Florist’s hydrangeas are native to the temperate, maritime climate of Japan, on the Pacific side of Honshu Island. While crown hardy to USDA Zone 6, florist’s hydrangeas cannot be expected to flower in your area (Illinois) without protection.
Flowers are born on last year’s shoots, and these are often killed by cold winter temperatures. If it is cold outside, cut back the blooms and treat it as a houseplant until you can move it outside after the danger of frost in the spring.
These hydrangeas have become popular florist plants, forced into flower for holidays ranging from Valentine’s day to Memorial Day. The showy, sterile flowers that make up the rounded inflorescence may be white or various tints and intensities of pink or blue.
Hydrangea flower color depends on soil pH and the availability of aluminum ions. An acid pH (5.2-5.5), created by the addition of aluminum sulfate, results in a deep blue color. Pink to red cultivars need a pH above 6 and ample amounts of phosphorus, which competes with the aluminum ions.
For an extended floral display in your home, keep your potted hydrangea well watered in a cool room (less than 70˚F) and with ample bright, indirect light. However, a florist’s hydrangea in bloom cannot be expected to bloom again in that same year. Don’t expect much in the way of bloom on a young hydrangea planted outdoors for the first two to three years.
Image Attribution: Wiki Commons
This post was excerpted from the May/June 2002 issue of Horticulture Magazine.
Learn how to prepare the right pH soil with Horticulture Smart Gardening Techniques: Soil.
Use the Eco Watering Spout to keep your hydrangeas and other potted plants hydrated.
Discover new ways to care for your perennials with The Perennial Care Manual.