Plant of the week: Smooth Hydrangea

06/25/2014 10:52 AM

From Dennis Patton: Last week I wrote about a great shrub for the landscape: our good old friend the Oakleaf hydrangea. I would like to continue with what will be an on-again/off- again series of great plants for the landscape. This week I want to continue spotlighting the hydrangea family. And, this week I recommend that everyone should have a smooth hydrangea. Now I bet some of you are saying, “What is a smooth hydrangea?” Many of you will recognize it as ‘Annabelle’ hydrangea, an old-fashioned garden plant that is as popular as ever.

Hydrangea arborescens, or smooth hydrangea, is one of the easiest of all shrubs to grow in the landscape. This species of hydrangea is very adaptable to the Kansas City climate. For ideal growth it likes morning sun and afternoon shade. I have also pushed the plant in locations with more sun and it does just fine. Once established the plant is a little drought tolerant, but will do best with supplemental moisture during prolonged dry spells. Like any other plant it will do best in well-drained soil. And that’s pretty much it for plant requirements. So you can see it is pretty easy to grow. It is not a fussy diva like some plants.

The best part about this plant is that pruning is not complicated at all. Everyone can succeed in pruning because you don’t have to worry about making an incorrect cut. Smooth hydrangea is referred to as a cut-back shrub. That is, when growth begins in early spring cut the old stems to the ground. In fact, the only way to mess up pruning is by not cutting it back all the way to the ground. Each spring the plant sends up new shoots from the base. Failure to cut back the plant “hard” (to the ground) will result in stems that are weak and flop over, and produce smaller flower heads. Even when the plant is cut back it will still grow to reach around 3 feet in height. Each of these new vigorous green shoots terminates in a flower which starts to develop in late May and slowly burst into color in mid-June.

Traditionally, the smooth hydrangea flower was pure white. Now new varieties have expanded the palette to include pink shades. Once the flower fades the drying blossom has interest into the fall and winter months. This dried head is even beautiful against a blanket of fresh snow in the dead of winter.

‘Annabelle’ used to be the only variety available for years. Now, with research and breeding, there are a few newer varieties on the market. ‘Incrediball®’ is touted as a new and improved ‘Annabelle’, with larger flowers and sturdier stems. In our demonstration gardens we have not really seen that much difference between the two varieties.

The white color barrier in smooth hydrangeas was broken a few years back with the release of ‘Invincibelle Spirit.’ This is a first of its kind, a pink flower. In our Extension gardens and my own garden this plant is slow to establish, taking a couple of growing seasons to really kick in. The flower color is best in cooler temperatures, as heat washes out the prettier shades of pink into a dusty pink. It is still a nice addition to the garden.

Another pink variety ‘Bella Anna’ has also been released. Here again in our gardens we found this variety to have very weak stem strength and flop to the ground. Our experience was not all that favorable. In fact, the plant died and we did not replace with this variety. Instead we found ‘Invincibelle Spirit’ to do better.

If you don’t have a start of this plant, find a friend and get a one or two. Or take a trip to your local garden center. I am sure you will love this plant as much as I do. In fact, I have it now in several locations in the garden and, as you can see by the pictures of my plants, I couldn’t be more pleased with the results.

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