When grapes are forced by artificial heat, probably the best plan is that of the "lean-to" structure shown by the illustrations, Figs. 61, 62, and 63. Fig. 61 gives the plan, which, as in some former engravings, it is not practicable to show on the page at full length; it is accordingly "fractured" portions, as shown by the irregular lines, being taken out of each compartment; the figures give the proper proportion. Fig. 62 is a part of the front elevation, and fig. 63, a section at the division between the two houses. The house is 100 feet long by 16 feet wide, divided into two compartments for early and late forcing, each 50 x 16 feet, and both heated by one boiler with valves in the furnace pit to shut off and taps to draw the water from the pipes not in use; a matter to be looked to when vineries are not in use, for if the water is not drawn out of the pipes it may freeze and burst them. When grapes are to be forced, it is essential that a sufficient covering of manure or leaves be placed on the border to prevent frost from reaching the roots, as to apply heat to the vines inside while the roots are frozen, would seriously injure them. For very early forcing, when the vines are started as early as January, it is usual not only to put covering enough to secure from frost, but also to slightly ferment, so as to throw some warmth into the border. No matter at what season the grapery is started for forcing, the temperature should not run over 50° or 55° at night, with a day temperature of 10° or 15° higher, increasing 10° when the buds have opened, which will be in four or five weeks from the time of starting. In five or six weeks the fruit will be set and the temperature is to be raised 10° more. In forcing, moisture is of equal importance with heat, for if this is not attended to, you may expect red-spiders and thrips, and then all your labor may be in vain; to keep up this moisture, tanks are usually placed on the hot-water pipes for graperies, and these are kept filled with water, keeping up a continued evaporation, except at the time the vines are in flower; it should be then discontinued until the fruit is set. When there is no such arrangement for evaporation, dash water over the floors and use the syringe. To secure fine berries and bunches, one-third of the berries should be thinned out when of the size of peas, using scissors made for this purpose.
Fig. 61.- Plan Of Forcing Grapery.
Fig. 68. - Section Of Forcing Graphry.