Jan Maas: Master Garderner -- Not your grandmother’s hydrangeas
Hydrangeas have been part of the garden since the 1800s when "PeeGee" became a garden staple. "PeeGee" was tall with white flowers that had a floppy habit. It can still be found in gardens today. In recent years, there has been an explosion in hydrangea choices, including a variety of colors. These shrubs are a desirable addition to the garden and can be fairly easy to grow.
To choose the most desirable plant for your garden, you need to be aware of the different flower types. Actually, the "flowers" are clusters of flowers. The showy parts are the sterile flowers that attract pollinators to the less showy fertile flowers. The amount of each varies by cultivar. The flower clusters can be long and conical (panicles), large balls or flat and convex (lacecap). As with many plants, one size does not fit all so it’s important to understand the botanical name which can help to determine flower type, cold hardiness and optimal time pruning time. Hydrangeas prefer moist, well-drained but fertile soil in part shade to full sun.
There are four types of hydrangeas.
-- Hydrangea macrophylla, also known as lacecap or mophead, has the biggest number of the newest cultivars. They are also the least hardy, generally only to zone 5, and are known for changing color with soil acidity. Acid soils produce blue flowers and alkaline soils produce pink. They can be difficult to get to re-bloom in cold climates as they bloom on last year’s stems and can suffer winter injury. "Endless Summer" was a big hit when it first appeared on the scene a few years ago and is designated as hardy to zone 4. It does not bloom reliably in our area.
-- Hydrangea arborescens, also known as smooth hydrangea, is loved for its adaptability and reliable blooms. These plants bloom on ‘new wood,’ or this season’s growth. They should be pruned back in early spring which encourages new growth and will result in stronger stems that have less of a tendency to flop. Cutting the stems back to a foot to 2 feet provides a good framework to support blooms. Two of the new "Annabelle" Hydrangea arborescens are "Invincibelle Spirit" and "Incrediball." "Invincibelle Spirit’s" flowers emerge a dark, hot pink that mature to a lighter pink and is small reaching a height of only 3 to 4 feet. ‘Incrediball’ is a remarkable improvement of Annabelle with flowers four times larger on sturdy stems that don’t flop.
-- Hydrangea paniculata, sometimes called "hardy hydrangea," also blooms on this year’s new growth and is a good choice for northern gardens. This is probably the most familiar hydrangea with large elongated clusters of flowers. They can grow to 12 feet tall, but there are newer cultivars that are only 3 to 4 feet tall. "Little Lime" has the same colors as the larger "Limelight," which has large green blossoms with shades of vintage pink. At one-third the size it’s easy to find a space for it in the garden. Early spring pruning to keep them looking tidy is in order. They can be cut back to the ground or if you want slightly taller plants cut back to a foot to 3 feet.
-- Hydrangea petiolaris is a vigorous climbing ornamental vine. It can grow and flower even in our northern climate. The vine was originally from Japan and Korea and blooms in early summer. It can grow to 40 feet so requires a sturdy trellis or fence to climb.
With all the new choices in hydrangeas and their adaptable light requirements, it should be easy to find the right cultivar for your garden.
For horticultural information about shrubs and other horticultural topics, go to the University of Minnesota Extension website extension.umn.edu/gardeninfo/> Master gardeners will answer your gardening questions via a voice-mail service. Call 444-7916, leaving your phone number, name and the nature of your question. A volunteer master gardener will give you a call to speak with you.