Kamenetski, R., Department of Ornamental Horticulture, Volcani Center, ARO, P.O.B. 6, Bet Dagan 50250, Israel
Barzilay, A., Department of Ornamental Horticulture, Volcani Center, ARO, P.O.B. 6, Bet Dagan 50250, Israel
Cohen, M., NRD, Northern RandD, P.O.B. 831, Kiryat Shmona 11016, Israel

In spite of their beauty and wide use as garden plants in temperate climate regions, herbaceous peonies are less common as cut flowers, primarily because of their short flowering season from late spring to early summer. Peonies have been reported to flower successfully in areas with 2-3 months of freezing temperatures. However, our studies revealed that they can bloom successfully in areas with cool temperatures, above freezing. In the north of Israel, some peonies flowered in April-May. It was realized that for successful commercial production, the peony has to be subjected to low temperatures during the winter and to moderate-warm temperatures in summer. The aim of the project was to evaluate the growth cycle of peonies in Israel and to study the effect of environmental conditions on flowering 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. Moderate temperatures are required following dormancy breaking when the flowers grow and develop. Higher growing temperatures cause flower abortion. The information gained from these studies has formed the basis for developing three practical methods for cut flower production of herbaceous peonies in Israel: (1) Plants are grown in containers whereby all necessary environmental conditions for optimal flower development can be provided. With this method a very early crop can be obtained from mid-January on; (2) Field-grown plants in uncovered greenhouses are exposed to ambient cold temperatures until they receive a certain number of predetermined chill units. They are then covered with plastic sheets, to raise the growing temperatures. Such plants flower about one month earlier than plants grown in an open field, in March-April; (3) Peonies are grown in open plots and in net-houses for cut flower production in April-May.