Pinching, Daminozide and Night-interrupted Lighting Start Date Affect Growth and Flowering of Achillea × ‘Coronation Gold’

Abstract

A study was conducted to determine the effects of pinching and the plant growth retardant, daminozide (B-Nine), on plant size and flowering of ‘Coronation Gold’ yarrow (Achillea × ‘Coronation Gold’). Greenhouse-grown plants were not pinched or were pinched by removing the apical bud from propagation offsets 3, 5 or 7 weeks after potting. One week after pinching, plants were provided night-interrupted lighting (NIL). Five weeks after pinching, a single application of daminozide was applied at 5,000 ppm to half the pinched and non-pinched plants. Pinching decreased inflorescence stem length by 6.4% and increased the number of flowering and total offsets by 33.3 and 9.1%, respectively. Daminozide application decreased inflorescence stem length and the number of flowering offsets by 7.9 and 40%, respectively, but increased the time to first open inflorescence and the number of non-flowering offsets by 6 days and 28.6%, respectively. Pinching at 7 weeks after potting resulted in the highest number of flowering, non-flowering, and total offsets, the fewest days to flower, and an intermediate flower stem length. In a second experiment, the effects of beginning NIL at different times after pinching the offset from propagation on offset production and flowering were evaluated. All plants were uniformly pinched and NIL was started 0, 1, 2, 3, or 4 weeks after pinching. Starting NIL at 4 weeks after pinching resulted in the fewest days to flower, the highest flowering offset number that was similar to starting NIL at 3 weeks, and a flower stem length about equal to all other NIL treatments.