Pruning Hydrangeas

Lilac or blue colors indicate acidic soil

(From my Gardening Column in the Franklin County Free Press)

We’ve enjoyed the long blooming beauty of the hydrangeas this year. Now the question comes up, as it does every year, about whether they should be pruned now. The answer lies in what species of hydrangea is it. How to Identify Your Hydrangea is a great video from Garden Answers that can help you find out.

Additionally, one of the key factors is if the species blooms on old wood or new wood. Blooming on “old wood” means that buds for the next year form on the wood grown this season. There are some varieties that bloom on both old and new wood. These are offered in patented or trademark series.

Pink color indicate less acidic soil.

Bigleaf hydrangea (Hydrangea macrophylla) is one of the most popular. They are winter hardy in Zones 6-9 but can be killed to the ground in a cold winter, which means no blooms the following summer. These are grown for their pink or blue flowers and bloom on old wood. The blooms fade to green, the natural color of the sepals and are often left on the plant for winter interest.

Big leaf hydrangea blooms fade to green

Often garadeners underestimate the space that hydrangeas need as they grow. If they need to be pruned for size control, do it in July or early August. On mature bushes, prune out one-third of the shoots at the base and shorten the others by about one-half. There are hybrid series that bloom on both.

Oakleaf hydrangea (Hydrangea quercifolia) is hardy in Zones 5-9 and are less likely to be damaged by winter's cold. But they also bloom on old wood, so if they are pruned at the wrong time or browsed by deer, flowering is reduced.

 

Smooth hydrangea (Hydrangea arborescens), a native plant, is hardy in Zones 3-9 and blooms on new wood. They can be cut to the ground in late winter or very early spring and still have blossoms.

 

Panicule hydrangea (Hydrangea paniculata) is hardy in Zones 3-8. It blooms on new wood and can be cut to the ground in late winter or very early spring.

 

Both Mountain (Hydrangea serrata) and Climbing (Hydrangea anomala subsp. petiolaris) species bloom on old growth. Here’s an easy reference chart.

 

ANNABELLE HYDRANGEAS – A Native Plant  (Hydrangea arborescens 'Annabelle' ) 

Annabelle Hydrangea (J Weitzel)

In 1910, young Harriet Kirkpatrick was horseback riding through the woods near her home in Anna, Illinois, when she noticed a wild hydrangea. Its snowball-like blooms were much larger than the others. She dug it up and her family planted it in their garden and shared cuttings with friends. In the 1960's horticulturist J.C. McDaniel propagated it in his nursery and it was introduced as Annabelle after the belle of Anna who discovered it.

ADDING HYDRANGEAS TO THE LANDSCAPE

There  are many different choices for hydrangea plants. If you are looking to add one or more to your landscape, be sure to check the hardiness zone, light requirements, and both the width and height of the plant. Note that for bigleaf hydrangeas, one of the most popular grown for their pink or blue flowers, the color of the bloom depends on the aluminum in the soil which is dependent on soil pH.

CKagan, Master Gardener

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