Grafting.—This takes place outdoors from March to May, at the earlier time for deciduous trees and shrubs, and later on for evergreens. The actual time depends upon the season.
Where seed is not expressly mentioned below, it must be understood that this is the natural, and in many cases the best, way to propagate.
The following trees can only be raised from seed to do any good afterwards, though a few of them will throw up suckers, which can be taken off and replanted: Æsculus (Chestnut), Ailantus, Alnus (Alder), Arbutus, Betula (Birch), Carpinus (Hornbeam), Carya (Hickory), Castanea (Sweet Chestnut), Celtis (Nettle tree), Fagus (Beech), Fraxinus (Ash), Gleditschia (Honey Locust), Juglans (Walnut), Laburnum, Liquidambar, Morus (Mulberry), Prunus, Pyrus, Quercus (Oak), Sophora, Ulmus (Elm), and Zelkova. The varieties of any species of the above, and, in fact, of nearly all hardy trees, must be budded or grafted on the species they are forms of, but an exotic species should never be worked on the native representative of the genus—e.g. Æsculus flava should not be budded on the Common Horse Chestnut, as the latter is far too strong a stock for the smaller-growing Æsculus.
Acer (Maple) and Tilia (Lime or Linden) can be raised from seeds or by layering, the Lime especially being largely propagated from layers, which soon form strong young trees. The varieties of Maple are best worked on stocks of the species they belong to.
Cratægus (Thorn), Catalpa, and Robinia (Locust tree), can be raised from suckers or root-cuttings, if seeds cannot be got. Any of their varieties are usually budded or grafted on stocks of the parent species.
Ilex (Holly), Magnolia, Populus (Poplar), Platanus (Plane), and Salix (Willow). The Holly is easily raised from cuttings and layers, the second roots readily when layered, and the latter three are propagated in large quantities by winter cuttings. The White Poplar (Populus alba) is an exception, as this can only be increased by root-cuttings.
Increasing Hardy Shrubs
The best of our hardy flowering shrubs are grouped under seven natural orders, and a knowledge of the order to which a plant belongs is in most cases a guide to its propagation, as the majority of the species contained in an order are, as a rule, increased by the same methods.
Berberideæ.—This contains Akebia and Berberis, which are propagated by seeds, cuttings, or layers. Berberis stenophylla and B. Neuberti do not come true from seed, so that one or both of the other methods mentioned above must be adopted.
Leguminosæ.—In this order such genera as Cytisus (Broom), Genista (Rock Broom), Spartium (Spanish Broom), Ononis, Indigofera, Colutea (Bladder Senna), Caragana (Siberian Pea tree), and Cercis (Judas tree) should be raised from seed, which is the quickest and best method of propagation. Cuttings of certain forms of Cytisus and Genista will root readily, but the plants will sometimes die off just as they have attained flowering size. Ulex (Furze, Whin, or Gorse) is propagated by seeds or cuttings, and Wistarias by seeds or by layering.