Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern California Coastal & Inland Valleys
April, 2009
Regional Report

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A properly pruned hydrangea will produce an abundance of blooms summer through fall.


Henry's wife loves hydrangeas. She would like nothing more than to have the entire shady side of the garden planted with dozens of these seemingly easy-to-grow shrubs. I believe she likes them as cut flowers because they last so long in arrangements. As a gardener, I like them because they can be encouraged to change color, like a chameleon. How can one plant garner so much interest?

First of all, hydrangeas are not as easy to grow as you might imagine. Plant two side by side and one will flourish while the other languishes. I find them a bit fussy, but if you have the green thumb for them, no plant is more rewarding. Hydrangea macrophylla is the garden variety that does best in Northern California. It will grow to eight feet tall, or more. Florist varieties don't do as well in the ground as the macrophylla, but will flourish in containers year after year.

The huge clusters of flowers are the main attraction. There are two kinds of flowers on each hydrangea bloom; the sterile flowers are the large, flat sepals that make up the main body of the cluster. The fertile flowers are tiny blossoms riding on top of the flat petals. Lace cap hydrangeas have fertile flowers in the center of the cluster, surrounded by the sterile flowers. There are climbing hydrangeas (H. anomala petiolaris), hydrangeas with small flower heads (H. paniculata, sometimes called Peegee), oak leaf, fuzzy leaf, and many, many more varieties on the market.

The color of the flowers can be tweaked by changing the pH of the soil, but don't expect instantaneous results. It will take one entire season to change the color of the flowers. Hydrangeas that are grown in acid soil will produce blue flowers, while those that reside in alkaline soil will produce pink or red flowers. Aluminum sulfate will change the pH to acid, while superphosphate will create an alkaline environment. You can add aluminum sulfate to one side of the plant and superphosphate to the other side and create both colors on the same shrub. Mix the two products and you create purple flowers.

It's very easy to propagate hydrangeas. Softwood or hardwood cuttings are taken while the plant is dormant. Select a cutting about 6 to 10 inches long with at least three leaf scars and try to remember which end is "up." You can mark it with tape or a nick of your clippers. Make a flat cut just below the bottom leaf scar, then dip the tip into rooting hormone and place in a pot filled with damp sand, vermiculite, or fresh potting soil. The cutting should be buried at least half way up the stem. Cover the prepared cutting with a plastic bag to keep in the humidity. When you begin to see new leaves forming, you know that you have been successful.

For years I have been pruning hydrangeas incorrectly. I tried to prune them like roses, taking off far too much wood. My friend Ricky, head gardener at Sunset Magazine, told me that the secret is to leave as many branches as possible, then to encourage multiple branching at the top of each branch. This makes sense because the flowers form on wood that is two years old. The more branches you have, the more flowers you will get. Pruning hydrangeas should be done at the very end of the dormant season. Fertilize with a balanced product just after pruning to encourage new growth.

To have the best success drying cut hydrangea flowers, select those with the fertile flowers tightly closed. I like to "water dry" my hydrangea flowers, soaking the stems in a deep vase until the flower has dried to the touch. It takes several weeks, but they don't wilt like they sometimes do if you hang them upside down. If the color fades, use spray paint lightly.

Hydrangeas like a very wet soil, so if you have a boggy spot that never fully dries out in your garden consider planting these excellent shrubs. You will make Mrs. Henry very, very happy....

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