Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/244

232 232 HORTICULTURE [SOILS. necessary in the cases of most plants cultivated in a high temperature ; but the amount varies of course in different cases, and this presents one of the principal difficulties in the management of what is called a mixed collection, whether of stove or greenhouse plants. In the case of fruits, where a house is mostly devoted to one subject, whether grapes, peaches, pines, or melons, the requisite conditions can be more readily secured. The instrument with which the amount of moisture present in the atmo sphere is measured is the hygrometer. The two hygro meters most generally used are Daniell s and the dry and wet bulb, the former a more delicate instrument, best adapted for scientific observations, the latter a simpler instrument, better adapted for horticultural purposes, because requiring less delicate manipulation. It consists of two thermometers mounted on one frame, the readings of which when uncovered should correspond. One bulb is left uncovered, the other is covered with muslin, and a few threads of cotton, with their other ends immersed in water, keep it constantly moist. The temperature is lowered by the evaporation from the moistened bulb, and the difference in the readings of the two thermometers shows the degres of dryness. Mr Glaisher s instructions, which accompany the set of hygrometrical tables published by him, will be found of great assistance by every one making use of this instrument. Ill, Garden Materials and Appliances. 18. Soils and Composts. The principal soils used in gardens, either alone, or mixed to form what are called composts, are loam, sand, peat, leaf-mould, and various mixtures and combinations of these made up to suit the different subjects under cultivation. Loam is the staple soil for the gardener ; it is not only used extensively in the pure and simple state, but enters into most of the composts prepared specially for his plants. For garden purposes loam should be rather unctuous or soapy to the touch when moderately dry, not clinging nor adhesive, and should readily crumble when a compressed handful is thrown on the ground. If it clings together closely it is too heavy and requires amelioration by the admixture of gritty material ; if it has little or no cohesion when squeezed tightly in the hand, it is too light, and needs to be improved by the addition of heavier or clayey material. Sound friable loam cut one sod deep from the surface of a pasture, and stacked up for twelve months in a heap or ridge, is invaluable to the gardener. When employed for making vine borders, loam of a somewhat heavier nature can be used with advantage, on account of the porous materials which should accompany it. For stone fruits a calcareous loam is best ; indeed, for these subjects a rich calcareous loam used in a pure and simple state cannot be surpassed. Somewhat heavy loams are best for potting pine apples, for melons and strawberries, and may be used with the addition of manures only; but for ornamental plants a loam of a somewhat freer texture is preferable and mire pleasant to work. Loam which con tains much red matter (iron) should be avoided. Sand is by itself of little value except for striking cuttings, for which purpose fine clem sharp silver sand is the best; and a somewhat coarser kind, if it is gritty, is to be preferred to the comminuted sands which contain a large proportion of earthy matter. River sand and the sharp grit washed up sometimes by the road side are excellent materials for laying around choice bulbs at planting time to prevent contact with earth which is perhaps manure-tainted. Sea sand may be advantageously used both for propagating purposes and for mixing in composts. For the growth of pot plants sand is an essential part of most composts, in order to give them the needful porosity to carry off all excess of moisture from the roots. If the finer earthy sands only are obtainable, they must be rendered sharper by washing away the earthy particles. Washed sand is best for all plants like heaths, which need a pure and lasting compost. Peat soil is largely employed for the culture of American plants, as rhododendrons, azaleas, heaths, &c. In districts where heather and gritty soil predominate, the peat soil is poor and unprofitable, but selections from both the heathy and the richer peat soils, collected with judgment, and stored in a dry part of the compost yard, are essential ingredients in the cultivation of many choice pot plants, such as the Cape heaths and many of the Australian plants. Most monocotyledons do well in peat, even if they do not absolutely require it. Leaf-mould is eminently suited for the growth of many free-growing plants, especially when it has been mixed with stable manure and has been subjected to fermentation for the formation of hot beds. In any state most plants feed greedily upon it, and when pure or free from decaying wood or sticks it is a very safe ingredient in composts ; but it is so liable to generate fungus, and the mycelium or spawn of certain fungi is so injurious to the roots of trees, attacking them if at all sickly or weakened by drought, that many cultivators prefer not to mix leaf-mould with the soil used for permanent plants, as peaches or choice ornamental trees. For quick growing plants, however, as for example most annuals cultivated in pots, such as balsams, cockscombs, globe-amaranths, and the like, for cucumbers, and for young soft-wooded plants generally, it is exceedingly useful, both by preventing the consolidation of the soil and as a manure. The accumulations of light earth formed on the surface in woods where the leaves fall and decay annually are leaf- mould of the finest quality. The material known as cocoa-nut fibre refuse is analo gous to leaf soil, and may be employed for similar purposes. It should be mixed with gritty matter to favour the passage of water, and indeed requires to be so mixed when in an advanced stage of decay, in order to prevent its collapse into a close pasty mass. This cocoa-nut refuse is also a useful light material into which to plunge pots containing plants, as a preservative of the roots from the drying effects of the sun or the chilling effects of frost. Composts are mixtures of the foregoing ingredients in Com- varying proportions, and in combination with manures if P ost * necessary, so as to suit particular plants or classes of plants. The chief point to be borne in mind in making these mix tures is not to combine in the same compost any bodies that are antagonistic in their nature, as for example lime and ammonia. In making up composts for pot plants, the fibrous portion should not be removed by sifting, except for small sized pots, but the turfy portions should be broken up by hand and distributed in smaller or larger lumps throughout the mass. When sifting is had recourse to, the fibrous matter should be rubbed through the meshes of the sieve along with the earthy particles. Before being used the turfy ingredients of composts should lie together in a heap only long enough for the roots of the herbage to die, not to decompose. 19. Manures. These are of two classes, organic and Mamu inorganic the former being of animal and vegetable, the latter of mineral origin. Farm-yard manure consists of the mixed dung of horses and Organ cattle thrown together, and more or less soaked with liquid drain- manui ings of the stable or byre. It is no doubt the finest stimulant for the growth of plants, and that most adapted to restore the fertile elements which the plants have abstracted from exhausted soils. This manure is best fitted for garden use when in a moderately fermented state. Horse dung is generally the principal ingredient in all hot bed manure ; and, in its partially decomposed state, as afforded by exhausted hot beds, it is well adapted for garden use. It is most