficult to propagate. Many species can be propagated in your backyard or balcony with a minimal level of facilities. By understanding a little bit about the science of root formation you can dramatically increase the range of plants that can be successfully rooted.
The main types of stem cuttings are soft tip, semi-hardwood and hardwood.
Soft tip cuttings can be taken any time the shoot tip is actively growing. Soft tip cuttings are succulent and wilt very easily and therefore require a bit more environmental control than cuttings from harder wood. However, soft tip cuttings strike more easily and are faster than those of harder wood. Herbaceous plants like everlastings and other native daisies and fan flowers are all propagated by soft tip cuttings and can even be struck in a glass of water kept in filtered light on a window sill.
Semi-hardwood cuttings are generally available from late spring through into autumn as the new spring growth starts to become woody on trees and shrubs. The advantage with this type of cutting is minimal need for environmental control since there is no soft growth at the tip of the cutting. A sheltered position in the garden is all that is required. Semi-hardwood cuttings are identified by the fact that the stem is changing in colour, generally from green to reddish or brown and has fully formed leaves right to the tip. Bottlebrush, banksias and grevilleas are classic examples of plants that are ideal for semihardwood cuttings.
Hardwood cuttings are available from autumn through winter but for some species the harder wood further back on the stem can be used at other times of the year.
Hardwood cuttings have stems where the colour has changed completely to brown. These are the toughest of all cuttings and do not need any special treatment. They are identified by having a distinctly dormant terminal bud and the wood does not snap cleanly when bent. Waratahs are a good example of a native plant that can be propagated by hardwood cuttings.
Special tips on how to improve success:
Wounding the base of cuttings- New roots form on cuttings in the tissue just below the outer ‘skin’ of the shoot. This is the tissue that conducts the water and sugars and is called the vascular cambium. When cuttings are taken of harder wood we can stimulate faster and better root formation by scraping off the surface tissue on the base of the cutting to expose the sappy conducting tissue where the new roots form.
Hormone treatments to increase rooting rates – So called rooting hormones are a group of substances known as auxins which regulate all sorts of activity in plant growth. Importantly for us they stimulate new root formation. Auxins are generally applied to the base of the cutting and are particularly effective where the tissue has been wounded. Auxins are often applied as powders but auxin gels and liquids are also available that have other substances such as vitamins added that are known to further stimulate the rooting process.
What media to use for maximum success – A well-aerated potting mix is very desirable for cuttings as the extra pore space allows for good oxygen exchange which fuels the respiration of the rapidly dividing new root cells. Special cutting propagation mixes are available or you can manufacture your own by adding 50% coarse sand or perlite to a standard potting mix.
To learn more about propagating, read about sowing seed-
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