Raising new plants from cuttings is one of the most reliable ways of propagating. In general, the technique involves taking a small piece of material from a living plant. After inserting into a rooting medium, the cutting is able to produce new roots and is then carefully nurtured until large enough to be potted on.
The main advantage of taking cuttings is that cuttings up to 1" thick (dependant on species) can be rooted, speeding up the process of creating a plant suitable for use as bonsai. The other advantage with cuttings is that material that is routinely pruned from bonsai and thrown away, can be used to create new plants.
There are a wide range of cuttings in general horticultural use that can be used to propagate garden plants, from leaf-cuttings to root-cuttings; for bonsai however it is stem cuttings that are normally used. There are 3 types of stem cuttings commonly used, softwood cuttings, semi-ripe and hardwood cuttings.
The Species Guides at www.Bonsai4me.com list the best method and the correct timing for taking cuttings from each species. This gives you an idea of how to achieve good success rates when taking cuttings, however, if material becomes available at the 'wrong time', it can still be worth trying to use it rather than throwing it away. There may be an increased failure rate but you may also gain a number of new plants.
Softwood are the soft, pliable shoots from the current seasons' growth. More often than not, they will be green-wooded. These are nearly always taken in Spring to early Summer when the new leaves on the shoot have hardened off and changed from their Spring colour.
Try to take these cuttings early in the morning if possible. Each cutting should be 8-10cm (3-4") if at all possible, trim the cutting from the host plant just below a leaf node. This is where there are likely to be adventitious buds that will hopefully root in the future. Cuttings that can be taken just below the junction of a side shoot are nearly always more successful as they have a high concentration of natural growth hormones. Trim all leaves off the lower third of the cutting and reduce leaves on the upper two-thirds to just 3-5 pairs at most.
SEMI-RIPE AND RIPE-WOOD CUTTINGS
Semi-ripe cuttings are generally taken in mid- or late Summer; they consist of soft-tipped shoots of current seasons' growth (as with softwood cuttings) but have firm and woody growth at the base.
Ripe-wood cuttings consist of the same material as semi-ripe cuttings but have ripened up further and are generally taken from early Autumn to early Winter.
The cutting is taken just below a node for nodal cuttings or with a heel of mature wood for heel cuttings.
Remove all side shoots and trim nodal cuttings to 8-10cm (3-4") long if possible, trim heel cuttings to 5-7cm (2-3") long if possible. Remove leaves on lower third of cuttings and for semi-ripe cuttings also remove soft tips. Reduce large leaves by half.
Hardwood cuttings are taken in Autumn (after leaf-fall) to early Winter. They consist of the leafless shoots of fully ripe growth up to 1" in diameter. Trim to 15-23cm (6-9") if possible, with the top cut just above a bud or pair of buds and the bottom cut just below a bud or pair of buds.
Cuttings should be dipped into rooting hormone and inserted into a seed tray or plant pot of a standard pre-mixed cutting compost or equal parts peat (or substitute) and perlite or sharp sand.
Ensure that the compost is kept damp at all times but do not allow to become too wet. Cuttings' leaves should not be allowed to touch. Watering with a fungicide solution will lessen the chances of fungi infestation.
Softwood cuttings need to be placed in a propagator to ensure humidity levels are kept high and moisture loss is kept to a minimum. Alternatives include placing the cuttings container in a plastic bag or frequent misting. Softwood cuttings need to be kept at 18-24°C if at all possible. At this time of year, this usually means placing on a bright window-sill out of direct sunlight. Fallen leaves should be removed daily to avoid fungal growth which can kill cuttings. As the cuttings start to grow strongly, propagator covers or plastic bags should be removed. Softwood cuttings can start to show signs of growth within 2 or 3 weeks, they do not however root for far longer and should not be disturbed or repotted until roots start to appear at the bottom of the container. It can take as long as a year before softwood cuttings are strong enough to be potted on individually.
Semi-ripe and ripewood cuttings should also be placed in a covered propagator to ensure high humidity levels, though at this time of year (Summer or early Autumn) the container is normally placed outside where temperatures of around 21°C are ideal. Do not place in direct, hot sun which can dry out the cuttings before they are able to root. As with softwood cuttings, remove fallen leaves on a daily basis and keep the compost damp but not soaking wet. Semi-ripe and ripe-wood cuttings are normally strong enough to be potted on the following Spring.
Hardwood cuttings should be placed outside and do not require any cover; there are no leaves to lose moisture and humidity levels during the Autumn and Winter are naturally high. Hardwood cuttings require no more protection from frost than their parent plants and only need extra protection when temperatures drop below -10°C. Ensure that after frosts, cuttings are re-firmed into the compost as frozen compost can lift and create air-pockets.
Hardwood cuttings will show no outward signs of growth until Spring when tiny buds will start to appear. They can be as late to start growing as May and until then should be left undisturbed. Hardwood cuttings do not generally begin to root until after their first flush of growth and unless growth is particularly vigorous should not be repotted until the following Spring; around 15months after being originally taken.
TIPS FOR SUCCESS
If a diagonal cut is made to the bottom of cuttings, it helps to indicate which way up the cutting should be planted. The increased surface area of a diagonal cut also gives an increased area for roots to appear.
Keep humidity levels high for cuttings with leaves as this reduces moisture loss; however be wary of fungal infestations that enjoy hot, humid conditions and can kill cuttings.
Remove all dead leaves daily.
Cuttings that have dropped all foliage and have shrivelled are unlikely to strike; these become a likely source of fungal infection and should be removed.
Always use Hormone Rooting Powder; it contains fungicides and greatly increases rooting rates.
Take as many cuttings as you can fit in a pot but do not allow leaves to touch each other.
NEVER be tempted to pull out cuttings to inspect their root growth before they are ready; it is more likely that you will break very delicate roots which will result in the cuttings failure
Be Patient !!