Change in the unseasonal flowering occurrence on hydrangea basal shoots under forcing condition

With the aim of obtaining fundamental information on the flowering of apical buds on hydrangea (Hydrangea spp.) basal shoots, the flowering rate and flowering period duration of basal shoots were studied. Flowering was observed in 14.1% of basal shoots of ‘Glowing Alps’ occurring from July to November 2013 and in 72.2% of basal shoots of ‘Magical Diamond’ occurring from June to November 2013. In both cultivars, previously formed shoots flowered from June to July 2013, and the flowering rates were 97.2% and 93.3% in ‘Glowing Alps’ and ‘Magical Diamond’, respectively. The effectiveness of forcing on the flowering of hydrangea basal shoots was also studied. The cultivation area was maintained above 5°C from early winter, and flowering of apical buds from basal shoots was studied. ‘Glowing Alps’ and ‘Magical Diamond’ developed flowers on 43.4% and 75.0% of studied basal shoots before November 2013, indicating that forcing successfully increased the flowering of basal shoots in ‘Glowing Alps’. In conclusion, flowering rate of basal shoots was lower but the flowering period was longer than the corresponding traits of previously formed shoots. Forcing increased the flowering rate of basal shoots in the hydrangea cultivars with lower unseasonal flowering potential.