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Cindy Haynes, Horticulture Extension, (515) 294- 4006,
Elaine Edwards, Extension Communication Systems, (515) 249-5168,

Yard and Garden Column for the Week Beginning June 30

Heavenly Hydrangeas

By Cindy Haynes
Extension horticulturist
Iowa State University Extension

Iowa gardens feature many wonderful spring-flowering shrubs. Yet, there are relatively few summer-blooming shrubs. One of the best and often overlooked groups of shrubs for summer bloom is the hydrangea. Several different species brighten the landscape with blooms during the summer months.

One of the most durable and reliable of the hydrangeas is smooth hydrangea (Hydrangea aborescens). This 3- to 5-foot shrub flowers freely from June to September. The flowers are rounded and change from an apple green to creamy white during the summer. Flowers also are showy in the fall as they fade to tan and persist into the winter. 'Annabelle' is one of the most popular cultivars and is noted for its large (almost one-foot diameter) flower heads. This variety can be spotted from great distance. The flowers are often so heavy they weigh the stems to the ground giving the shrub a "weeping effect." For plenty of flowers and dense dark green leaves, plant smooth hydrangea in full sun to partial shade. Smooth hydrangea is tolerant of many soil types but prefers moist, well-drained soils. This is one of the hardiest of the hydrangeas often surviving into USDA hardiness zone 3 or northern Minnesota.

The panicle hydrangea (Hydrangea paniculata) blooms later than the smooth hydrangea, often not starting until July. But the 6- to 12-inch-long, cone-shaped, creamy white flowers are equally persistent. As the flowers age, they often become a mottled pink. This is the largest of the shrub-type hydrangeas often reaching 10 feet or more in height. There are many wonderful cultivars in this species with 'Grandiflora,' or PeeGee, being one of the most popular. Once again the flowers are so large they often weigh down the branches. Panicle hydrangea is a vigorous grower that is hardy to USDA hardiness zone 3 and a reliable bloomer in the Iowa landscape. It is often fashioned into small trees to make attractive specimens in the garden.

One of the most interesting hydrangea species is the Oakleaf hydrangea (Hydrangea quercifolia). The coarse leaves are 3 to 8 inches long and shaped like oak leaves, hence the common name. The foliage also is noted for its attractive, red-burgundy fall color. This three- to five-foot shrub has showy cone-shaped, creamy white flowers in June and July. Like panicle hydrangea, the flowers often develop pinkish undertones as they mature. The oakleaf hydrangea is considered hardy to USDA hardiness zone 5. It should perform well in protected sites in southern Iowa, but may not survive in northern areas of the state. It prefers partial shade in fertile, moist, well-drained soil with protection from harsh winter winds. Several cultivars are available. These cultivars vary in plant height from 2 to 12 feet. Flower heads can be 4 to 14 inches long depending on cultivar.

Not all hydrangeas are shrubs. One such example is climbing hydrangea (Hydrangea anomala ssp. petiolaris). Many notable horticulturists have praised climbing hydrangea as the best landscape vine. It clings easily to tree bark or other structures and is almost unlimited in its ability to climb, often reaching more than 50 feet in height. The white flowers appear in 6- to 10-inch diameter, flat-topped corymbs in early July and persist for several weeks. The glossy, dark green leaves provide the perfect backdrop to show off the blossoms. Another interesting feature of this plant is its exfoliating brown bark. The shaggy bark adds a great deal of interest in the winter making this a multi-season ornamental plant. As with most hydrangeas, climbing hydrangea prefers partial shade to full sun with a moist, fertile, well-drained soil. Plants are often slow to establish, taking a couple of years before vigorous growth begins. Support also will be needed as the plants become established and to direct growth. Give this one plenty of room and watch it grow.

Bigleaf hydrangea (Hydrangea macrophylla) is the attention-grabbing blue or pink hydrangea in florist shops and supermarkets. While this is an excellent, long-blooming, 3- to 5-foot shrub in my home state of Louisiana, it does not tolerate Iowa winters as well as I do. Bigleaf hydrangeas bloom on the previous season's growth. Unfortunately in Iowa they often die back to the ground in the winter. As a result, they seldom bloom. Even placement in a protected site with fertile, moist, well-drained soil will not guarantee blooms every year. Fortunately the glossy, spring-green foliage makes a nice compliment to summer blooming perennials.

Another added bonus to most hydrangea flowers is that they make excellent cut and dried flowers. You can bring the blossoms inside to brighten the indoor landscape. Let hydrangeas cool your landscape with their cheery blossoms all summer.


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