Tips for pruning hydrangeas

Q. We have several types of hydrangeas and we are wondering if we should prune them this winter. Are some treated differently than others?

David from Youngstown

A. This is a good time to think about pruning, but not necessarily a great time to do it. And yes, there are five major types of hydrangeas grown in Ohio gardens. Some bloom on old wood, meaning the blooms for 2019 were formed last fall on the existing stems. Others will bloom in 2019 on new wood, meaning the blooms are set by mid-spring on new stems. To make it more confusing, we have some that bloom on both old wood and new wood.

So here’s a quick overview of the types, with pruning tips:

Hydrangea arborescens (smooth hydrangea): Blooms on new wood. Commonly pruned down to 2-3 inches tall in the fall. So if you have someone in the house that loves to cut things down – they can do it and you won’t have to worry about losing blooms. It can also be left alone, but the blooms will be smaller and less proper in appearance.

Hydrangea quercifolia (oakleaf hydrangea): Blooms on old wood. Only in years with the coldest winters (well below zero for several days in a row), will this plant lose any blooms. So pruning just after bloom is best. Thinning or taking out not more than 1/3 of the stems in the spring is an acceptable practice as well.

Hydrangea macrophylla (bigleaf hydrangea) and hydrangea serrata (mountain hydrangea) : These are the blue and pink florist type hydrangeas we all love. Some bloom on old wood only. For these, cutting back to the ground in the fall will result in disaster. But cutting back to three buds from the ground is acceptable as long as they are provided some winter protection with mulch to preserve those buds. For those that bloom on old and new wood, I use the same practice for the earliest blooms. Check the plant tag to know which one you have.

Hydrangea anomala (climbing hydrangea): Bloom on old wood. Prune only to shape. These are very heavy vines, thus require support to grow as such. A newer trend is to grow this as a ground cover.

Hydrangea paniculata (panicle hydrangea): Bloom on new wood. Pruning can happen before early April with no problems. I have found that fall pruning after the leaves fall is a good time too. Beware, the more you prune, the larger the flowers will be the next year, subjecting them to bending and breaking during storms. Prune selectively to shape. Do not cut back more than 1/3 at a time.

Visit http://go.osu.edu/hydrangea-facts to download a chart on growing and caring for hydrangeas in Ohio, plus growing tips.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Winter hours for Plant and Pest Diagnostic Clinic vary. Submit questions at 330-533-5538 or drop samples off at the Extension Office in Canfield.