Mulch color affects radicchio quality and yield

Interest in the production of the specialty vegetable radicchio (Cichorium intybus L. var. silvestre Bisch.) has increased among vegetable growers in the northeastern United States due to the popularity and consumption of premixed prepared salads. Growing environments with moderate daytime temperature and high light level have been associated with dense, deep red heads. Production problems include the low percentage of plants producing marketable heads and labor costs associated with hand-weeding. Traditional bareground culture was compared with several colored mulches (white, silver, red, black, and blue) for their effects on head formation, size, yield, and color of two Italian cultivars. Field studies were conducted in Freeville (upstate), N.Y., in 1997 and 1998. The percentage of heads harvested ranged from 32% to 82% over the 2 years of experiments and was lowest in black and red plastic mulch treatments. Yields were significantly higher, heads larger, and harvest earlier for plants grown over silver and white mulch compared to the control and other mulch treatments in 1998. In addition, average head weight was greater in all mulch treatments except blue when compared with the control. Cultivar differences were measured for the number and weight of heads, the percent bolting and marketable heads, and head color in 1998. Air and soil temperatures varied significantly around these mulches; however, these differences in microclimate had no effect on head color quality. Despite relatively moderate temperatures in upstate New York, radicchio responded positively to mulches that lowered average soil temperatures (white and silver) compared with the other treatments.