JULY
2002

 

 

 

By
B. Rosie Lerner
 
Purdue Extension
Consumer
Horticulturist

 

 

 

 

 

7-18-02

Hydrangea Popular, but Challenging

Try to have a discussion about hydrangea among your gardening friends, and you're likely to start a rather lively debate. What type to grow, when to prune, why doesn't it flower and how can I change the flower color from pink to blue are among the most frequently asked hydrangea questions.

There are many different species of hydrangea, not to mention cultivars of those species. So, these questions are a bit difficult to answer, unless you know which specific plant is being discussed. Most hydrangea do well in full sun or partial shade. However, they thrive best in cool, moist soil. So if your site is hot and dry, it would be best to aim toward afternoon shade.

The hardiest of the hydrangea species is Panicle Hydrangea, H. paniculata. Despite its hardiness, it is not the showiest of plants and thus not as popular as some of the others. Panicle Hydrangea is generally a large shrub with white flowers in midsummer, changing to a faint purplish-pink as they age.

Smooth hydrangea, H. arborescens, produces large clusters of blooms that start out pale greenish, changing to white and then drying to papery brown. The cultivar 'Annabelle' has been quite popular for its very showy blooms, but can become rather weak-wooded and unkempt with age. It is probably best to treat this plant more as an herbaceous perennial, since it flowers on new growth, so cut it back severely to about 4-6 inches in late winter.

My personal favorite species is the Oakleaf Hydrangea, H. quercifolia, for its outstanding dramatic foliage, as well as showy blooms (most years) and fall leaf color. It is generally a large, coarse shrub, though some compact cultivars are available. It does tend to colonize a bit, so it is best planted where its volunteers will be welcome. The flower buds may be killed in severe winters, but appears to be able to tolerate -25 F.

Climbing hydrangea, H. anomala petiolaris, is a striking climbing vine with fragrant flowers. Although it can be slow to get started, once established, it will grow profuse foliage that clings to any type of support.

This brings us to the Bigleaf Hydrangea, H. macrophylla, certainly the most popular hydrangea across the United States. This is the plant with huge flower clusters whose color can be pink or blue, depending on the soil pH (blue flowers in acidic soil, pink flowers in alkaline soil). Southern Indiana gardeners have had some luck with this plant, but unfortunately for most Indiana gardeners, this particular species does not flower reliably in our area. It normally blooms on previous year's growth, and, because it breaks dormancy very early, its flower buds are most often killed in USDA hardiness zone 5. The vegetative buds often survive, or new shoots sprout from the roots if killed back to the ground, forming a tidy little foliage plant, but alas, no blooms.

However, there may be hope on the horizon for Hoosiers who long for this plant. A new cultivar called 'Endless Summer' originates from a planting in Minnesota, which appears to bloom reliably and repeatedly on current season's growth. 'Endless Summer' is scheduled for release in spring 2004 by Bailey's Nurseries in Minnesota and should be worth the wait.

 

Writer: B. Rosie Lerner
Editor: Olivia Maddox