Effects of air humidity and K/Ca ratio in the nutrient supply on growth and postharvest characteristics of cut roses

Single node cuttings with one mature leaf were taken from the rose cv. Baroness and rooted in water culture. The rooted plants were grown in nutrient solutions and subjected to two levels of relative air humidity (RH): high (90%) and moderate (70%), in combination with high (12/1), medium (1/1) and low (115) K/Ca ratios in the nutrient solution. High RH plants accumulated less Ca in leaves and flowers than moderate RH plants. Roses grown at moderate RH had a longer postharvest life than high RH roses, irrespective of the K/Ca ratio of the nutrient solution. In general, a high K/Ca ratio had a negative impact on postharvest life. When grown at a high K/Ca ratio the ornamental value declined rapidly, mainly due to the appearance of necrotic petals as well as chlorotic and necrotic areas on the leaves. Bent neck occurred only with high RH plants but changes in the K/Ca ratio had no differential effect. Dry spots and brittle leaves were observed on high RH roses, and the occurrence increased with increased K/Ca ratio in the nutrient solution. Stomatal conductance increased in parallel with increases in RH and K/Ca ratio when measured on intact roses placed in dry air (40% RH). (C) 2001 Elsevier Science B.V. All rights reserved.