Hydrangeas grace the landscape with beautiful flowers in the spring and summer. They are considered heritage plants as they are often handed down from generation to generation. They may seem old fashioned, but the multiple varieties available provide gardeners with something new.
The most colorful hydrangeas are bigleaf hydrangeas, Hydrangea macrophylla. Their flowers are usually either pink or blue. Flower color depends on the pH of the soil, a measure of soil acidity. Soil pH can be raised by applying lime. Some hydrangeas will respond to a higher pH (between 6.0 and 6.5) with pink flower color. To lower pH, apply aluminum sulfate. A lower pH (between 5.0 and 5.5) often results in blue flower color. A soil test will determine the existing pH and you can change your soil with the appropriate amendment to get the resulting flower color you want.
Hydrangeas grow best in moist, well-drained soil and partial shade. When planted in full sun in our summer heat, they have a tendency to wilt. The north side of a house or a location where the plant receives afternoon shade is best.
There are two flower forms of bigleaf hydrangea -- mophead and lacecap. Mophead types make a full, large, round ball of sepals. The showy parts of the flower are the sepals, which surround the flower bud. The lacecap type has flower buds surrounded by showy sepals along the outside edge of the flower head. The inside of the flower head has buds but lacks the showy sepals. The type of flower head a plant produces depends on the cultivar.
Most bigleaf hydrangeas bloom on previous season's growth. Part of last year's growth may be injured by cold weather during winter. As buds begin to show green in the spring, you will be able to determine how much wood is still living. The dead wood should be pruned out. Stems can be pruned lower as long as there are still some live buds below the pruning cut. Flower buds are more sensitive to cold temperatures than leaf buds. Until your plant begins to flower, it will be hard to know if all the flower buds are living.
New cultivars called re-blooming hydrangeas have been released with the advantage of blooming on old wood and new growth. Endless Summer (released in 1998) is a true re-blooming hydrangea. It has a mophead flower type up to 8 inches in diameter with pink or blue color, depending on pH. The plant is 3 to 4 feet tall.
The "Let's Dance Moonlight" Hydrangea, released as part of the Proven Winner's Top 10 Flowering Shrubs of 2013 series, is another repeat bloomer that delivers a long season of exceptional flower color. The large blooms can be pink or blue depending on soil pH.
A new cultivar named "Pistachio" from Ball Horticultural gives a color spin to the blue and pink decision. This reblooming hydrangea holds 5-inch-wide mops of scarlet blossoms with a blue center and edged with bright green. Very unusual.
Kelly R. Jackson is the Christian County Extension Agent for horticulture. He can be reached at 270-886-6328 or visit Christian County Horticulture online at www.christiancountyextension.com.