Potassium Application to Chrysanthemums Grown Hydroponically for the Cut Flower Production

The relationship between growth of chrysanthemum cv. Seiun and their potassium (K) up-take capacity from hydroponic solutions of various K concentrations was investigated. From the results the optimum K application level for cut flower production was derived.1. In Experiment 1, the growth rates of plants grown at 30, 75, 150 and 300 ppm K were similar up to the flower budding stage. At 30, 75 and 150 ppm K, the chrysanthemum plants absorbed the same amount of K; at 300 ppm K, plants absorbed 1.2 times more K.2. In Experiment 2, which began on 3 May and ended on 28 June, there were six plots: one was adjusted weekly to 150 ppm K; the other five plots were supplied 2, 000, 1, 500, 1, 000, 500 and 100 mg K per plant at the beginning of the experiment. Plants supplied 2, 000, 1, 500 and 1, 000 mg K produced the good quality cut flowers; those supplied 500 mg K had small upper leaves, whereas middle and lower leaves of plants given 100 mg K exhibited necrosis and/or chlorosis, typical K deficiency symptoms. Plants grown at a constant 150 ppm K level had excessively large leaves and short flower stalks.3. Potassium contents in leaves and roots increased with increasing K concentration in the culture solution. Even when 2, 000 mg per plant were absorbed, excess K symptom was not observed. When leaf K content decreased below 4.0% on a dry matter basis, leaf Ca and Mg contents increased inversely.Based on our results, we recommend that 25 to 30 kg of potassium fertilizer (as K2O) is applied to produce 40, 000 cut chrysanthemum flowers per 1, 000m2 of green house space.