By Joel M. Lerner
Saturday, April 5, 2008
It's time for your early spring gardening questions.
Q: I have a female and male Ilex verticillata. Each year the female sets berries and they fall off. What might be wrong? -- Lynn
A: Winterberry hollies ( Ilex verticillata) lose their berries for several reasons. One, the plants might be too dry. Winterberry hollies like moist to wet soil, and the berries begin to form in August, usually the driest time in this region. Don't let them dry out. Temperature swings are another potential cause. If berries freeze at night and thaw quickly, they'll drop prematurely. Protect them from morning sun, especially if they're near reflective surfaces, like paving or siding. Finally, you may have lost them to hungry birds.
In your column on dogs and yards, you didn't address the problem of dogs urinating on trees and lawns. This sometimes kills the grass and leaves brown spots in the lawn. How can I get the grass to grow again where dogs urinate? -- Bob M.
First, rake the burned-out grass with a leaf rake. Wash the salts from the urine into the soil with a garden hose, and reseed burned areas. Sprinkle a little compost over the spot to hold moisture and keep the seed in place. Lightly spray the areas with water daily until the seeds germinate. When grass begins to show green, water more deeply and less often, once or twice a week, until it needs mowing.
We plan to plant nandina but want to avoid plants that would harm our cairn terrier. In a previous column, you wrote that nandina was toxic. We checked cybercanine.com and other sites, and nandina was not listed. Where did you learn that it is toxic?
-- Jan and John S.
From the Web site of the American Society for the Prevention of Cruelty to Animals, at http://www.aspca.org/site/PageServer?pagename=pro_apcc_toxic_heavenlybamboo. You will find nandina listed by its common name, heavenly bamboo. But plants with toxic parts can harm pets only if they ingest them. If your pet doesn't gnaw on plants, it will be fine.
I have problems with bare spots under pin oaks and a willow oak, all very large trees. Green moss is replacing the lawn that was growing under them. Why? -- Harry
Shade is the primary reason lawn yields to moss, which is better adapted to shallow rooting and moist shade. To encourage lawn under dense shade trees, allow as much dappled sun through the canopies as possible, which could require a cleanout pruning by a professional arborist. Lower limbs should reach no lower than eight to 10 feet above ground level. That could mean elevating them 12 to 15 feet or higher up the trunk. Cut limbs all the way to the trunk, leaving the branch collar (the widened portion at the base of the branch).
This spring our lawn is inundated with mounds of hills (like anthills) with a hole in the top. We spotted and captured what appeared to be a bee coming out of one of the holes. What can be done to prevent this from happening next spring? What can be done now?
-- Paul and Maggie
You never mentioned the size of the insect, but from your description, it most likely was a cicada-killer wasp. Each hole in the soil is dug by one wasp that hunts for a cicada to sting and paralyze. It lays its eggs on the cicada and leaves the nest, never to return. They generally move on after a short time, a few years at most. They are beneficial insects because they kill cicadas, which are minor pests.
My hellebores are blooming profusely and look great except for the large, drooping green leaves on the ground. Can I trim them? When? -- Betsy
Wait until flowers are fully open to cut old leaves. Now is the time hellebore leaves can be selectively trimmed. While the flowers are open, you can discern flowers, new growth and leaves that have lost ornamental value. Cut only dead and dying leaves.
My lilac bush is very old, and last year it developed something that looks like dandruff -- small, white and flaky (almost like dust) -- that attaches to its trunks. The leaves on several affected branches died and turned brown but didn't drop. What is this, and how do I treat it? -- Marg P.
You are describing scale insects. An infestation can kill a plant in several seasons. Begin to control them now. Insecticide applications may be warranted. Use an application of horticultural oil, just prior to bud break in early April, while the plant is dormant. It will control scale that over-wintered as insects. It requires a thorough treatment of all aboveground plant parts. Always read and follow labeled instructions.
The young crawlers are most vulnerable after they hatch. An ultrafine horticultural oil can be used to kill them in May as flowers fade, or use a systemic insecticide like Orthene or Isotox. To monitor when the crawlers hatched, use black electrical tape wrapped with sticky side out around several branches in the infested areas. Crawlers will stick to the tape.
Each spring, I find my flower beds completely taken over with a weed that reminds me of baby's breath. It is invasive. What can I do to control it?
-- Perki
If the weeds have white flowers, they could be common chickweed ( Stellaria media). It can grow eight to 12 inches tall; loves cool, moist soil in spring and fall; and has an airy look similar to baby's breath (Gypsophila). Take a two-step approach to eradicating it.
These annual weeds are easy to pull, but for best control, they must be pulled now, before they go to seed. Then treat the soil with a corn gluten meal herbicide, such as Corn Weed Blocker or Weed Ban, in spring and fall. Corn gluten meal is a byproduct of a corn milling process. It's a safe material to use in place of the synthetic pre-emergent weed killers. But corn gluten will also keep ornamental seeds, such as lawn, flowers and vegetables, from germinating, so its application must be carefully timed. Follow all labeled directions.
Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, http://www.gardenlerner.com.
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