184 VEGETABLE FORCING 
rels or small frames placed over the asparagus crowns. 
The top of the barrel may be covered with canvas or 
boards to conserve the heat. 
Ordinary coldframes placed over the beds and covered 
with glass sash will advance the crop much earlier and 
more rapidly in the spring than if it is left without cover- 
ing. This method is used to some extent by market 
gardeners. Additional heat may be furnished by banking 
the frames with hot manure, or a coil of steam or hot 
water pipes may be placed in the frame. 
Hot manure is sometimes placed over the beds early 
in the spring and allowed to remain until the shoots 
start, after which it is removed. This method cannot be 
used too early in the spring without taking risks of losses 
from freezing. 
European gardeners and perhaps a few American 
growers force asparagus by plowing or digging a trench 
midway between two rows. The soil is thrown over the 
rows of asparagus and the trenches are filled with hot 
manure. Sometimes such trenches are lined with brick, 
with passageways to the asparagus rows, thus making 
them permanent. Steam pipes may be placed in the 
tunnels, with or without manure. This plan does not 
appeal to American gardeners. 
Whitten, of the Missouri Station, conducted an interest- 
ing experiment in forcing permanent beds by steaming. 
Trenches were made between the rows and covered with 
12-inch boards which rested on 4-inch blocks placed 
along either side of the trenches. This formed tunnels 
between the rows through which hot steam was con- 
ducted. To guard against the escaping of steam, 2 or 3 
inches of soil was placed over the boards and the entire 
plantation was covered with 5 or 6 inches of horse ma- 
nure. The following data regarding the experiment are 
quoted from Bulletin 48 of the Missouri Station: 
“To conduct the steam a 1%4-inch pipe was carried above ground 
from the boiler to one end of the central tunnel, a distance of 185 
