Effects of CaCl2 solutions to alleviate drought stress effects in potted ornamentals Salvia splendens and Ageratum houstonianum

Bedding plants are often subjected to soil water deficit – either after planting and/or during the market chain. Methods to alleviate the negative water stress effects are sought for to preserve ornamental values of plants. The aim of this study was to evaluate the response of two bedding plants, Ageratum houstonianum Mill. and Salvia splendens Sellow ex Scult., to water stress and treatments with calcium chloride aimed to alleviate drought effects. Plants were subjected either to 45 days of periodical stress (five cycles when watering was off for 5 consecutive days, followed by four cycles on for 5 consecutive days) or 10 days of radical drought (complete water withdrawal). On the first day, before the onset of drought, plants were watered with 0.5% Ca or 1% Ca w/v as a solution of calcium chloride (5 g or 10 g Ca per 1 dm3 of the growing substrate). The similarly Ca-treated but routinely watered plants provided controls to evaluate the water shortage effects. Plant height, inflorescence length/number, leaf number, leaf area (in Salvia splendens only), aboveground plant part weight, and root weight (in Salvia splendens only) as well as leaf relative water content (RWC) were measured at the beginning and at the end of the experiments. Water withdrawal during 10 days of growth (radical drought) reduced by half RWC in leaves of withering Salvia splendens and Ageratum houstonianum plants. Its effects on the growth parameters were less pronounced and mitigated by Ca applications. Also in the periodically stressed plants of both species, RWC and most growth parameters were reduced by water shortage but Ca applications alleviated the negative stress effects