FORCING IN THE FIELD
Forcing asparagus where it is grown in the field has a twofold advantage over removing the roots to a warm place. First, it saves the trouble and expense of transplanting them, which must be done with much care; and, second, it saves the plants from being ruined by the forcing process. Plants forced in the field where they grow will, if given good care, regain their vigor in a season or two, and may be used again for forcing. By this latter method a better quality and a larger quantity of marketable asparagus is also secured.
Various means have been devised to force asparagus in the field, where it is so well established that it continues growth in the summer as though it had not been forced the previous winter. A simple and rather common method of accomplishing this is to place barrels over clumps of asparagus very early in the spring and pile fermenting manure about them, the warmth from the manure forcing the shoots into rapid growth. When the forcing season is over and the danger from frost is past the barrels are removed, and the plants continue growth in the open air. Sometimes asparagus is forced by placing frames, covered with sash, over the plants in the field, the rows of asparagus being set rather close together. This is considered a very profitable method by many market gardeners. Another method of forcing asparagus in the field is to dig ditches between the rows and fill them with fermenting manure. The surface of the bed may also be mulched with manure. The latter plan is extensively practiced by French market gardeners.
At the beginning of November the pathways between the beds of asparagus are dug up about two feet in depth and width. The soil coming from the pathway is divided very carefully and put about eight inches thick on the surface of the bed. The trench is filled up with fresh stable manure, not litter, and frames are placed on the bed. The manure should rise as high as the top of the frames and the lights be entirely covered with mats and litter to prevent the heat accumulating in the frame from escaping. In about two or three weeks the asparagus begins to show itself on the surface of the bed. Many market gardeners cover the whole of the bed inside the frames to a thickness of three or four inches with manure, to force the vegetation more quickly; but in this case the manure must be removed when the asparagus begins to shoot. When the shoots are about three inches out of the ground they may be cut. The mats must be taken off in the daytime, but the heat must be well kept up, else the roots and buds will fail to push. The beds are forced every second year only. The gathering of the asparagus may continue for about two months but no longer, or the plantation would be injured. When the gathering is over the frames are taken away, and the soil which was dug up from the alleys is put back again.
An ingenious method of forcing asparagus in the field by means of shallow tunnels was devised and successfully carried out by Prof. J. C. Whitten, at the Missouri Experiment Station, who gives the following account in Bulletin No. 43:
"The field selected for the experiment was planted to asparagus about ten years ago. The plants were in fair vigor, though of a small variety. The first section forced embraced six rows, four feet apart, and fifty feet long. Fig. 35 shows this section with one tunnel uncovered. Trenches were first made between the rows. This was done by plowing between them, twice in a place, throwing the furrows on the plants so as to cover each row with two furrows of loose earth. These trenches between the rows were then made uniform by means of the spade. When finished they were three or four inches lower than the crowns of asparagus in the adjacent rows. These trenches were then covered with twelve-inch boards, which rested on four-inch blocks, placed at frequent intervals along either side of the trenches. This formed tunnels between the rows for conducting the steam. To guard against the steam's escaping, two or three inches of soil was placed over the boards, and the asparagus patch was then covered with five or six inches of horse manure. This covering was to prevent the heat from escaping from the soil too rapidly. It was then ready for the steam to be turned into the tunnels.
FIG. 35—TUNNEL THROUGH THE ROWS OF ASPARAGUS FOR FORCING STEAM THROUGH THE SOIL