Selecting and caring for hydrangeas
We're heading into high season for hydrangeas, one of the showier shrubs in the landscape. With their moptop and lacecap flowers, these plants perform year-round as their flowers dry to autumn hues, then winter whites.
There are two basic types of hydrangeas (Hydrangea), those that bloom on year-old growth and those that bloom on current season growth.
The big leaf hydrangea (H. macrophylla) forms flower buds in late summer and fall. In the upper Midwest and other cold climates, freezing temperatures in late spring frequently zap these buds, causing the plant to grow leaves, but no blooms.
You can reduce this threat by siting a big leaf hydrangea where it's buffered from drying winds and freezing temperatures. Many Northern gardeners protect the plant by making a sleeve to fit around it and filling the sleeve with leaves in fall.
The leaf-stuffed sleeve stays on until spring, when there's no danger of a hard freeze. The sleeve can be made of cloth, such as burlap, or it can be a plastic trash can with the bottom cut out.
The big leaf hydrangea is better suited for the more moderate climates in the West, South and Southeast. If you need to prune big leaf hydrangeas, or the native oakleaf hydrangea (H. quercifolia), do so within a month after it blooms.
Although the oakleaf blooms on year-old growth, it does so later in the season so its flower buds are less likely to be damaged by late spring temperatures, making it more reliable in Northern gardens.
Breeders have begun marketing big leaf hydrangeas that bloom on new and old growth. Endless Summer is probably the best known.
The color of the flowers on big leaf hydrangeas depends on the soil. Acidic soil produces flowers in the blue range and hydrangeas planted in alkaline soil have blooms in the pink palette. You can add alumninum sulphate to hydrangeas planted in alkaline soil to turn them blue and lime to those planted in acidic soil to turn them pink.
The most reliable selections for cold climates are the smooth-leaf hydrangea (H. arborescens), such as the moptop "Annabelle," lacecap "White Dome," and cone-shaped H. paniculata, commonly referred to as peegee hydrangea.
All of these hydrangeas bloom on current season growth, which means you can prune them in spring without cutting off summer's flowers. The colors on these hydrangeas cannot be altered.
Plant hydrangeas in shade to part sun. They tolerate full sun, but will need supplemental watering. All hydrangeas do best in soil rich in organic matter. The native smooth-leaf hydrangea can handle fairly wet soil to dry.
Apply an inch of compost to the soil around hydrangeas in spring as they start to develop their leaves. If using a soil additive or hydrangea fertilizer, always read and follow the label directions.
Sometimes known as the Hoosier Gardener, Jo Ellen Meyers Sharp lives in Indianapolis and is part owner and editor of Indiana Living Green magazine. Her work has also appeared in many other publications, including The American Gardener, Garden Gate and Greenhouse Grower. In addition, Meyers Sharp speaks about gardening and sustainable living throughout the Midwest and is a director of the Garden Writers Association.