222 



CASSELL'S POPULAR GARDENING. 



The name of pit suggests the idea of a structure 

 or place partially under-ground. This was so gene- 

 rally recognised in the older pits that the major 

 portion of them were under-ground. Sunken pits 

 are warmer than those partially or wholly ahove- 

 ground. The earth is partially frost-proof in our 

 climate, at least a very little straw litter around the 

 pit makes it so to aU intents and purposes. The soil 

 even becomes a source of warmth to the pit, as its 

 average temperature is ahout 45°. 



Sunken pits were also less exposed to wind and 

 weather, and the surface of the glass far more easily 

 covered in severe weather, than those wholly or in 

 part ahove-ground. With the solid earth as a hut- 

 tress aU round, less material is needed for their con- 

 struction than for ahove-ground pits. Against these 

 substantial advantages of cheapness of first cost, the 

 utilisation of the natural and, compared with the air, 

 uniform warmth of the earth, and greater facility of 

 managing and working sunken pits, there are the 

 dangers and difficulties of dampness — ^the deeper the 

 pits the damper ; and though thorough drainage of 

 the base, careful and peculiar construction of the 

 side walla, skilful ventilation, and artificial heating 

 do much to vanquish or diminish the evils of damp, 

 no doubt the prevailing and destructive tendency of 

 the latter in deep pits did much to raise them nearer, 

 and in not a few instances place them upon or even 

 above the ground surface. Nor is this to be won- 

 dered at, as for one plant killed by cold in pits, a 

 hundred — ^it may be a thousand — have been crippled, 

 disfigured, or destroyed by damp. 



Hence, though deeply-sunk pits are stiU to be 

 found, and in not a few cases, and in exposed locali- 

 ties, these prove the best of all pits, yet so general 

 has the raising of pits nearer to the surface become, 

 and so common are those on the surface, that the idea 

 of a sunken place is no longer essentially identified 

 with pits. Any structure with stable sides and a 

 movable glass roof may be called a pit. Even this 

 description may be held to be imperfect, for not a few 

 pits have fixed roofs. Generally, however, pits are 

 covered with glass lights ; the latter are movable, 

 and access is had to the plants through the roof 

 rather than through the ends or sides. Pits with 

 fixed lights and doors in the ends are transformed 

 into houses, whatever they may be called. 



Wooden pits, again, differ from frames in being 

 fixed by stakes driven into the ground. Neither 

 sides nor ends can be lifted off without the nails or 

 screws that fix them to the ground being first with- 

 drawn. 



Wooden pits, however, once so common, arc now 

 out of fashion. Formed of two layers, and the in- 

 terstices of six inches or a foot between the boards 

 filled in with sawdust, tan, chaff, or other non-con- 



ducting material, they were at once dry and weather- 

 proof. Such pits were even used iil France for Pine- 



grOWLQg. 



The walls of pits are mostly built now of stone, 

 concrete, turf, bricks ; even iron has been tried for 

 both pits and frames. The three first are not liked, 

 and iron is very seldom used. Turf is efficient 

 against all weather severities in our climate, but it 

 is too perishable for permanent pits, though most 

 useful for temporary ones for the protection of 

 semi-hardy plants, vegetables, salads, &c., in winter. 

 Turves of fibrous grass or peat, from two to three 

 inches thick, and from fifteen to eighteen inches 

 wide, will form a temporary frost-proof — as fer as 

 the walls are concerned — pit that wiU prove most 

 useful for an infinite variety of purposes in most 

 gardens. It may either be covered with glass lights, 

 laid on rafters let into the upper or finishing rows 

 of the turf, or with opaque frames of canvas, oiled 

 calico, or reedS. Such rough-and-ready structures 

 are invaluable for the temporary protection of 

 flower-garden — or what are technically known as 

 bedding — ^plants in the spring and early summer 

 months. 



But bricks are at once the most popular, useful, 

 and efficient of all materials for building pits. A 

 brick wall, fourteen inches thick, in a vertical posi- 

 tion is practically frost-proof in our climate. For 

 pits of smaller size, brick walls four and a half or 

 nine inches in thickness will suffice. In the case of 

 very large pits, such as are often used for Pine-cul- 

 ture, from seven to nine feet high at back, and from 

 five to seven feet high in front, with covering lights 

 eight or twelve feet long, eighteen or twenty-two- 

 inch walls will not prove excessive for the weight 

 and wear-and-tear to which they will be subjected. 

 The strain is far heavier and more constant on the 

 walls of pits than on those of houses, owing to the 

 constant motion and friction of the movable lights. 

 Hence the necessity of specially thick and strong 

 walls for large pits, though the tendency of the day 

 is to limit and even reduce the size of pits, and con- 

 vert the larger ones already in existence into houses 

 with fixed roofs. 



The walls of pits are also frequently left hollow. 

 The practice not only economises material, but pro- 

 bably strengthens the walls at the same time, while 

 it is certain that the enclosed air is a less powerful 

 conductor of caloric than solid bricks. Hence the 

 common saying that hollow walls are warmer than 

 solid walls is strictly true, though not expressed 

 with scientific accuracy. 



For all common-sized pits, nine and fourteen-inch 

 brick walls are sufficiently thick and strong. Four- 

 and-a-half-inch walls should never be used, for un- 

 less fortified by a free use of fourteen-inch pillars at 



