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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Hardy Hydrangeas

This article was published originally on 6/22/2001

Having problems with hydrangea shrubs flowering? Have you waited several years to see those knockout blue or pink ball-like blooms in your shady backyard?

The big leaf hydrangea (Hydrangea macrophylla) is the colorful shrub we see in florist shops and supermarkets and desire in our landscape. However, it is not reliably hardy in Iowa. Big leaf hydrangeas bloom on the previous season's growth. Since the stems often die back to the ground in the winter, they seldom bloom. Even placement in a protected site with fertile, moist, well-drained soil will not guarantee blooms every year.

But wait! Don't give up on hydrangeas yet. Hydrangeas are a wonderful group of summer blooming shrubs with several species that are hardy in Iowa.

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 are also 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 1-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. Other panicle hydrangea cultivars include 'Tardiva', 'Unique', 'Pink Diamond', 'White Moth', and 'Preacox'. These cultivars are also noted for their long cone-shaped blooms that turn varying shades of pink as they age.

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 is also noted for its attractive, red-burgundy fall color. This 3 to 5 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 on 'PeeWee' and up to 12 feet on 'Alice'. 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 over 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 will also be needed as the plants become established and to direct growth. Give this one plenty of room and watch it grow. Climbing hydrangea is hardy to USDA hardiness zone 4.

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.



This article originally appeared in the June 22, 2001 issue, pp. 78-79.

Year of Publication: 
2001
Issue: 
IC-485(15) -- June 22, 2001