This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Under this head we include all plants that are herbaceous, technically speaking, whatever their duration, and whether bulbous or fibrous-rooted. At another place we give some short lists and hints to enable possessors of small gardens to select a few species worthy of a place in every garden. The general routine to be observed in the cultivation of herbaceous plants, excluding the strictly alpine species, is simple enough. A rich, deep, well-drained soil, tilled to a good depth, is the first condition. Where the soil is poor and shallow, means must be taken to improve it, for, with a few exceptions, herbaceous perennials require generous treatment. Turfy loam, mixed with leaf-mould and thoroughly rotten stable-clung, will be found the most effective for nearly all poor land. A stiff clay is perhaps the most unmanageable description of soil for a flower garden, as greater difficulty is experienced in working in material to make it freer. In such cases if practicable a spit of the clayey soil should be taken out and replaced by a suitable compost, the surface mould, if any, being kept back and mixed with it. The method of planting will be determined by the taste and requirements of the cultivator. The principal considerations are: size and colour, and flowering-season, and space for the introduction of bedding plants where it is desirable. There should also be some proportion in the relative size of the plants of different species. Free-growing species that soon cover a large space should be kept in check, and the more delicate ones encouraged by special study of their habits and peculiar likings. Thinning out of superfluous stems and supports where needed should always be seen to as soon as needful. The stakes or other supports used should be selected according to the respective heights of the plants, and as much hidden from view as circumstances will permit. If painted green, so much the better, as they are then less striking; but even common hazel or other stakes with the bark on are scarcely noticeable when properly put in. Nothing is more unsightly than the common practice of tying up the stems of a plant like a broom to a single rough stake standing a foot or two higher than the plant itself. One support or more may be necessary according to the habit of the plant, and in no case should they exceed the full-grown plant. Care should be taken to preserve the natural habit of each species. The best material for tying is bast or soft string. Much time is gained by performing this and many other operations as soon as the plants are sufficiently advanced; and not only time in this case, but likewise a better effect. For when plants are neglected, the stems spread out and lean in all directions, so that when they are tied up they remain unsightly for some time, even if they ever assume an elegant appearance, in consequence of the stems being crooked and the leaves twisted.
A large proportion of the perennials in general cultivation are easily propagated either from off-sets, cuttings, or seeds in the open borders; but that is not the case with many of those species which will not bear root-division, and whose seeds are very minute. The familiar Wallflowers, Pansies, Polyanthuses, Monkshood, Columbines, Antirrhinums, Michaelmas Daisy, Scarlet Lychnis, Arabis albida, London Pride, etc, owe, no doubt, some portion of their popularity to the facility with which they are increased. Where, as in the case of Antirrhinum, Polyanthus, Larkspur and Pansy, propagation is usually from seed, this should be thinly sown in beds or patches, not earlier than the middle of March, as it will then quickly germinate and grow with more vigour, and thus form stronger plants, and escape, to a certain extent, the ravages of birds and insects. Propagation by division - the means employed to increase Arabis albida, London Pride, etc. - should be done in winter, whenevei the weather is suitable. The principal hardy bulbous and rhizomatous perennials, such as Irises, Snowdrops, Crocuses, Tulips, Lent-Lilies, etc, also increase rapidly in favourable soil; but this class of plants will be treated of separately, as many of them require exceptional conditions to ensure their complete development.
A few words respecting the raising and treatment of the more delicate species may be useful; but knowledge of the peculiar habits of different plants, and consequent difference in treatment, must be gained by actual experience; and observation will soon supply the clue to proper treatment in most instances. Nearly all of the small-seeded plants, and those whose seeds usually lie dormant for a considerable period, as well as rare or small-growing species, require the shelter of a cold pit to raise them in, and afford them protection until they have attained sufficient strength to be transferred to the open ground. Ordinary frames placed where they will obtain abundance of light will answer all purposes very well. They should be shallow, and have a depth of about six to nine inches of coal-ashes, sand or tan, or other material in the bottom, for plunging the pots in, and thus ensuring effective drainage, so as to prevent the accumulation of water. Coal-ashes are as good as anything for this purpose, as they move freely and are unfavourable to worms, one of the worst scourges in seed-pots. The pots or pans used should have a good layer of sherds in the bottom to ensure perfect drainage, or the soil may soon become sour. For general purposes a compost of free loam, thoroughly rotted leaf-mould, or dung from an old hot-bed, and sufficient sharp sand to keep it from binding, will be found suitable. About one-fourth of leaf-mould or rotten stable dung will be ample, and if the loam be rich, a smaller proportion would suffice. Seeds should be covered with soil according to their size; a layer about their respective thicknesses may be observed as a general rule. Very minute seeds should not be covered at all, merely sown on the surface of the moistened soil, with perhaps a slight sprinkling of sand. A little extra sand on the surface may be recommended for all seed-pots, as it prevents the soil from forming a crust. A little moss, too, is a very good thing to place on the top until the seeds begin to germinate, especially where the seed is near or on the top of the soil, as it secures the surface from being disturbed by watering, and prevents rapid drying. Careful watering, indeed, is of the utmost importance; for while much moisture with a low temperature is fatal to most things, seed-pots should never be allowed to dry up. After a seed has once started into life, its course cannot be interrupted with impunity, and until a plant has made considerable root it is wholly dependent upon surface moisture.
As has alreadv been observed, there is a wide difference in the time occupied in germination, varying from a few days or weeks to twelve months or more, according to the species, and to some extent the age of the seed. The necessity of keeping the pots free from weeds will be obvious; but as these, in many cases, are very difficult to distinguish in a young state from the seedlings it is desirable to raise, we must endeavour to kill all seed that is in the soil before sowing very rare or choice kinds, or those likely to lie dormant for a lengthened period; this may be done by baking, not burning, the mould. The frame should have a thin shading all the time the sun is upon it, and very little ventilation is required until the plants are fairly above ground. It is best to have a second pit or frame to remove the seedlings to as they come up, because they will gradually need more air until they are finally planted out. Thick sowing is to be deprecated for many reasons, but chiefly because overcrowding gives number without constitution or vigour. The course to be pursued after the seedlings have attained a fair size will be determined by the season and the rarity of the species in question. After weeks or months of watching and nursing, it will be better to ensure success by getting them established in pots before turning them out into the open borders. A sharp look-out must be kept after mice, slugs, wood-lice, and other destructive animals and insects.
The management of plants in the beds and borders is so simple that it appears superfluous to add anything to what we have already said. The selection and disposition will vary according to the taste and time of the cultivator, and the extent of his garden. Delicate subjects should be avoided where there is little space and little time to devote to their cultivation. Dead leaves, flower-stems and weeds should be removed as they appear. The surface should be slightly moved by raking or forking, but deep digging is unnecessary, and often destructive. To improve or renovate the soil, a surface dressing of leaf-mould or rotten dung may be applied if desirable; but the better plan is, if the borders have been properly prepared, to leave them alone for a few years, and then partially or wholly renew them, and transplant the whole of the occupants. Liquid manure should always be sparingly used, and reduced to a weak consistency, and only when such subjects as Dahlias and Hollyhocks are introduced is it desirable to resort to it at all for a tolerably fertile soil.
The successful cultivation of strictly alpine plants is a task of much greater difficulty, undertaken only by those who have the needful time and convenience. Many of them require the greatest skill and experience of their natural conditions; and some defy all attempts to keep them alive beyond a season or two. Artificial rockeries are erected with appliances to ensure good drainage and a cool moist atmosphere during the warmer months. And even then it is usual to grow the more susceptible species in pots, and plunge them, so that they may be transferred to a cool pit during the inclement season, when they are liable to damp off from excessive moisture. Nevertheless, there are many of the more vigorous alpine species that will flourish well in any ordinary free soil. It is chiefly the diminutive species, and especially those clothed with hairs, that are the least amenable to the artificial conditions inseparable from culture, and these peculiarities are alluded to in the descriptive portion of this work.