By Maggie Oster
When it comes to trees and shrubs in the garden, late summer can be somewhat monochromatic. But, for me, this is exactly when I want some flowers, so my garden is plentifully planted with crape myrtles, caryopteris, shrub roses, rose-of-Sharon, and, most especially, hydrangeas. Although hydrangeas have long been a garden favorite, the many new hybrids produced in recent years, most particularly “Endless Summer,” have given this group of plants a renaissance. There is now a wider than ever range of plants with varying sizes, shapes, bloom times, and flower forms and colors. Explore the many possibilities and plan on adding some to your garden.
Types of Hydrangeas
At its most basic, hydrangeas can be divided into four types: big leaf (Hydrangea macrophylla), smooth (Hydrangea arborescens), panicle (Hydrangea paniculata), and oak leaf (Hydrangea quercifolia).
Big leaf hydrangeas are the ones with the big, round “snowballs” of flowers in pink or blue. This is the group to which Endless Summer belongs. Besides the snowball, or mophead, types, there are also ones called “lace caps,” which have a ring of showy sepals surrounding tiny fertile flowers. Most big leaf hydrangeas grow to 6 feet or so tall. Big leaf hydrangeas naturally bloom on last season’s growth. In colder areas (Zone 5 and lower), this meant that the plants survived but died back to the ground each winter and, hence, never bloomed. Endless Summer’ and the cultivars that have followed changed all that, as they bloom on both old and new wood.
The flower color of big leaf hydrangeas is dependent on the pH of the soil, with blue flowers in acid soil and pink ones in alkaline soil. To make soil more acid, use one-quarter ounce of aluminum sulfate per gallon of water. Apply at weekly intervals in the spring and fall. To make the soil more alkaline, apply one pound of lime to every ten square feet of soil area once or twice a year.
Smooth hydrangeas are native to the eastern half of the United States and hardy to Zone 3. They bloom on new wood with white flowers and grow 3 to 5 feet tall. In the wild, the flowers are not very showy, but the most widely available cultivar, ‘Annabelle’, has large white “snowballs” that age to green and brown. New varieties of the smooth hydrangea are now available, including a pink form, ‘Invincible Spirit’.
The oak leaf hydrangea is another eastern North America native, hardy to Zone 5, and growing to 6 feet or more tall and as wide. There are, however, dwarf forms that are ideal for smaller gardens. Large, pointed clusters of white flowers age to pink and wine-red. There are both single- and double-flowered forms. Besides the flowers, oak leaf hydrangeas are prized for their large, oak-shaped leaves, which turn a burgundy-red in the fall and the papery, peeling bark.
The best-known member of the panicle hydrangea family is “Grandiflora,” but there are other varieties. Whichever one you choose a panicle hydrangea is the star in late summer gardens. Growing to 15 feet or more tall, it may be seen as a shrub or small tree. The cone-shaped white flower clusters are 6 to 8 inches long, aging to a pinkish-purple. Hardy to Zone 3, this is the most adaptable of hydrangeas, surviving a wide range of soils.
Where and How to Plant Hydrangeas
Although there is some variation among the different types, generally, hydrangeas grow and bloom best where they get morning sun and afternoon shade. The further north one lives, the more sun that can be tolerated. Only panicle hydrangeas can tolerate all-day sun.
As to soil, most important is that it be well-drained. Whether its sandy or clay, work in some compost and use an organic mulch to improve the soil. Pot-grown plants can be planted any time, but early summer or fall is best. Plant at the same depth the hydrangea was planted in the pot. Keep the plant watered well until established.
Pruning Hydrangeas
To keep it simple, consider hydrangea pruning to come in two types. One is for big leaf and oak leaf hydrangeas, and the other is for smooth leaf and panicle hydrangeas.
For big leaf and oak leaf hydrangeas, which bloom on old wood, next year’s flower buds develop in August, September, and October, so pruning to shape or reduce size needs to be done earlier in the summer. Removing just the faded flowers or dead stems can be done at any time. The newer type of big leaf hydrangeas that bloom on both old and new wood can be pruned at any time.
For smooth leaf hydrangeas, I cut mine back to 6 inches every spring. The panicle hydrangeas can be trimmed as desired in fall, winter, or spring.
Hydrangeas are a wonderful group of plants, and I encourage you to add a wide range of them to your garden, starting right now.
