203. In general it may be remarked, that what is called forcing is the more perfectly performed in proportion as less forcing or violence is employed. All the operations of nature are gradual ; and a good gardener will always follow these as the safest examples. He will never wil lingly apply artificial heat before buds have naturally bwoln ; he will then increase the temperature gradually for some weeks ; he will, in particular, guard against any sudden decrease of warmth, it being most necessary to wards success, to continue the course of vegetation unin terruptedly, through foliation, inflorescence, and fructifi cation. In all kinds of forcing, it is of importance that free admission of air be given according to the state of the atmosphere ; and it too should be given and withdrawn by degrees, especially in the early and cold time of the year : the sashes, or the ventilators, may, for instance, be par tially opened by &•in the morning, top air being given be fore front air ; full air may he allowed about 10 ; a reduc tion should take place before 3 P. M., and the whole he closed between 4 and 5, according to the season and other circumstances.
We shall now proceed to notice the peach-house, cher ry-house, vinery, and fig-house, in succession ; then the pine-stove and appendages ; and the orangery. Here we shall take occasion to introduce a short description of the magnificent and commodious suite of hot-houses at Dal meny Park, near Edinburgh, plans and elevations of which we are enabled to lay before the reader ; and we shall sub join some account or improvements which have lately been adopted or proposed in this branch of horticulture. The cultivation of the melon, being allied to that of the cucumber, will lead us to the kitchen-garden.
The Peach-House.
204. A peach-house intended to be commanded by one furnace, is commonly made about 40 feet long, 10 or 12 wide, and about 14 in height. It has sometimes no upright glass in front ; merely a parapet 18 inches high, upon which the rafters immediately rest. In some places the peach and nectarine trees are trained to a trellis next to the glass, none being placed on the back wall ; in others the trees are trained only to the wall, or to a trellis placed against it ; but in the greater number of cases, small trees are trained nearly half way up the glass roof, and at the same time others of full size are placed against the back. wall. The flue passes in front, but at some distance from the parapet, and is returned also at some distance from the back wall; so that both flues taken together, with the space between them, occupy nearly the centre of the house. The.
old practice of having the back wall itself fined, is now discontinued, standing flues within the house being found preferable. Both parapet and flues rest on pillars, so as to allow the roots of the trees free egress to the border on the outside of the house. Heady or forced fruit be wanted, the house is made narrower and shorter, so as to give a greater command of temperature. In such houses, either three or four dwarf trees, with intermediate riders, are planted ; the riders being taken out at the end of four years at farthest. When small trees are also trained in front, three are commonly sufficient there, or nine or ten trees in all. Fire-heat is generally applied about the mid dle of February, the temperature being for a time kept at and afterwards gradually increased to 56° or 55" Fahr. The temperature is regulated by a thermometer every morning and evening ; during sunshine, air is ad mitted, to keep down the heat, as near as possible, to the average point. Trees thus forced, generally show their blossoms in March. While in flower and till the fruit be set, gentle steaming is practised, by sprinkling water on the surface of the warm flues. After this, washing the foliage with the garden engine is found very conducive to the health of the plants. When the stones of the fruit are formed, the temperature is raised to about 60°, and the crop is thinned, if thought necessary. Water is now liberally applied to the border. After May, little fire-heat is given, and air is very freely admitted through the day.
Mr Knight strongly recommends the exposing the fruit, when ripening, to the full influence of the sun in warm and bright days, and covering it with the glass roof during cold night air or rains. He has, in the London Horticultural Transactions, vol. i. p. 199, described an improved peach house. The angle of the roof is only 28° in Lat. 52°. In order that the lights may be moved to the required extent with facility, they are made short, and divided in the mid dle. The back wall does not exceed nine feet high. Two rows of trees are planted ; one in front, trained on an al most horizontal or very slightly inclined trellis ; and the other on the back wall. The house is 50 feet long, bet commanded by a single furnace.
The mull displacing of useless buds and spray, and lay ing in of new shoots, are operations which must, of course, be attended to, as in the managemeet of peach and necta rine trees on the open wall.