Hip, hip, hurray for oakleaf hydrangeas

There are a lot of us native Texans who grew up not knowing about oakleaf hydrangeas (Hydrangea quercifolia) at all. Folks who came from the north knew it as a favorite spring-flowering shrub — much easier to grow than the more common florist, or “mophead,” hydrangeas.

Like many Texas natives, I was introduced to this lovely shrub and I’ve been growing them in our shaded North Texas landscape for 20 or 25 years. I have to say that it has become one of my all-time favorite flowering shrubs for North Texas. For all those folks who look at shade as a curse as their trees grow larger and larger, I offer this as my prime example of why that need not be the case.

Oakleaf hydrangeas are in full bloom right now across Dallas-Fort Worth. The plants grow to be 5 to 6 feet tall and as much as 6 to 8 feet wide, and the creamy white floral spikes are huge — 8 to 12 inches long. They continue to bloom for two or three weeks, at which point the bracts turn to a light tan as they mature. Many gardeners leave them in place or even harvest them later in fall for use in floral designs. Others prefer the more tailored look of trimmed plants.

Because they do grow rather tall, and because their texture can be fairly coarse, oakleaf hydrangeas are probably best when used in open shade, for example, at the bases of large shade trees. They tolerate a bit of morning sun, but they do much better if they’re protected from late morning and afternoon sun in the summer. Their leaves are so large and their growth is so vigorous that the plants may not be able to pull water up to the large leaves quickly enough if they’re exposed to much sunlight. The new growth will wilt each day, and the edges of the leaves are likely to scorch. All of that can be avoided by tucking them back into more shade from the outset.

Oakleaf hydrangeas are plants of all seasons. In addition to their showy spring blooms and dramatically large summer leaves, their fall color can often be exquisite. Leaves turn a rich red or burgundy, often late in the season, and the leaves may hang on for a couple of weeks. In the winter, the bare stems show their interesting shaggy character.

You’ll find oakleaf hydrangeas in most independent retail garden centers right now. They’ve become almost mainstream, which speaks to their zooming popularity. Don’t be surprised if you see named selections in 5-, 7- and 10-gallon pots. Some will have been chosen because they’re more free flowering or compact than the straight species. Others have additional assets. Flower heads of the selection ‘Ruby Slippers,’ for example, turn rosy pink as they age.

Plant oakleaf hydrangeas into well-draining, highly organic soils. While they’ll eventually end up growing in our native North Texas clay after all the organic matter (peat, compost, decomposed bark, rotted manure, etc.) has decayed, they’ll benefit from the head start good soil will provide for them.

Soak your oakleaf hydrangeas regularly with a water breaker on the end of a garden hose. Sprinkler irrigation alone won’t be enough. Drench their soil deeply at least two or three times every week during the summer for the first couple of years. After that, watch them daily when it’s hot and dry, and let them be your indicator of when they need to be watered. When they begin to wilt slightly, soak them again. But remember that their leaves do wilt if the sun hits them, even though the soil may be adequately moist.

We have probably 20 oakleaf hydrangeas scattered about our shaded rural landscape. And we’ve had them for many years. During all of that time, I have never seen an insect bother them. I suppose cotton root rot might get them, but if you add all that organic matter, that soil-borne fungus isn’t likely to be a big issue. It is active only in alkaline soils.

The only problem that I’ve seen other than leaf scorch has been iron chlorosis. Hydrangeas, this one included, love acidic soils. When grown in our alkaline black clay gumbo in and around Fort Worth and its suburbs, the plants may not be able to extract iron from the soil. It becomes insoluble, and the plants’ roots can’t pick it up. Your solution there will be to add an iron and sulfur combination, first to supply additional iron, and (because the sulfur will form dilute sulfuric acid) to help keep the iron in a soluble form as the soil is rendered neutral or at least less alkaline.

Finally, because so many people do love them, we need to pay homage to the popular Mother’s Day florist’s hydrangeas. These “mophead” types are actually much better adapted to the acidic soils and higher humidity of East Texas and the Gulf South. They tend to pout in our North Texas clay gumbo soils and the 100-degree days of mid-summer. But if you want to try one, plant it in shade and in almost pure organic matter. Be ready to water it by hand. No plant will dry out faster.

This story was originally published April 26, 2017 at 11:56 AM with the headline "Hip, hip, hurray for oakleaf hydrangeas."