Plant growth regulators cannot be used to alter significantly the commercial harvest date of Boronia heterophylla F. Muell. (Rutaceae)

Harvest of the cut flower crop, Boronia heterophylla F. Muell., is restricted to a 2-week period in early spring. Extension of the flowering period by plant growth regulators was examined in plants growing in the field under standard, commercial production conditions. Flowering time, and hence harvest date, were delayed by 6-9 days following the application of gibberellic acid and benzyl adenine (GA(4+7)+BA). High concentrations of GA(4+7)+BA (40, 80 mg/L) delayed flowering longer than 20 mg/L, but reduced flower number. BA alone (4 applications of 20, 50, or 100 mg/L) reduced flower number and did not affect harvest date. GA(3) (4 applications of 20 mg/L) prevented flowering. Paclobutrazol (100 mg/L) reduced flower number and delayed flowering by 4 days. The timing of applications at the commencement of flower-promoting conditions, when plants had been exposed to 10-20 nights of temperatures