Abstract
The North American market for herbal medicine has been rapidly growing over the past 20 yr. This has effectively created a stro ng public and regulatory demand for high quality, uniformity and safety of medicinal plant products. Greenhouse hydroponic cultivation under controlled environmental conditions allows the grower to provide pesticide-free conditions, lacking environmental contaminants, resulting in superior product quality and consistency. Calendula officinalis is evaluated here as an alternative greenhouse crop. Growing conditions (P concentrations) were manipulated in order to maximize flower-head (capitulum) yield, as the se are the most valuable marketable structures. It was found that high P concentrations did not increase flower production, but instead produced significantly more leaf biomass.Plants receiving the lowest P concentration, with an intermittent watering reg ime, had the greatest absolute reproductive output, and greatest mass of all tissues assessed, except for leaf tissue. They also had the greatest proportion of biomass allocated to reproductive structures. Calendula officinalis shows promise as a medicinal greenhouse crop that requires low P levels for optimal capitulum (inflorescence) production (target tissue). Its xerophytic characteristics are best supported through modification of standard hydroponic systems; these modifications may be widely applicab le to medicinal plants since many share Calendula’s xerophytic characteristics. We conclude that discontinuous nutrient supply and relatively low ratios of P relative to N and K may enhance production of target medicinal tissues of Calendula officinalis. Key words:
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