NUTRIENT SOLUTION CONCENTRATION AFFECTS GROWTH OF SUBIRRIGATED BEDDING PLANTS

Abstract

To evaluate the effects of nutrient solution concentration on growth of alyssum [Lobularia maritima (L.) Desv. ‘New Carpet of Snow’], celosia (Celosia argentea L. ‘Gloria Scarlet’), dianthus (Dianthus chinensis L. ‘Telstar Crimson’), gomphrena (Gomphrena globosa L. ‘Gnome White’), stock [Matthiola incana (L.) R. Br ‘Special Mix’], and zinnia (Zinnia elegans Jacq. ‘Dreamland Mix’), we grew plants with five different concentrations of Hoagland nutrient solution [0.125, 0.25, 0.5, 1.0, and 2.0×full strength; electrical conductivity (EC) of 0.4, 0.7, 1.1, 2.0, and 3.7 dS m−1, respectively]. Plant growth of alyssum was maximized when plants were fertilized with 1.0×concentration of Hoagland solution, resulting in a final growing medium EC of 2.1 dS m−1 (as determined by the pour-through method). Maximum shoot dry mass of celosia was obtained when plants were fertilized with 0.5 to 1.0×concentration of Hoagland solution, resulting in a growing medium EC of 1.1–2.5 dS m−1. Growth of dianthus was best with a 1.0×concentration, resulting in a growing medium EC of approximately 3.7 dS m−1. However, dianthus had the most flowers when fertilized with a 2.0×solution. The concentration of nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), boron (B), and iron (Fe) in the shoots of dianthus increased, while the concentrations of molybdenum (Mo) and zinc (Zn) decreased with increasing fertilizer concentration. Gomphrena and stock preferred high fertilizer concentrations (1.0 to 2.0×), which resulted in maximum dry mass of both species, and the most flowers on gomphrena. The growing medium EC associated with the best growth of gomphrena and stock was relatively high (2.3–6.5 dS m−1). This suggests that both gomphrena and stock can tolerate relatively high levels of root zone salinity. Dry mass of zinnia was maximal with a 0.5×fertilizer concentration and a growing medium EC of 1.0 dS m−1. Flower diameter of zinnia decreased with increasing nutrient concentrations. In general, the growing medium pH was similar with low concentrations (0.125, 0.25, and 0.5×), but decreased with a further increase in fertilizer concentration.