Layering is one of the oldest techniques used by gardeners to propagate woody plants. A stem is encouraged to develop roots before it is removed from the parent plant. This [ method is easy as it avoids any complicated ' environmental control to ensure the stem ■ survives while the root system is developing. The early gardeners had probably observed this process when it occurred naturally under i certain conditions. To do it artificially they just repeated the conditions and modified the technique. I As with any method of propagation, it is i necessary to consider both the stem from I which the layer is to be made and what soil | is suitable to encourage rooting. '! The condition of the stem will have a significant affect on the eventual success of I propagating by layering. For greatest success, the gardener should develop vigorous, rapidly grown stems with their high capacity to produce roots. Certain methods of layering, | such as stooling, encourage this capacity in j stems as part of the normal system of management, but in others, such as simple layering, it is necessary to prepare the stems by pruning the parent plant well before j propagation can take place. When pruning ' ; bear in mind that, with most methods of I layering, the branches to be layered will have to be brought down to ground level.
The soil around the parent plant will also require preparation so that it will induce the stem to form roots. Rooting will be encouraged I- primarily by the exclusion of light, but also by | the availability of oxygen and the presence i t of sufficient moisture and warmth. • The exclusion of light from the stem, that is blanching it, is extremely important when , encouraging roots to start growing. The ! sooner light is excluded from the stem, the I more effective is the response. So, the earlier a stem is buried or earthed up the more likely it is to root. This effect cannot ■ be overemphasized, as lateness in earthing up is probably the commonest reason why ■ ;' a stem fails to produce roots, provided that í¡ it is basically vigorous and capable of pro-'' ducing roots.
; The soil for layering must have a good | water-holding capacity, good aeration and | adequate drainage. Thus, especially if plants are to be layered in an ordinary garden border as opposed to a purpose-developed layer bed, the soil must be dug deeply to provide good drainage and so reduce the chances of waterlogging. It can be further lightened and improved by the addition of peat and/or grit, depending on the heaviness of the soil.
Warmth will improve rooting, so ensure the layered stem and soil are placed where they will receive adequate sunlight. However, warmth will only be effective if the soil is moist, so water the layered stems during dry periods.
In most methods of layering, the soil should be carefully forked away from the layer once it has rooted, so it can be lifted. Do not allow the roots to dry out, otherwise they will die.
Layers that may have difficulty rooting successfully should be well established before they are lifted. To encourage this, sever the newly rooted layers from the parent plant about three to four weeks prior to lifting and replanting.
This weaning can be further enhanced by pruning the stems so that there is a greater balance of root to stem.
Simple layering is perhaps the easiest and most effective method of layering a wide variety of woody plants, and it is a technique that can be carried out with minimum disturbance to the parent plant.
A stem is buried in the soil behind its tip so that roots are induced in this area. Once the root system is established, the stem can be severed from the parent. The roots are encouraged to develop because the plant foods and hormones are restricted where the stem is buried. To be successful, the gardener must use stems that have a high capacity to produce roots, and they should also be near ground level.
Twelve or more months before layering, rigorously prune a low branch or branches on the parent plant so that young, rapidly grown shoots are produced. These will be more amenable to the bending and manipulation involved in the actual layering operation, and because of their rapid growth will have the required capacity to produce roots.
Layering is normally done in late winter/ early spring, as soon as the soil can be worked down to a tilth.
As the technique is likely to be carried out in the garden and not in a purpose-prepared nursery bed, it is important to prepare the soil both thoroughly and effectively. Dig as deeply as possible. Then add peat and grit in sufficient quantities to convert the existing soil into a rooting medium with good water-holding capacity, good aeration and adequate drainage.
Trim a rapidly grown stem of side-shoots and leaves for about 4-24 in behind the tip. Pull the stem to ground level and mark its position on the soil 9 in behind its tip. Dig a trench from that point, with one straight side about 4-6 in deep and the other sloping up to ground level near the parent plant.
The secret of inducing root formation is to restrict movement of food and hormones in the tissues of the stem: this is usually achieved by bending the stem at least at a right angle. However, in plants that are particularly difficult to root, the stem should first be girdled by cutting into the stem with a knife or by binding the stem tightly with a piece of copper wire at the bend.
Bend the stem at right angles 9 in behind its tip and set it in the trench against the straight side with its tip exposed above the trench. If the stem is whippy, peg it down with heavy wire staples. Bury the stem with soil, firm in and water well.
Keep the soil reasonably moist, especially in dry periods. Rooting will normally occur during the growing season.
In autumn, sever the layered stem from the parent plant so that the new plant can .accustom itself to an independent existence.
About three to four weeks later, cut off the growing tip to encourage the roots to establish. Pot up or plant out the layer and label it. If rooting is not well advanced by autumn, leave the layer to establish for a further year before lifting and transplanting it.
WAYS TO GIRDLE A STEM
WAYS TO GIRDLE A STEM
Remove a ring of bark, about ^in wide, from round the stem, using a sharp knife.
Tighten a piece of copper wire round the stem. Twist it finger tight.
Make an angled cut halfway through the stem. Keep the cut surfaces apart with a matchstick.
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