Green Scene: Pruning tips, groundhog repellent and other gardening advice

By Joel M. Lerner
Saturday, March 13, 2010; E03

As daylight saving time begins this weekend, it's a reminder that spring is just around the corner. So we have an assortment of questions that spans the winter-spring boundary.

Q: How do I prune shrubs such as pieris japonica and nandina? Their branches are drooping. Is it better to prune or to tie them to a post to make them upright? -- Joanne Gillespie

A: Prune branches that have snapped, and prune off bent branches or stems that did not return to a satisfactory upright position as the weather warmed. A Japanese pieris will renew from the point at which it snapped. This process could take until July or August, depending on the extent of damage. If branches were only bent, they might already have started to return to their original form. Nandina stems are flexible, and I've witnessed little more than some cane bending and expected defoliation. Give them until August to recover. If your nandinas are vigorous growers, this could be time to cut out some older canes at the base. Do hard, corrective pruning now, before new growth begins.

Q: I noticed a big tunnel, bump and hole about three to four inches in diameter in my yard. What could it be, and how do we get rid of it? It's too big for rats or chipmunks. -- Fred Mopsik

A: It might be a sinkhole. But if there is soil piled near the hole, it was probably made by a groundhog, the largest burrowing rodent. Also called woodchucks (Marmota monax), they mostly eat herbaceous plants, especially produce, and are a nightmare for gardeners who want manicured landscapes. They are tough to control; in many areas live trapping for release elsewhere is not permitted. Such live-caught wildlife is often euthanized.

Groundhogs seldom tunnel deeper than four feet but will dig a distance of 15 to 50 feet, depending on the size of the colony. There can be multiple burrows. There are always five to eight ways groundhogs enter and exit their network of tunnels. Discourage them by laying heavy wire mesh fence that has no larger than one-half to one-inch openings. Cut one-square-foot pieces and bury them in soil over openings to all the tunnels you can find. Use a safe groundhog repellent as treatment around wire-covered holes. One groundhog repellent that is safe and approved for organic growers is Messina Wildlife's Groundhog Stopper.

Q: For the past month or so, I've had scampering activity in my attic but haven't seen anything. We live in the suburbs and have bird feeders and a compost pile. What else might attract these critters? -- Gail Fisher

A: Your comfortable space is the attraction. Learn more about living with wildlife at You also can contact pest-control companies that specialize in wildlife. Guidelines I've seen for keeping wildlife out of houses are to close off all points of entry by caulking all openings, regardless of size, around the foundation, siding, eaves, roofline and vents installed near the top of the roof for air circulation. Cover larger openings with galvanized or plastic screening.

Q: Some tree trunks in front of our home have what appear to be unsightly moss and lichens growing up about six feet from the base. How can we remove these without damaging the trees? -- Alan and Therese Delhomme

A: The tree trunks have what you suspect, moss and lichen growth, which are often mistaken as plant diseases. Their presence indicates information about the trees' siting. Lichens are a combination of green algae and fungus and are an environmental indicator. These plants are sensitive to air pollution and will only grow where the air is clean and moist. If the aesthetics bother you, try to lessen the moss and lichens by increasing drainage and air circulation by cutting away branches or small trees or shrubs to reduce shade and open the area up to prevailing winds.

Q: We have powder post beetles in our hardwood flooring. The wood was kiln-dried, which would have killed any eggs or larvae. Where could they have come from? -- Susan Crawford

A: Powder post beetles feed only on dead wood, and adult beetles will eat unfinished lumber. You will not have powder post beetles from properly kiln-dried lumber. Damage appears as a collection of tiny pinholes where beetles have emerged from the wood. They are brought into homes in infested wood or furnishings. This is why you should never bring in firewood for more than two days. Adults can fly from infested woodpiles in the yard, so store firewood well away from walls of your house.

Q: Could you recommend a hydrangea? The house has a brick wall; the area is quite protected and gets almost full sun. I am fond of mopheads with blue flowers. -- Valeria Roman

A: Some varieties of the big leaf mophead hydrangea (H. macrophylla) to look for, among the thousands available, are Endless Summer, which blooms on the current year's growth with many flowering buds; Hillier Blue, which is hardy and produces many flowers; Otaksa, which has extremely large blooms; and Nikko Blue, which has deep green foliage and deep blue sterile flowers. Wildenstein flowers early, re-blooms and has large round heads. Mousseline is pastel blue and can reach five feet. The shade of blue depends on soil pH and aluminum content. Acidify with aluminum sulfate sprinkled around the base of plant if it's necessary to turn hydrangea flowers from red to blue. Get suggestions from garden centers on other hybrids.

Q: You have written that use of clumping kitty litter on ice "can be dangerous to your pet's health." Please clarify that. -- Arpi Sahr

A: Clumping litter commonly available today is a clay-based material (sodium bentonite). I have found as many people saying it is harmless as dangerous. The theory is that it can leave a clay coating in your cat's gastrointestinal tract that is not digested and builds up in their system as pets lick themselves clean. Cats also inhale the silica dust, which can coat their lungs. Sodium bentonite is considered harmful to the environment because it is strip-mined. The jury is out on a definitive answer. Many pet owners have perfectly healthy cats for 17 to 18 years that use clay litter. But if you are concerned about clay litter, try some "green" materials. I have seen shredded newspaper (virtually all ink is now soy based and safe), wheat-based Swheat Scoop, corn-based World's Best Cat Litter, pine-based Feline Pine, recycled paper-based PaPurr and corn fiber-based Arm & Hammer Essentials.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.

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