This week horticulture staff are begining to remove all the leaves from next spring's hydrangea crop. You may be wondering why we would remove all the leaves from perfectly healthy plants. Hydrangea plants need to undergo a dormancy in order to flower. Outside, they would go dormant in the winter when temperatures drop. In the greenhouse we have to fake that seasonal change. When they go into dormancy, hydrangeas lose most of their leaves, so taking them off ahead of time reduces the mess later. Not doing so could result in old, dead leaves accumulating and harboring disease.
Hydrangeas are a major feature of the Conservatory's Spring Flower Show and require nearly 10 months of care before they go on display. The conservatory starts all of our hydrangeas from unrooted cuttings we receive in the middle of June. We grow them up through the summer and let them set buds before providing the dormancy the will need to flower. The hydrangeas will be dormant in a cold area of the greenhouse for approximately eight weeks. Then they are moved to a warmer spot where they can begin actively growing again and flowering. Horticulture staff use specially timed "feedings" of ammonium sulfate to ensure the development of blue flowers. This year we are growing mostly a variety called 'Oregon Pride.' This is a variety we have used successfully in past years. We are also experimenting with eight new varieties to see if they perform as well (or better!) than our traditional selections. Look for these hydrangeas in the Sunken Garden next spring.