February 2018

Hydrangea primer: what to prune when, why and how in the Indiana and Midwest garden

Quick Fire is one of the first Hydrangea paniculatas to bloom. Photo courtesy Proven Winners/ColorChoice

Quick Fire is one of the first Hydrangea paniculatas to bloom. Photo courtesy Proven Winners/ColorChoice

About this time last year, I wrote a piece for Angie’s List Magazine (see below) about hydrangeas, including tips on growing and pruning them.

Tim Wood, who hunts plants for Spring Meadow Nursery in Grand Haven, Mich., has published another hydrangea primer that many Indiana gardeners will find helpful, too. Known as the Plant Hunter, Wood’s latest newsletter talks about growing hydrangeas in the Midwest and offers some great pruning tips for those desirable big-leaf and re-blooming hydrangeas (Hydrangea macrophylla).

He reminds us that the most reliable hydrangeas for most of the Midwest are the native Hydrangea arborescens, of which the white mophead ‘Annabelle’ is probably the most familiar. ‘White Dome,’ with delicate, white lacecap flowers, also is a H. arborescens. ‘White Dome’ is a Spring Meadow introduction, which is marketed under the Proven Winners/ColorChoice brand. The nursery also introduced ‘Invincibelle Spirit,’ the first pink-blooming Hydrangea arborescens.

You just can’t beat the panicle hydrangeas (H. paniculata) for reliability, beauty and ease of care. The popular and best selling ‘Limelight’ is another Spring Meadow introduction. Two other stunners are Pinky Winky and Quick Fire.

Angie’s List article

We’re heading in to high season for hydrangeas, one of the showier shrubs in the landscape. With their moptop and lacecap flowers, these plants grab centerstage in the summer garden. And, they hold a place for two more acts as their flowers dry to autumn hues, then winter whites.

There are two basic types of hydrangeas (Hydrangea), those that bloom on year-old growth and those that bloom on current season growth.

The big-leaf hydrangea (H.  macrophylla) forms its flower buds in late summer and fall. In the upper Midwest and other cold climates, freezing temperatures in late spring frequently zap these buds, causing the plant to grow leaves, but no blooms.

You can reduce this threat by siting a big leaf hydrangea where it is buffered from drying winds and freezing temperatures. Many northern gardeners protect it by making a sleeve to fit around the plant and filling it with leaves in fall. The leaf-stuffed sleeve stays on the plant until spring, when there’s no danger of a hard freeze. The sleeve can be made of cloth, such as burlap, or it can be a plastic trash can with the bottom cut out.

The big-leaf hydrangea is better suited for the more moderate climates in the West, South and Southeast. H. serrata is another popular hydrangea that blooms on year-old growth and can be susceptible to flower bud damage from cold temperatures.

If you need to prune these hydrangeas, or the native oakleaf hydrangea (H. quercifolia), do so within a month after it blooms. Although the oakleaf blooms on year-old growth, it does so later in the season so its flower buds are less likely to be damaged by late spring temperatures, making it more reliable in northern gardens.

Breeders have begun marketing big-leaf hydrangeas that bloom on new and old growth. Endless Summer™ is probably the best known in this new breed.

The color of the flowers on H. macrophylla depends on the soil. Acidic soil produces flowers in the blue range and hydrangeas planted in alkaline soil have blooms in the pink palette. You can add alumninum sulphate to hydrangeas planted in alkaline soil to turn them blue and lime to those planted in acidic soil to turn them pink.

The most reliable selections for cold climates are the native smooth-leaf hydrangea (H. arborescens) and H. paniculata, commonly referred to as peegee hydrangea, from Asia. Both of these hydrangeas bloom on current season growth, which means you can prune them in spring without cutting of summer’s flowers. The flower colors on these hydrangeas cannot be altered by soil additives. These bloom on current season’s growth — what grows this year blooms this year.

Prune H. arborescens to the ground in late winter or early spring. Prune H. paniculata as needed as needed for shaping or cleaning up damaged branches in late winter or early spring.

Popular smooth-leaf hydrangeas are the mop-top ‘Annabelle’ and the lace-cap ‘White Dome.’ Invincebell Spirit, another breeding breakthrough, is the first pink-blooming H. arborescens moptop. It will be marketed under the Proven Winners ColorChoice brand in spring of 2010.

‘PeeGee’, ‘Tardiva’, ‘Grandiflora’, ‘Pinky Winky’, Quickfire and ‘Limelight’, are good choices for H. paniculata. These form cone-shaped flowers, called panicles, that take on various hues of white, green or pink. These tolerate more sun that other hydrangeas.

Plant hydrangeas in shade to part sun. They tolerate full sun, but will need supplemental watering. All hydrangeas do best in soil rich in organic matter. The native smooth-leaf hydrangea can handle fairly wet soil to dry.

Apply about an inch of compost, rotted manure or other organic matter to the soil around hydrangeas in spring as they start to develop their leaves. If using a soil additive or hydrangea fertilizer, always read and follow the label directions.


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