ISHS Acta Horticulturae 548: International Symposium on Growing Media and Hydroponics
GROWTH CONTROL OF HYDRANGEA MACROPHYLLA THROUGH WATER RESTRICTION |
| Author: | P. Morel |
| Keywords: | irrigation, potted plant, quality |
| Abstract:
Hydrangea macrophylla is a semi-hardwood bushy plant much used in Europe as an indoor potted plant. Its growth schedule is carried out in two steps: an initial growing period outside, from May to October forms the plant architecture, followed by a second phase in the greenhouse, the following year, to obtain early flowering (from March to May). Through all growing periods, plant growth must be controlled to obtain compact plants. Thus, while growth regulators are commonly used, economical and ecological reasons may limit their usefulness. Consequently, new crop management strategies must be designed. Water restriction during phases of shoot elongation can be one of these strategies. A trial was conducted on plants cultivated on a white peat:composted bark (10-15 mm), 2:3 mix. They were watered by drip irrigation during the outdoor growth (Ph1) and by subirrigation during forcing in the greenhouse (Ph2). At each stage, two levels of water potential were applied: a high level, corresponding to 'water comfort' (WC), -5kPa in Ph1, -8kPa in Ph2, and a low level, corresponding to 'water restriction' (WR), -16kPa in Ph1 and -20kPa in Ph2. During phase 2, both treatments were combined to obtain the following four treatments: WC/WC, WC/WR, WR/WC and WR/WC. Water potential was monitored continuously and irrigation scheduled using tensiometers linked to an automatic control device. After 11 weeks under water restriction conditions during Ph1, growth reduction reached 64% for the amount of dry aerial biomass, 29% for leaf number and 40% for plant height. After 9 weeks under water restriction conditions during Ph2, leaf area and plant height were reduced respectively by 47% and 11% for WC/WR plants and by 52% and 37% for WR/WR plants. Inflorescence size was reduced with WR applied during Ph2 and number of flowers per inflorescence was reduced with WR applied during Ph1, but the attractive and commercial aspect of plants was much better with a water restriction during Ph1, then Ph2 (compactness, harmony between leaves and inflorescences). | |
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