Pennsylvania Flower Growers #182
Following the discovery by Stuart (5) that flow er buds were initiated on azaleas following treatment with growth retardants, studies were undertaken to determine how retardants might be used to induce flower buds on rhododendrons. Cathey (2) reported that liners of rhododendron 'Roseum Elegans' initiated flower buds three to five months after soil drenches of Phosfon or foliar sprays of Phosfon S or B-nine. More recently Cathey and Taylor (3) and Cathey (1) have released a summary of U.S.D.A. research with growth retardants on rhododendrons. Rooted rhododendron cuttings potted into five- or six-inch pots were pinched and pruned to three or four shoots. The effective retardant treatments were a Phosfon drench (0.2 g/5" pot) and B-nine spray (one quarter of one percent applied four times at monthly intervals). A night temperature of 65°F was maintained. A four-hour light interruption in the middle of the night with at least 20 f.c. of incandescent light was provided for 3-4 months or until flower buds were formed at which time the plants were given short day for 2-3 months. A two month cold storage at 50°F with 12 hours of light (lOf.c. minimum) was followed by forcing without supplemental light in a 65°F greenhouse. Whereas the untreated plants resumed vegetative growth, the treated plants came into flower 5-6 weeks after the start of forcing.
Keywords: Growth Retardants induce flower buds Phosfon B-nine Pinched and pruned Light interruption