FLOWERING ADVANCEMENT IN HERBACEOUS PEONY

Abstract

Cut peony flowers are highly valued in the market, but they are available only for a short period in the late spring and early summer. Peonies have been reported to flower successfully in areas with 2-3 months of freezing temperatures. Our earlier studies revealed, however, that they can bloom successfully in warmer areas with prevailing temperatures above freezing. This was the basis for developing peonies as a cut flower crop in the higher elevation, cooler regions of Israel. The aim of the project was to evaluate the growth cycle of peonies in Israel and to study the effect of environmental conditions on flower formation and dormancy. Periodical morphological studies revealed that flower bud initiation in the underground renewal buds began in late summer and continued until the plants shed their leaves and became dormant in November. Both flower formation and dormancy are autonomous and do not depend on photoperiod. The release from dormancy requires the accumulation of a certain number of chill units, which varies between cultivars. Moderate temperatures are required both during the summer when new flower buds are initiated and following dormancy breaking when the flowers grow and develop. Higher growing temperatures promote flower bud abortion. Based on this information, two methods were developed for flowering advancement: 1. Growing plants in containers, exposing them to 1-3°C for 6 to 10 weeks in late autumn, drenching the soil with GA3, and moving the containerized plants to unheated greenhouses for growing and blooming. With this method a very early crop can be obtained from mid-January on. 2. Field-grown plants in uncovered greenhouses are exposed to natural winter cold temperatures until they receive a certain number of predetermined chill units. They are then drenched with GA3 and the greenhouses are covered with plastic sheets. Such plants flower about one month earlier than untreated plants grown in open fields.