Vernalization and Growing Degree-day Requirements of Thalictrum delavayi `Hewitt's Double'

Abstract

Vernalization and growing degree-day requirements of Thalictrum delavayi `Hewitt's Double' were determined to improve the production scheduling of this cut flower crop. Two-year-old crowns of T. delavayi `Hewitt's Double', lifted in the fall, were exposed to cold storage for 0, 3, 6, 9, 12, or 15 weeks at 8 ± 1°C. After storage, the containerized plants were grown at Massey Univ., Palmerston North (40°20.S) in a greenhouse heated at 15°C and vented at 20°C, under a natural photoperiod (11 h increasing to 13 h) plus a 4-h night interruption between 2200 and 0200 HR. As buds continued to develop during storage at 8°C, growing degree-days calculations were made over both storage and greenhouse forcing periods. All plants flowered, but T. delavayi `Hewitt's Double' nevertheless showed a quantitative vernalization requirement, being fully saturated after 6 weeks of cold storage at 8°C. With a base temperature of 0°C, time to flowering reduced from 3338 degree-days without vernalization to an average 2804 degree-days subsequent to the saturation of the vernalization response (6 to 15 weeks of vernalization). Flower yield averaged between three and five stems per plant, with stem lengths ranging between 140 and 200 cm. Differences in flower yield and quality among storage durations were minor and not commercially significant.