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Propagation

by Rudi Adam

A common and useful method of propagation for bonsai growers is by means of cuttings. Propagation through cuttings has several advantages: it is cost effective because a large number can be obtained from a single tree and cuttings are true to species, and especially true to its parent stock. This makes the choice of parent stock very, very important! Although it is possible to take cuttings throughout the growing season, for some species the success rate and the quality of the new plant is greatly increased if the cuttings are taken at certain times.

Ulmus parvifolia - The Chinese elm (Including all its varieties)

The elm may be the most commonly used species for making cuttings in bonsai. To achieve a particular style or growth habit it is important to know which parts of the parent plant to use for cuttings.

TOP CUTTINGS

Forest plantings and Upright trees.

Select strong, straight top growth, between 6 - 16cm long, at least one growing season old. Separate it from the parent with a heel ( i.e. with part of the stem or branch from which it emerges) if possible. The benefits are that more cambium is exposed for a greater amount of roots and it gives the new plant a better flare at the base from the start. If you are planning a mame or shohin bonsai, start with a shorter cutting. If heeled cuttings are not possible, then cut the slip into 4 or 6 unequal lengths. Split the bottom of each piece and insert a small pebble to flare the base before inserting it into the rooting medium. Such cutting may be taken at leisure during the midwinter months, immerse them in clean water or in a solution of water and SUPERthrive or Rescue Remedy for about 15 minutes. Shake off all the excess moisture, bundle the cuttings up and place in a plastic bag. This can be stored in the vegetable tray in your refrigerator for up to 8 weeks and it also promotes the formation of callus tissue. In spring, with its warmer weather and longer daylight hours, prepare a deep seed-tray by filling with a commercial seed mixture up about 5cm. Cover the entire surface of the seed-tray with glass marbles/spheres 2-3cm in diameter. Insert the cuttings into the growing medium up to 4cm deep through the apertures between the balls, remembering to space them well. The balls will hold the cuttings in an upright position. (It may be necessary to add a second layer of balls to add greater stability.) Water well with a solution of SUPERthrive or Rescue Remedy, check that the drainage is good because more cuttings are lost to rot than to any other cause, and place the tray in a protected position. After 4-8 weeks start fertilising every two weeks.

In the following spring the cuttings can be planted into individual bags/pots with a coarse soil mixture. When potting up make sure that the roots are properly flared and at least 3cm below the soil surface. After 2-3 years cut back and start with branch training, fertilise well, but leave the young trees in large bags.

When the basic structure of primary and secondary branches has been achieved start with the assembly of your forest and add the finishing branch structure. Do not forget to trim to varying heights and make sure that you have a good mixture of trunk thicknesses. This takes from 5 - 7 years.

Informal styles

The method outlined above applies, only use cuttings with interesting shapes or which have been pruned into shape. If none are available then use straight cuttings and plant them at a 45° angle to the soil surface.

ROOT CUTTINGS

The elm lends itself to root cuttings and these can be up to 2 cm thick for informal styles. Thin roots are cut straight across and thick roots diagonally. The length of stem above the root will determine the length of the future trunk, except where the cutting is very close to the division. The best root cuttings are obtained from 2-3 year old trees which have grown in a coarse mix of 2 parts stone (6mm) and 1 part compost.

Rarely are all the rootlets of the same size and they must be trimmed. Long strong ones are pruned back and weak rootlets are left intact so that they catch up in size. Normally these cuttings are taken when you repot your trees in spring. However, the later in the season they are taken the greater will be your success rate. For example, cuttings taken from November to the beginning of February will yield up to a 100% success rate. Taking root-cuttings too early means that the roots are not yet active or if taken too late means that they are not active for long enough to sustain a rate of growth and have the strength to sustain itself through dormancy. New growth emerges at the ring of exposed cambium. Remove all new shoots except two, one as the new leader and the other as the first branch.

Root-cuttings have interesting curves and loops which were produced by the roots picking their way through the gravel. You may also wire the roots very loosely now to get the effect you need. Allow the cuttings to grow unhindered until the plant is growing strongly. Now it may be cut back severely to reestablish the irregular growth pattern already established in the rest of the root/trunk.

Root-over-rock styles

Root-cuttings of up to 3cm. in diameter may be used. Try to keep the trunk height to a maximum of 5cm., especially if you are using a tall rock. Select a cutting with at least three side roots with the division fairly high up and sufficiently long to reach the bottom of the rock you intend to use. Secure the rock with twine, cloth, plastic tubing or any other suitable material which will rot away or is elastic enough to stretch as the roots thicken. Put down at. least 5 ern. of your potting mix, place the rock on it and bury the whole rock in a planting bag. This is done by filling the bag up to one-third the height of the rock with your potting mix. The last third is topped up with crushed stone of at least 6 mm in size. Leave only a small section of the cut root with its cambium exposed. Large areas of exposed cambium may produce material for a broom style. Keep the foliage close to the newly established root-base.

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Random Bonsai Tip

Mixing growing medium - To mix your growing medium, put the mixture into an empty compost bag (as much as you can handle) and tip the bag backwards and forwards - this is much easier and more effective than mixing in a wheelbarrow!