In gardening layering is used mainly for those shrubs that are not easy to propagate by cuttings' or grafting. Layering may be carried out either on the spot where the shrub is growing or else in a special bed to which the shrub to be increased is transferred. One advantage of the latter is that it is possible to prepare a soil mixture suitable for propagation, i.e. a lighter, sandy soil, and that the shrubs can be spaced far enough apart. Young one-year shoots root best.
For that reason, if the shrub does riot have a sufficient number of long, one-year shoots close to the base it must first be cut back so that it produces new young shoots.
Some seeds, even though stratified, will not germinate until the spring of the second year, e.g. the cornelian cherry, sometimes also the bladdernut, dogwood, wayfaring tree, English holly, staghorn sumach, etc. Such seeds should be stratified another year and in spring the pots in which they are stored should be put out in a shady spot and sunk in peat halfway to their rims, the peat being watered regularly to keep the substratum and seeds from drying out. In spring the seeds are sown either into a frame or in pots filled with a mixture of equal parts loam, peat and sand.
The seeds should be covered with a layer of soil one to two times their own thickness. For instance rhododendron seeds should be covered with a layer about 1 mm thick, those of the golden rain with a 5 mm layer, the bladdernut with a 10 mm layer, etc. The best temperature for seed germination is 16C - 20C. The seeds must be kept moist at all times, preferably with a fine rose can so that they are not washed out.
A similar method, known as stooling, is used to increase choice varieties of the hazel or to produce a greater quantity of rootstocks for budding or grafting fruit trees. Shrubs to be increased are cut back close to the ground in early spring so that they will put out as many shoots as possible. As these shoots grow they arc covered with a mound of soil up to about 30 centimetres high. During the summer the shoots put forth new roots and in the autumn the soil is removed and the rooted shoots are cut away from the parent shrub and planted out. This method is sometimes used to propagate certain varieties and species of Philadelphus, Deulzia, Hydrangea, and, Syringa.
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