Soil Heating Techniques for Forcing Outdoor White Asparagus into Production

ABSTRACT Hot water was circulated in two pipes placed above (AC), beside (BC), and under (UC) the crowns of the asparagus (Asparagus officinalis L.) hybrid cvs. ‘Dariana’, ‘Larac’ and ‘Steline’ to force them into production in winter. An unheated bed of each cultivar was used as control. Raised beds were covered with black plastic mulch to ensure white spears and weed control. The heating system was activated in mid-January for the 1998 harvesting season, mid-December 1998 for the 1999 harvesting season and early January for the 2000 harvesting season. In 1998 and 2000 harvesting seasons, early yield of A grade spears in the UC treatment was significantly different from controls, and the AC and BC treatments which were similar. The total yield of the UC treatment was significantly different from the control and the AC and BC treatments only in 1998. The UC treatment improved the quality of the product in 1998 and 1999 since “B” grade yield, as a percentage of “A” grade yield, appeared to be lowest. ‘Dariana’ consistently had higher total yield than ‘Larac’ and ‘Steline’ in all production years. In 1999, ‘Dariana’ yielded more early “A” grade spears than ‘Larac’ and ‘Steline’.