Optimal Temperature for Hydrangeas

Optimal Temperatures

• The optimal temperature range for hydrangeas during the day is between 65 and 75 F. The best nighttime temperature range is between 55 to 60 F. Hydrangeas prefer warm temperatures during the growing season, but can survive cold temperatures when they have gone dormant. When hydrangeas have entered dormancy, they stop producing blooms and defoliate their leaves.

Zones

• Hydrangeas fit into different U.S. Department of Agriculture plant hardiness zones depending on the cultivar. These hardiness zones represent the average minimum temperature range for the area, and gardeners can tell whether a particular plant is likely to survive the winter in that climate. For example, oakleaf hydrangeas can live in USDA zones 5 through 9, and tolerate temperatures as low as minus 20 to 30 F. Hydrangea paniculata plants are hardy in zones 3 through 8, which get as cold as minus 40 through 30 F.

Damage from Cold Weather

• Hydrangeas that are exposed to temperatures below their tolerance level display winter injuries to the stem or other parts of the plant. Problems can occur when plants break dormancy in the late winter when temperatures rise and then dip back into freezing. The newly formed buds become injured. Winter injury may prevent the hydrangea from blooming during the growing season, even when temperatures are optimal.

  Gardeners can prevent this damage by moving hydrangea plants inside when they see blooms or before a freeze. Pick off dead leaves from your hydrangea and keep it in a room that receives nighttime temperatures between 55 to 60 F, suggests the University of Missouri. Place the hydrangea near a sunny window during the day. Move the plant back outside when temperatures rise in the spring.

Location

• Gardeners may be able to improve the temperature conditions for their hydrangeas by placing the plants in certain areas in the yard. Those living in regions that receive cool temperatures can plant hydrangeas in south-facing parts of the yard, where they will get extra sun throughout the day. Those living in regions that experience hot summer temperatures above 80 F can place plants in areas with partial shade to reduce the heat. If the plant experiences problems blooming in the shade, find a planting site with a little more light.