Ask the green thumb

A gardening expert digs into and answers your homegrown questions.

By Ann Wied
Brookfield, Wisconsin

To Prune or Not to Prune?

At the end of the season when my hydrangea is finished blooming, should I cut it all the way back or leave it alone?
—Maryann McGarry, Massapequa Park, New York

A: That depends on the type of hydrangea you have. Hydrangeas either bloom on current season’s growth or set their flower buds in summer to bloom next spring. Pruning at the wrong time can lead to few or no blooms.

Unsure what kind you have? Make note of when your hydrangea blooms, its flower size and color, growing habit, and leaf shape and fall color. This will help you identify it. Then follow pruning recommendations for that variety.

Keep in mind though, that if properly fertilized and watered, hydrangeas will bloom even if never pruned, although the blooms may be smaller.

Stop Charlie’s Creeping

I know creeping Charlie (at right) is common here, but I have more of it than grass! What can I do?
—Debbie Lee, Belvidere, Illinois

A: Creeping Charlie (Glechoma hederacea), or ground ivy, belongs to the mint family—you can recognize it by its square stems, lipped flowers and faint mint smell. A perennial spread by shallow roots, creeping Charlie likes shady, damp areas. Hand-pulling can be difficult, and many commercial lawn weed killers have little or no effect on it.

But don’t despair! You can control its creep. Keep your lawn vigorous through proper watering, fertilizing and mowing. Mow high, keeping your lawn about 2 to 2-1/2 inches tall—that helps it compete with creeping Charlie and other weeds.

If you want to use a commercial weed killer, make sure you ask your garden center for a product that controls creeping Charlie. The two most effective times to apply it are in fall, just after the first frost, or spring, during flowering. It may take you a full season or more to control. Follow all label directions and safety precautions carefully.

Out, Out, Black Spot!

What are the black spots on my roses? The roses have lost their leaves, though I’ve tried several sprays.
—Lou Kalita, Philadelphia, Pennsylvania

A: Your roses probably have black spot, a common disease that’s caused by a fungus. Black spot needs water to spread, so try these tips to limit problems with it in the future. 1.) Avoid wetting the plants when watering—a soaker hose at the base works best. Use a sprinkler only when the plant surfaces will dry quickly. 2.) Avoid dense plantings and maintain good weed control to improve the air circulation and help leaves dry quickly. 3.) Rake and destroy fallen leaves and, in dry weather, prune out infected canes. Black spot survives from year to year in infected leaves and young canes. 4.) When buying rose plants, select varieties with a high level of black spot resistance.

If your black spot problem is severe, you may want to treat your roses with a fungicide—but first check with a reliable local source to make sure that’s what you’ve got. For you, I recommend the horticultural section of the Penn State Cooperative Extension Web site, and its plant disease fact sheet “Rose Black Spot.” I think you’ll find it helpful. (Connect on our links page.)

What’s This Plant?

Can you help me identify this annual (above)? It grows beautifully in the sun by my mailbox. I received the seeds—black with a white rim—several years ago, and I save seeds from the pods to replant each year.
—Dorothy Parks, Lamar, Missouri

A: This fast-growing beauty is hyacinth bean vine (Dolichos lablab). As you know, it provides color all summer long. Its fragrant, bright pink, purple or white flowers attract butterflies and hummingbirds; you’ll also see purple bean pods and beautiful green foliage. It loves very hot weather and full sun, and it’s fairly drought-tolerant.

A flowering vine that can grow 10 to 15 feet in a single season, this plant needs some type of support to climb. A trellis or fence works well, or as you saw, a mailbox can do the trick.

This plant’s pods and seeds are poisonous, so be sure to wash your hands after handling.

 

Photos: Elizabeth J. Czarapata (Creeping Charlie) Paula Cartwright (photo of Ann Wied)

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