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 43 of the Missouri Station : 



"To conduct the steam a 1^-inch pipe was carried above ground 

 from the boiler to one end of the central tunnel, a distance of 185 



