CHAPTER VII. Propagation of Hardy Trees and Shrubs

PROPAGATION OF HARDY TREES AND SHRUBS

If we were to take many books about trees and shrubs or general gardening as a guide, one might be led to think that only one way of increasing a tree or shrub existed, and that by grafting; but, as we have pointed out elsewhere, it is a mischievous practice when indiscriminately applied. It is not contended by this that grafting and budding are utterly needless, as in many instances these methods may be rightly adopted, but the four natural ways of increase are by layers, seeds, suckers, and cuttings. Many trees and shrubs are much better when grafted upon other stocks.

Of these, practise seed-raising whenever possible; but if seeds cannot be procured, then adopt other ways, and the man is wise who tries to keep a plant on its own roots. Neither budding nor grafting should be resorted to, unless other means fail absolutely. When standard trees cannot be got true from seed, budding or grafting must be practised, and the evils of these methods of propagation are not so pronounced in such cases as with dwarf plants. With the former, suckers, or growths from the stock, are easily seen as soon as they appear, but with dwarf plants a perfect forest of suckers may seriously weaken the plant before they are noticed.

SEEDS.--These can be sown at almost any time, but the spring is the best, as those which germinate quickly have time to form strong young plants before the following winter. Some take two years to come up, and should be left in the ground. This refers more to seeds sown outdoors, and few hardy trees and shrubs require heat to assist germination. When sown in the open the beds should be made on a fairly rich, moist piece of ground, protected from cold winds, but fully exposed to the sun. After the seeds are sown, cover them with light tiffany shading, fir branches, or heather, but the first is best, as it is easily removed to attend to the bed. Conifers especially should be sown in beds, whether indoors or outdoors, as pot-culture results in the roots taking the shape of the pot, and never afterwards recovering from their cramped condition. It must be remembered, however, that varieties cannot be depended upon to come true from seed, though by careful selection for a few years many varieties will almost reproduce the characteristics of the parents. Hybrids, such as Berberis stenophylla, Hypericum moserianum, and many others, also do not come true from seed, so that cuttings, layers, or division of the old plants must be the practice chosen.

SUCKERS.--Plants which throw up suckers from the base, or below the ground-line, are easily propagated by detaching these suckers in winter with a portion of root. They will grow away readily, and soon form good trees or shrubs as the case may be.

CUTTINGS.--Nearly all the hardy shrubs, and a small proportion of hardy trees also, can be propagated by cuttings taken at certain times of the year. Summer cuttings are taken during the last two weeks of May and throughout June, the actual time depending on the season, and consist of the young shoots that have grown to a length of 3 to 6 inches. These should be pulled off with a "heel," and inserted in sandy soil in a close frame, with brisk bottom heat. The cuttings should be taken on a dull day, or early in the morning, and kept cool and moist until they are in the frame. A cutting that has flagged is useless, as it never revives. Deciduous flowering shrubs are usually propagated by summer cuttings, which generally root well in a fortnight or less. Autumn cuttings are taken during August and September, and are made from the partially ripened growths of the current year, inserted in sandy soil, in a close frame, without bottom heat. Winter cuttings are made from thoroughly ripened wood at any time between October and March, and are laid in rather thickly in rows outdoors, and only about an inch or less is left above the soil. The majority of our best flowering shrubs are easily increased in this way.

LAYERS.--Excellent trees and shrubs can be got by layers, and they may be laid down at any time of the year; they will be ready for removal in about eighteen months or two years.

BUDDING.--This is done about August, and the same rules apply to trees and shrubs as to Roses, &c.

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.

ROSACEÆ.--This includes Prunus, the shrubby forms of which can, in the majority of cases, be increased by cuttings or layers; Spiræa and Kerria (Jews' Mallow), cuttings of which root readily at almost any time of the year; Exochorda (Pearl Bush), must be raised from seed to do any good; Rubus (Brambles), some of which can be propagated by suckers, and the remainder by pegging the points of the shoots down to form young plants; Rosa (Rose), the species of which should be increased by seeds, cuttings, or layers, though seeds will not always come true, as Roses become hybridised very readily; and Cotoneaster, which are increased by seeds, cuttings, or layers.

SAXIFRAGEÆ.--In this order Hydrangea, Deutzia, Philadelphus (Mock Orange), Escallonia, and Ribes (Flowering Currant) are included. All are easily propagated by cuttings taken in almost any season of the year. With the exception of Hydrangea, which should be struck under glass, all the members of this order root readily outdoors in the winter.

CAPRIFOLIACEÆ.--This order contains such genera as Sambucus (Elder), Viburnum, Lonicera (Honeysuckle), Symphoricarpus (Snowberry tree), Abelia, Leycesteria, and Diervilla (Weigela). All are easily propagated by cuttings or by layering. The cuttings can be taken at almost any time of the year, and root quickly, the young plants attaining a good size by the end of the second year.

ERICACEÆ.--This order includes all the so-called American plants, such as Pernettya, Gaultheria, Leucothoë, Andromeda, Pieris, Zenobia, Erica (Heath), Calluna (Common Heather, Ling), Kalmia, Ledum, Clethra, and Rhododendron (including Azalea). These can all be increased by seeds, layering, and, in addition, the first two by division of the old plants. Erica and Calluna can also be increased by cuttings. Seedlings, of course, make the best plants, but layering is a quicker method, and, in the case of some of the smaller Ericaceæ, one of the easiest. All the Rhododendrons will not root from cuttings, though some of the small-flowered ones strike easily, but practically all may be increased from layers. A few of the showy garden forms cannot be raised from layers, and have to be grafted on stocks of the common R. ponticum or R. catawbiense.

OLEACEÆ.--This includes both deciduous flowering shrubs and ornamental evergreens, such as Syringa (Lilac), Chionanthus (Fringe tree), Jasminum (Jasmine), Forsythia, Ligustrum (Privet), Phillyræa (P. decora (vilmoriniana) is so easily raised from seeds or cuttings that it is foolish to graft it on the common privet), and Osmanthus being represented. The first two are best propagated by seeds or layers, though the named garden Lilac is usually grafted on stocks of the common S. vulgaris, a silly practice. It is a pitiful business keeping down suckers from grafted plants. Ask for Lilacs on their own roots, and much vexation will be saved. A garden should be a place of rest and pleasure, not a hunting-ground for suckers. The other genera are readily raised by cuttings taken at almost any time of the year, or by layering.

Although the above orders include a considerable number of our best shrubs, several plants must be specially mentioned. The Clematis is increased by seeds, cuttings, or layers in the case of the species, but unfortunately the garden forms are usually grafted on C. Viticella or C. Flammula, whereas many can be propagated by cuttings, and practically all will root when layered.

In the absence of seeds the following genera must be propagated by layers, viz., Aucuba, Chimonanthus (Winter Sweet), Halesia (Snowdrop tree), Hamamelis (Witch Hazel), Hippophaë (Sea Buckthorn), and Myrica (Candleberry Myrtle). Cuttings of the first will root readily enough, but never seem to succeed afterwards. The female form of Hippophaë is best raised from layers, as seedlings usually give a large percentage of male plants. Aralia and Rhus (Sumach) are increased by seeds or root-cuttings; Buddleia japonica is best raised from seeds, and the other Buddleias from cuttings; and practically all other hardy shrubs that have not been specially mentioned are easily propagated by seeds, cuttings, or layers, and the majority of them by all three methods.

If it is impossible to increase a tree or shrub by any other means than by the three methods mentioned, then resort to budding or grafting.