Ask Gardeners Information Service

Every year in May when my Annabelle hydrangeas are leafing out, a little caterpillar “glues” the edges of the top two opposing leaves together to make itself a “house,” which damages the leaves and distorts the subsequent growth and flower bud. Sometimes it merely folds the leaf vertically and seals those edges together. I try to pull the leaf apart gently and remove the caterpillar, but often just have to pinch off the whole thing, which makes the plant lose flower buds. I cannot find any mention of this critter in my references. What is it, and what can I do about it? —M.O., Wilmington, VT

Hydrangea arborescens ‘Annabelle’ is generally a pest-free plant. However, it sounds like your plant probably has a problem with a leaf roller or a leaf tier. Leaf rollers twist or roll a portion of a leaf over themselves and leaf tiers fasten the leaves together with silk threads. Both feed on the leaf and, when full grown, they pupate inside the roll. A small moth emerges after about one week, mates, and begins the cycle again.

Left unchecked, these pests can cause significant damage to plants. Inspect your plant periodically in the spring for the first sign of infestation. Pull off and destroy all affected leaves—caterpillar and all—and be sure to keep the area beneath the plant free of leaf litter. The most successful control is obtained with the use of an oil-based spray insecticide applied to each of the brownish egg masses on the bark or twigs. In late winter, prune the hydrangea to the ground to get rid of any remaining pests, and to promote regrowth and flowering the following year.

I’ve heard that corn gluten meal can be used to control crabgrass. I have looked in both feed and health food stores for it, but no one around here has even heard of it. Can you tell me where to find it and how to apply it? —C.S., New York, NY

Corn gluten meal, a by-product of the milling process that yields corn starch, is an effective, non-toxic, pre-emergent herbicide. It is particularly effective against annual weeds such as crabgrass, but it also prevents germination of perennial weeds such as dandelions, clover, and curly dock. As with most pre-emergent herbicides, corn gluten meal must be applied before weed seeds germinate. Using a standard fertilizer spreader, apply corn gluten in spring, just before weed seeds normally begin sprouting in your area. Reapply sometime after August 15 but before first frost to control weeds germinating in fall. Twenty pounds of corn gluten will treat about 1,000 square feet.

Corn gluten meal can also be spread on flower beds to control weeds. Be aware, however, that for several months after application it will also prevent grass seeds or other purposefully planted seeds from germinating. Don’t use it on newly seeded lawns or on beds where you would like to plant flower or vegetable seeds.

A side benefit to corn gluten is that it contains about 10 percent nitrogen by volume, so it also acts as a slow-release fertilizer. Corn gluten meal is available from Gardens Alive!; e-mail: gardener@gardens-alive.com. A comprehensive list of suppliers throughout the U.S. is available on the Internet.

A good friend of mine named Melissa recently passed away. I read somewhere about a plant called Melissa, which I would like to obtain to commemorate her grave. Can you please tell me about this plant, and where I can find it? —G.R., San Diego, CA

The plant you are referring to is probably Melissa officinalis, also known as lemon balm. The generic name is derived from the Greek word melissa, which means “honey bee” and refers to the plants’ bee-attracting flowers. Lemon balm, a member of the mint family (Lamiaceae), is a lemon-scented perennial herb native to Europe but naturalized in most parts of the world. The plant is grown primarily for its sweet-scented foliage, although it does produce small white, yellowish, or pinkish flowers that bloom from June to October on erect stems up to 24 inches tall.

This plant is easy to grow from seed, but many nurseries and garden centers carry reasonably-priced starter plants in the spring. V.J. Billings, owner of Mountain Valley Growers, Inc., in Squaw Valley, California, notes that lemon balm does best in full sun and well-drained soil and warns, “This plant readily re-seeds itself, so cut it back severely two to three times throughout the season to keep it from spreading out of control.” For lemon balm seeds, call Shepherd’s Garden Seeds in Torrington, Connecticut, at (860) 482-3638. To order plants by mail, contact Mountain Valley Growers, Inc. at (209) 338-2775, or check out their website at  http://www.mountainvalleygrowers.com