Growth and Yield of Six Medicinal Herbs in Response to Mulch Type

Abstract

Weeds are a major concern in the production of many medicinal herbs. Weeds can interfere with the growth of the herb, reducing yields of foliage, flowers, and roots. The presence of weeds in the harvested herb can lessen the value of the herb or render it unmarketable. Weed control on medicinal herbs is difficult because there are few herbicides cleared for use and many herbs are organically grown. In this study, we examined the use of white and black plastic mulches to control weeds in the production of six medicinal herbs in the northern piedmont region of North Carolina. The herbs were grown for 2 years on raised beds with drip-irrigation. The beds were left bare or covered with black plastic mulch or white plastic mulch. The herbs grown were Arnica chamissonis, Echinacea angustifolia, Echinacea purpurea, Leonurus cardiaca, Scutellaria lateriflora, and Spilanthes oleracea. Transplants were field set in May and June. Depending on the particular herb, foliage, and flowers were harvested during both growing seasons and roots were harvested at the end of the second season. Both plastic mulches provided excellent weed control compared to the bare ground treatment. A. chamissonis flower yields were reduced when plants were grown with either plastic mulch. Growth and yield of E. angustifolia, L. cardiaca, and S. lateriflora were unaffected by any mulch treatment. In contrast, total season yields of E. purpurea tops (stems, leaves, and flowers) and roots were higher with both plastic mulches than with the bare ground treatment. Root yields of S. oleracea were higher with the bare ground treatment than with either mulch, but top yields were unaffected by treatment.