In the work reported here, a preliminary experiment showed that rooted cuttings of H. Endless Summer could produce flowers without having received any chilling.
Flowering was unaffected by day-length. In the main experiment, H. Endless Summer was grown with H. 'Merritt Supreme Pink' and H. 'Blue Danube' — both need a chilling treatment before they can flower.
All plants were either "pinched" or not at the start of treatment and were then grown in short-days or short-days plus a night-break for six weeks. This was followed by chilling at 4 degsC for 1,000 hours. After this, the plants were grown in a greenhouse at day/night temperatures of 21 degsC/16.5 degsC with lighting for 16 hours each day from high-pressure sodium lamps.
H. Endless Summer flowered much earlier than the two cultivars but had fewer flowers than H. 'Blue Danube' and its branches were too short, especially when it was not pinched. The lack of a chilling requirement means H. Endless Summer has great potential as a flowering pot plant, but more work is needed to produce plants of the highest quality.
Comparative Forcing of Hydrangea macrophylla 'Bailer' (sic) as a Florist's Hydrangea by Anderson, Weiland, Pharis, Gagne, Janiga and Rosenow (2009). Scientia Horticulturae 122 (2): 221-226. The contents of issues of Scientia Horticulturae and abstracts of papers are provided at www.elsevier.com/locate/scihorti.