Growth and flower initiation in hydrangea as affected by root restriction and defoliation

Abstract

Effects of container volume and leaf removal on growth and flowering were studied in Hydrangea macrophylla Thunb. ‘Leuchtfeuer’ under conditions conducive to flower initiation. After greenhouse (18°C) conditions for 82 days, container volumes of 140 and 150 cm 3 reduced shoot and root dry weights, numbers of expanded leaves and flower initiation, but increased shoot:root ratio when compared with the plants in 260 and 320 cm 3 pots. After phytotron (14°C) conditions for 50 days, removal of six leaf pairs prevented flower initiation while no defoliation resulted in 100% of plants with flowers initiated. Removal of the upper three expanded leaf pairs increased basal bud size and resulted in 10% of plants with flowers initiated, while removal of the lower three expanded leaf pairs promoted apical bud growth and resulted in 89% of plants with flowers initiated. Reduced flower initiation was associated with both root restriction and defoliation treatments where the dry matter partitioning was changed and numbers of the upper expanded leaves were reduced.