EFFECT OF ROOT-ZONE AND AIR-TEMPERATURE ON FLOWERING, GROWTH AND KEEPING QUALITY OF BEGONIA X HIEMALIS TORAN

Begonia × hiemalis 'Toran' was subjected to different root-zone temperatures up to 29°C on heated aluminium benches combined with a general greenhouse air temperature of 19-20°C or less. The aluminium bench increased the temperature among the plants to 5°C above the air temperature during the night, depending on the root-zone temperature setting, growing season and greenhouse air temperature. Narrow air temperature tolerances were found for flowering, with an optimal value of 18-19°C in the winter season, whereas the root-zone temperature was of less importance in the range between 18 and 26°C. Lowering the root-zone temperature during the generative stage of growth did not improve the flowering response, compared with a continuous high root-zone temperature of 29°C. Root-zone and air temperatures were more critical for flowering than for growth rate or specific leaf area in the temperature range investigated. The post-harvest experiments demonstrated similar tolerances for air and root-zone temperature. Flowering was severly affected by a long period of drought in darkness during transport simulation, but not if light was supplied during this simulation. © 1990.