Plant Propagation: Layering Method
This is another easy and sure way of propagating a number of flowering and fruiting plants to ensure that they are the same as the parent. Layering occurs naturally in many plants, and is the term used to describe the rooting of a stem while it is still attached to the parent plant. The ‘runners’ of the strawberry and the tip-rooting of loganberry and blackberry are the well-known examples. Naturalalso occurs with large trees and shrubs, and examples can be seen in public parks and gardens. Beeches and horse chestnuts with low branches sweeping the ground will layer themselves. Generally the rubbing of the branch against the ground causes an injury to the bark. Then, from the healing of the wound and contact with the , roots form to anchor the branch, which eventually grows to become a secondary tree beside the parent. The layering of and other ornamental shrubs is sometimes done into large boxes of prepared soil placed beneath the branches to be layered. The advantage of a box is that once the layer is rooted and severed from the parent plant it can be moved without disturbing the new roots.
Other plants, particularly strawberries and clematis, are layered by pegging the growth into pots filled with gritty soil and plunged into the ground near to the parent plant. Loganberries and blackberries can be treated in the same way.
Border or hardy carnations are propagated by layering. The operation is carried out towards the end of July and during August, except in the north of the British Isles where July is the best time. It is important to remember that it is the new season’s growth, or non-flowering shoots, that are layered, and that strong plants are needed to withstand the winter.
If layers are ‘put down’ too early they may grow too tall and soft, especially during a wet season and, following trans-planting in early autumn, such plants can be damaged by the first frost.
As long as care is taken, layering carnations or any other type of plant is quite as easy asand, as the layers are still attached to the parent plant, they are more sure of rooting.
A good sharp knife with a thin blade is needed, as well as a trowel, a hand-fork, and a supply of layering pins or pegs made from 6-in. lengths of galvanized wire bent double and shaped like a hair-pin. Good fresh soil made up with a mixture of loam, peat-moss or sifted leaf-soil, sharp sand and pulverized mortar-rubble is also necessary. Theshould be moist, but not so wet that it will bind together when pressed.
After midsummer select a strong, healthy plant with good growth that is free from. Lightly loosen the soil round the plant with the hand-fork, being careful not to disturb or break the roots. Then spread a layer of the prepared compost round the plant to form a ridge or mound 2 or 3 in. higher than the normal soil level, and make it fairly firm. This is particularly necessary if the soil is heavy and inclined to be wet. Arrange the soil so that the growths to be layered can readily be anchored into it. On light soils that are well drained, the use of prepared soil is not so necessary, although it is wise to add some peat-moss or sifted leaf-soil, and incorporate it well with the natural soil. This increases the humus content and is good for the layered plant when the roots are formed. Select the best and most suitably placed shoots and prepare them as follows:
Strip off all leaves from the part of the stem to be put in the soil (usually two or three pairs of leaves are removed). Then with a sharp knife cut into the stem to about half its thickness, just below a joint from which the leaves were removed. Extend the cut up the centre of the stem for about an inch so that a tongue is formed, and trim the end of the tongue if the cut is not clean. Then bring the shoot down, keeping the cut open, and press the tongue into the soil. The whole of the cut portion will thus be in contact with the soil and should be secured there with a layering pin placed below the cut and pressed firmly into the soil. Treat each growth to be layered in the same way and then make sure that the cut portions of the layers are covered with soil. Sprinkle another inch of prepared soil round them and thoroughly moisten, preferably with a watering-can fitted with a fine rose. This watering in is essential because it settles the soil round the layers and gives the final firming.
The method used particularly for layering shrubs, closely copies the natural process. The shoot or branch is bent or twisted where it is to make contact with the soil so that the bark is damaged and the tissue is split. The splitting of the wood checks the flow of sap and causes the formation of callus or healing tissue from which roots will usually emerge. In addition to pegging down the layered shoot or branch it is advisable to secure the tip to a small stake, tying it as nearly as possible in an upright position. This prevents damage to the shoot, makes sure that it grows straight, and prevents it from swinging up into its old position before the roots have formed.
If the weather is hot, watering is necessary, because it is essential that the ridge or mound of soil does not dry out. After about six weeks inspect one of the layers, by gently lifting it to see if roots have formed. Some layers will be in advance of others, but experience will soon help the gardener to decide when plenty of roots are formed. When all the layers are rooted, sever them from the parent plant by cutting the stem between the layer and its parent, but leave the layered plants in position for a time to recover from the severing and to become fully established on their own roots. After a week or so lift the plants and pot them separately in pots varying in size according to the plants, or plant them out into well-prepared soil in a bed or border.
AIR LAYERING WITH POLYTHENE
Air layering in its original form was practised in China centuries ago. A stem or branch was partly severed by making an upward cut from just below a joint, and after a small wedge had been inserted to keep the cut open, sphagnum moss or some other moisture-holding medium was wrapped round and over the cut and fixed with string. If the moss or other material was kept constantly moist, roots eventually grew out into it and, after a while, the air layer was removed and potted separately to provide a separate plant.
In the past various modifications of this method were used in the British Isles, chiefly to propagate greenhouse plants. But the success of air layering depended on the sphagnum moss or other material being kept constantly moist, and this was only possible in greenhouses where the atmosphere was moist and regular attention could be given to syringing and watering. The necessity for constant damping is now no longer a problem if polythene or plastic film is used to surround the layer and its rooting material. Air layering is therefore a method which can be used with every chance of success, particularly for those plants which are difficult to propagate by the usual methods of seeds or.
The best time for air layering depends on the season and to some extent on the locality, but most ornamental shrubs and trees growing in the open should be air layered in April when the sap is rising and flowing freely. Plants growing under glass can be air layered from March to July.
The branch to be air layered should not be too tender or too old. Mature one-year-old wood is the most suitable, but there are exceptions with different kinds of plant. Firm wood is better than pithy wood and should usually be about as thick as an ordinary pencil.
The operation is not difficult to per-form. Make the cut with a good sharp knife, starting just below a leaf stalk or joint and penetrating half-way through the stem, then turning upward for about 1-½ in. Treat the cut surfaces with a hormone or root-promoting substance. Wedge open the cut with a twist of moss. Then pass a tube of polythene over the growing part of the branch, slide it over the cut and secure its lower end with adhesive tape. Pack the tube with moist sphagnum moss that has been broken up until it covers the cut portion and extends several inches above it. Then bind the top of the tube with adhesive tape. Support the layer by tying the layered branch to a bamboo cane or to another nearby branch. Inspect the layer from time to time to make sure that the plastic film is unbroken and that the layer itself is secure. If the sealed layer is airtight, the moss surrounding it will remain moist throughout the season and until roots have formed. When these can be seen through the polythene remove the layer from the parent plant, take the polythene and moss carefully away, and pot the new plant in the usual way. Keep the new plant in a frame or greenhouse until well established, and plant it out in the spring.