A few years ago, back during the drought, I was ready to give up on hydrangeas. They were the coal-mine canaries of my yard, the first to droop if they were dry, and after the first few years not blooming much.
They also received different amounts of filtered sun so they were of different sizes. My enthusiastic but haphazard pruning hadn’t helped, either.
Looking for inspiration, I walked around downtown Napa. I noticed that few of my neighbors seemed to care about symmetry, and their lovely hydrangeas were of differing shapes and sizes.
The varieties were different, too. Lacecap and mophead types (Hydrangea macrophylla) often appeared in the same yard, and by the time I reached the commercial area of Napa, I observed another specimen much in vogue—the oakleaf hydrangea (Hydrangea quercifolia).
I decided to replace one hydrangea at the end of the row with the oakleaf variety. It was so obviously different that symmetry would be a non-issue. And it was tall, with large, deeply lobed leaves and showy cones of creamy flowers.
I also learned that one reason the oakleaf hydrangea is so popular around local hotels and restaurants is that it requires less water than other varieties. In the winter, its peeling bark and bronze leaves provide some interest.
Oakleaf hydrangea flowers on old growth, so it should be pruned after its first bloom. This winter, I broke that rule and did a light pruning to shape it, but I made sure to keep a lot of buds on the stalks. Helped by this year’s generous rainfall, my oakleaf hydrangea should be more luxuriant than ever this summer.
Hydrangeas are beautiful shrubs that reward the home gardener with a spectacular flower display if they are watered and fertilized adequately and pruned at the right time. Keep the soil moist, not wet, to a depth of one inch. (Oakleafs require less water.) A layer of mulch will keep the soil moist longer. Hydrangeas like sun; filtered sun is best for keeping their color.
Fertilizing is also important. When you plant a hydrangea, dig a hole three times the size of the container. Then fill the planting hole with a 50/50 blend of soil and an acidic amendment, such as a commercial soil mix for camellias and azaleas. Dig in some compost to improve texture. Plant the shrub so it is level with the ground and add a one- to two-inch layer of mulch.
Fertilize in early spring or summer. The bloom color of some varieties reflects how acidic or alkaline the soil is. Alkaline or neutral soils produce pink flowers; acid soils produce blue flowers.
To produce blue flowers, you may need to acidify the soil. Use a water-soluble acidic fertilizer with few or no phosphates, since phosphates are alkaline. In the fall, apply one teaspoon of aluminum sulfate per foot of plant height. Mix with water and drench the soil. Don’t expect a change overnight.
For pink flowers, you need soil with a pH of 7.0 to 7.5. If necessary, adjust with a balanced fertilizer, but add superphosphates in the fall or winter. It is easier to turn flowers pink than blue. Don’t fertilize after August, as hydrangeas are preparing for dormancy.
As for pruning, first determine if your hydrangea blooms on new or old wood. Old-wood bloomers (hydrangeas that produce buds on the previous season’s stems), such as broadleaf hydrangeas and oakleaf hydrangeas, should be pruned after they bloom. Remove weak, dead or crossing stems. (Scrape your knife along a stem; if you don’t see green, it’s dead.) Make sure to leave green stems, as they will be setting buds. With these varieties, prune only for shape and remove no more than 30 percent.
New-wood bloomers such as PeeGee (Hydrangea paniculata) and Annabelle (Hydrangea arborescens) produce buds on new stems. They can be pruned any time except when they are preparing to bloom. You can prune these varieties more aggressively but avoid taking them down to the ground in fall. They can have large flower heads that need support from some old growth.
Hydrangea leaves and buds are poisonous if eaten. According to the California Master Gardener Handbook, animal poisonings were reported in older literature, but no recent cases have been reported. Wear gloves when pruning to prevent contact dermatitis.
With just a little care, hydrangeas will reward you with color all summer.
Workshop: U. C. Master Gardeners of Napa County will conduct a workshop on “Growing Hydrangeas” on Saturday, May 6, from 9-11 a.m., at University of California Cooperative Extension, 1710 Soscol Ave., Napa. Hydrangeas add style and color to the home garden with their variety of foliage textures, bloom shades and size options. Learn about caring for, pruning and propagating hydrangeas for beautiful outcomes. Vigorous and long-lived, hydrangeas reward the home gardener with extravagant results.Online registration (credit card only); Mail-in registration (check only or drop off cash payment).