Q: In Highlands, N.C., the hemlock population has been destroyed. I have four beautiful 12-year-old hemlocks. Is there anything proactive that I can do to prevent the insects from creeping into my trees?

Resa Farmer, Alpharetta

Walter Reeves / AJC Special (ENLARGE)

Wooly adelgid, the insect that kills hemlock trees, looks like white pieces of fluff on the needles.

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A: The most proactive thing you can do is to examine the needles each month for the insect that kills hemlock trees: the wooly adelgid. The creatures are easy to spot, especially in spring. They look like white pieces of fluff among the young needles. There is no need to apply anything until you see the pest on your trees. Keep an eye on other hemlocks in your neighborhood. If you spot adelgids on nearby trees, use a soil drench containing imidacloprid or contact an arborist.

Q: My old purple-leaf plum trees unexpectedly have lots of red-skinned fruit on them. Since it's fashionable to grow edibles in our landscape, how I can tell whether these plums are edible for humans (I don't want to be the tester!).

Catherine Lemons, e-mail

A: The fruit is eminently edible; just don't eat too many or you'll have a big tummy ache. Other gardeners report more fruit on their purple-leaf plums this year than in the past. We know that stress triggers a strong flowering/fruiting response the year after it occurs. My guess is that drought caused the increase in fruit this year.

Q: I would like to improve my carbon footprint by not using a gas-powered mower and letting my Zoysia just grow. It has already gone to seed and still looks good. What damage am I doing to the grass?

John Boyden, e-mail

A: The Zoysia grass will be perfectly happy if you let it grow unmowed. It's best not to fertilize it because this not only consumes natural resources but the grass can develop a harmful thatch layer if it's overfed. If you decide you don't want the puffy appearance of untrimmed Zoysia, consider using a hand-powered push mower. If you mow Zoysia every five days, it won't be hard to mow by hand. If you do it every seven days, the tough stems will make mowing almost impossible. Further, turf grass sequesters carbon in the soil by growing carbon-filled roots into barren soil. One researcher determined that up to 800 pounds of carbon per acre per year is being sequestered by lawns.

Q: On your Web site you mention a brown beetle that "swarms around porch lights at night." I have so many I can barely open my back door. I would like to know what they are and how to get rid of them.

Andrea Cummings, Atlanta

A: The beetle is probably the Southern masked chafer. These brown beetles are about half an inch long. Like Japanese beetles, they emerge from the white, C-shaped grubs you see when you dig the soil each spring. Since they are attracted to light, place a glue board near the light and discard it when it gets full of beetles. Yellow light bulbs are reputed to repel insects but in truth they are only less attractive to night insects than white light bulbs.

Q: Does charcoal dust from my grill have any use in the garden?

Mickey Palmer, e-mail

A: No. Discard it safely after it has cooled.