Optimum Feeding Nutrient Solution Concentration for Greenhouse Potted Miniature Rose Production in a Recirculating Subirrigation System

To determine the optimum feeding nutrient solution concentrations for the production of potted miniature roses (Rosa chineersis minima 'Fall Festival') under recirculating subirrigation conditions, plants were grown under four different nutrient solution concentrations [25%, 50%, 75%, and 100% of the full strength with an electrical conductivity (EC) of 1.756 dS.m(-1)]. Nutrient solution concentrations affected the stem, root, and plant total dry weight and flower and branch number. Under the 75% strength nutrient solution, these growth parameters were equal to or better than the 100% strength solution. No difference was detected in the chlorophyll content of leaves from plants that received the 50%, 75%, and 100% strength solutions during the experiment but at Day 35; only the 25% treatment had significantly lower leaf chlorophyll content than the other treatments. There were no treatment effects on the measured total foliar nutrient contents [except potassium (K)] of plants under the 75% strength solution compared with those under the 100% treatment, but nitrogen (N), phosphorus (P), and/or iron (Fe) of plants under the 25% strength solutions were below that of the acceptable range. Interveinal chlorosis and/or reddish leaves and branches were also apparent in plants under the 25% and 50% strength solutions. It is suspected that these are symptoms of N, P, and Fe deficiencies caused by the reduced nutrient solution concentrations and increased pH of the growing substrate. There were significant depletions of N and P nutrients in the 25% and 50% strength solutions at the end of the experiment, which was consistent with visual symptoms and deficiencies. Nutrient salts accumulated in the top section of the growing substrate under all treatments, but no phytotoxic effects were observed. The EC values for the top third of the growing substrate were much higher than those of the bottom two-thirds. EC for the top layer of the 100% treatment exhibited a fourfold increase compared with the bottom layer of that treatment. The NO3-, K, magnesium, and calcium for the top layer of the 100% treatment were 235%, 149%, 287%, and 245%, respectively, higher compared with the bottom layer of the 100% treatment. It was concluded that the nutrient solution concentrations typically used for potted miniature rose production in most of the Canadian greenhouses under recirculating subirrigation conditions can be safely reduced to 75% and produce better plants.