RHUBARB 193 
deep coldframes are then placed over them. The plant- 
ing distances must be such as to best utilize space in the 
frames. If the frames are 6 feet wide, there may be 
three rows of plants running lengthwise in them, and the 
plants may be 2 feet apart or even less than that if the 
beds are given special care previous to the forcing period, 
so that they will grow strong roots. 
Trenches heated by steam or hot manure, as explained 
on page 184, may also be used, but it is doubtful whether 
the plan is practicable when labor costs as much as it 
does in the United States. 
In the Boston district, cheap permanent benches are 
built over the rhubarb plantations, where the plants are 
set about 2 feet apart each way. Such houses ordinarily 
contain board walls. There are wooden rafters to sup- 
port hotbed sash, placed to make either an even-span or a 
shed form of roof. For use in winter, a few coils of steam 
or hot water pipes are installed for the maintenance of 
proper temperature. For use early in the spring, no heat 
will be required in addition to that supplied by the rays 
of the sun on the glass sash. At the close of the period 
Fig. 63.—Rhubarb growing in coal ashes in an ordinary cellar. 
