It is agreed on all hands, that nothing contributes more to the preserving of the soil of a garden in good condition, than exposing it as often as possible to the action of the sun and air. It is a rule, therefore, that garden ground, when not in crop, should regularly be dug rough, or if possible ridged up, and left in that state to the influence of the at mosphere. if it be allowed both a winter and a summer fallow, the oftener a new surface is exposed the better ; after it has lain ridged up during winter, therefore, repeat ed diggings are given in the spring and summer months. Whether some noxious matter be exhaled, or some ferti lizing substance be imbibed, or what may be the precise nature of the operation that goes on, we do not here inquire. The fact is certain, that aeration, as it is sometimes called, is of the greatest advantage to garden soils.
45. It has been already remarked, that it is desirable to have soils of different quality in the garden. One of the most generally desired is what is called mould, by which is meant a soil in which vegetable earth predominates. Such as is of a bright Chesnut colour is preferred : it is usually styled by gardeners, hazelly mould, or hazelly loam, from being of the colour of the hazel nut. The characters of the best mould, according to Miller, is, that " it cuts like but ter, does not stick obstinately, but is short, tolerably light, breaking into small clods, is sweet, well tempered, without crusting or chapping in dry weather, or turning to mortar in wet." It should be so open, as not to stick to the spade or the fingers after a shower of rain. Dark grey and rus set-coloured moulds are likewise considered good ; ash coloured are commonly bad ; yellowish red still worse. Good moulds, after being broke up by the spade, or after rain, if the surface have been recently dug or hoed, emit rather a pleasant smell. What are called brick moulds, or looms, are much esteemed, both by the gardener and the florist, as auxiliaries to mix with other soils.
For some purposes a sandy soil is wanted. In this case, either the surface sand, from a sandy pasture, is alone used, as it contains a considerable portion of vege table matter, or, if pure sea or river sand be employed, light rich mould, nearly in the proportion of one-half, is mixed along with it. For a very great number of plants, particularly in the flower garden, an excellent soil is to be found in the turf of old pastures, and the earth which adheres to the turf to the depth of six or eight inches, mixed with a portion of cow and horse dung in a rotten state, laid together in a heap for at least a year, and fre quently turned over. This is a compost, and naturally
leads us to speak more particularly on the subject of manures.
Alan uses.
46. Many authors have treated of manures, and given theories of their beneficial action ; Fordyce, Hunter, Cullen, Ingenhousz, Senebier, and others. The learned Kirwan wrote a separate essay on this subject. In this work of Mr Kirwan, and in the more recent publication of Sir Humphry Davy., may be found all the informa tion on the matter that is to be obtained by reading. To enter fully on an account of manures, or the theory of their action, would here be out of place. Besides, manures in general have already been treated of in a former part of this work, (See vol. i. art. AGRICULTURE) ; and the remarks here made, shall be confined to manures considered as particularly applicable to gardens.
47. It is now an established fact in practical gardening, that for the greater number of culinary plants, and for all fruit trees and flowers, composts or compound manures are far preferable to simple dungs, and that till the latter be completely rotted, they should not in any case be suf fered to touch the roots of the plants. Even composts should not be too rich. Trees especially are very apt to be injured by the injudicious and excessive use of manure. A very rich compost will stimulate them for a few years to preternatural exertion ; but, as remarked by Mr Knight, will in all probability become the source of disease and of early decay. A very good practical gar dener, Mr David Weighton, recommends, for cold clayey land, a compost made up in the following proportions : three parts light mould ; one part rotten stable dung ; one part sharp sand ; one part coal ashes ; half a part lime ; with a Small proportion, perhaps an eighth, of pigeon's or sheep's dung. For a light sandy soil, the following are the ingredients and proportions : to two parts of the natural soil, three parts of pond earth, or the scourings of ditches, and three of strong loamy earth ; one part of clay, nr rather clay-marl, if it can be got ; and two parts of stable or cow-house dung.
In the opinion of some gardeners, the best mode of ap plying compost manures is, to trench deep, and put com post in the bottom, to the thickness perhaps of eight inches ; then to lay on the old garden soil, and to cover the whole with compost to the depth of some inches. In this way, the old or worn out soil is placed in the middle, and is exposed to the effluvia which may arise from the lower stratum, and at the same time is incorporated, by digging, with the upper.