Observations on environmental control of flowering of Qualup bell (Pimelea phyodes)

The attractive Western Australian native cut flower, Pimelea physodes (Qualup bell), was grown in a cooler climate at Mt Barker and a warmer climate at Medina. Buds appeared much earlier (7 weeks) at Mt Barker and flower opening was earlier but the time between these events was greater (i.e. the duration of flower development was 1.7 times longer) at Mt Barker compared with Medina. Temperatures at Mt Barker were lower than at Medina, but at both latitudes the temperature averaged over the 2 weeks up to when buds appeared was similar (i.e. about 20/10°C day/night). During bud appearance daylength was 10 h or less at both sites. Plants at Mt Barker produced fewer flowering stems but more stems per plant compared with Medina. Since there were more stems and a longer development period for the plants at Mt Barker, the total number of flowers per plant was 3.7 times higher than those at the Medina site. Longer flower development did not affect flower size at Mt Barker with flower size remaining the same at both latitudes. Flower opening occurred at a similar rate at both latitudes and could be described by a linear function with about 3% change in opening per day.Bud appearance and flowering was promoted by a short-term pulse of cooling (10/15°C day/night) followed by warmer conditions (day/night temperature range; 20/11°C to 17/7°C over 5 weeks), with a longer cool pulse giving earlier bud appearance but not affecting flower appearance. Under cold pulse treatment flowers opened more rapidly giving a fuller flower display. A 2-week cold pulse resulted in an increase in flower production while a longer 4-week pulse reduced flower production. The impact on floral display is discussed. Results from trials indicated that by choosing sites with different temperature conditions such as at different latitudes or altitudes or subjecting plants to a cold pulse it should be possible to spread the flowering time of P. physodes.