As we go deeper into fall, I find myself knee-deep in reader e-mails. I'll use this weekend's column to answer some of them.
Q: We had four lovely tropical hibiscus plants in large pots on our patio this summer and would like to keep them alive over the winter. We plan to store them in our basement, which is dry and cool. Should we do this, and should we cut them back or store them as they are?--Richard L. Fields
A: I prefer treating hibiscus like a houseplant--keeping them upstairs, not stored away. Before you take your plants in, cut them back substantially, leaving short branches. Then, because hibiscus is susceptible to many diseases and insects, mix an insecticidal soap with a light oil, such as Sun Oil, and spray the plants. Some experts recommend spraying the soil with an insecticide such as Diazanon or Dursban as a preventive measure. But I think it's sufficient to pull up the root balls to check thoroughly; if you see no insects, don't spray.
Then take the plants in and check periodically for aphids, whitefly and other insects. Put the plants in a sunny window and water when the soil dries. Keep the plants away from heat vents. If you can, place them on shallow pans filled with gravel and cover the gravel with water. Don't fertilize now. Leaves will grow, but not vigorously as they did on your patio. In spring, fertilize at every other watering with a water-soluble fertilizer, such as Peters Plant Food. Put the plants outdoors after the danger of frost is past, about May 1.
Q: White oak acorns have embedded themselves into our lawn almost wall to wall. Raking gets some, but many have taken root. Short of getting down on our hands and knees, how do we get rid of these undesirables?--Arne Bang
A: Maintaining a lawn in the shade of an oak tree is difficult enough without acorns. But don't worry about your lawn becoming a tree farm: Oak tree seedlings can't grow at the 2 1/2-to-3-inch mowing height of most lawns. Where there is no lawn, however, you'll have to pull them by hand. Polypropylene rakes with wide tines will grab a lot more acorns than a spring steel wire rake. The squirrels will eat some acorns, but they'll also plant them in your flower beds. You'll be pulling those next spring as weeds.
Q: May I use the ashes from our grill--regular charcoal, without lighter fluid used--as fertilizer? What about ashes from prefabricated fireplace logs?
A: While charcoal ashes, as long as no starter fluid was added by you or the factory, are excellent for digging deep into your garden to improve drainage, they may not be as rich in potassium and phosphorous as wood ash from hardwoods. Ashes don't need to be composted first, but never sprinkle them over established lawns. As for prefabricated-log ashes, don't use them in the garden.
Q: We have a small shaded lawn that is thin at best, but looked fairly good up until Labor Day. Then something inspired the local crows to tear it up, leaving large bare spots. Would it be futile to seed these patches?--Carrie Andrews
A: The crows are probably feeding on insects and seeds. Soon they will migrate and their feeding should stop. That would be an excellent time to sprinkle compost over the patches and lay down a cool-season grass seed. You may never see this crow phenomenon again, or you could see it annually when they return and remember the rich pickings. If your lawn is not too large, next year you might try one of the castor-oil-based deterrents designed to make plants and insects taste yucky to wildlife. Mole-med and Mole Away are examples. When sprayed on the food source, they deter a variety of wildlife.
Q: I had a large, heavy-duty arbor built to support climbing hydrangeas, one on the west side and one on the east. They have grown, but every year their leaves curl and turn black for a period. A county extension agent determined they had mites. I applied an insecticidal oil this year. What can I do this fall to make them come back strong in the spring? When do they bloom?--Pat Lee
A: Your climbing hydrangeas may be stressed. I don't know them to have disease or insect problems, except in poorly drained or dry soils. They like moist, well-drained soil with lots of compost and north or east siting. Mulch the roots now with two inches of compost, your own or something like Leafgrow, available at garden centers. If the soil is hard, vertically mulch by digging leaf compost down four or five inches around the outer roots. Irrigate in drought, especially in full sun.
You can treat with a fish meal, humic acid or vitamin product, such as SuperThrive or Roots. Hydrangeas bloom an off-white color in late June, but are valued more as a full-growing clinging vine than for showy flowers.
Q: Where can I buy trillium plants?
A: I'm surprised you can't find trilliums locally because they have become fairly popular for woodland gardens. Garden centers usually stock them in the spring. I use one grower who has a selection of rare plants. So if you're into some of the more obscure species, give him a call. Owner and plant collector Barry Glick lists eight species of trillium. His company is Sunshine Farm and Gardens in Renick, W.Va.; call 304-497-2208. Check his Web site (www.gardenweb.com/sunshine).
Q: The roots of a 20-year-old silver maple in my back yard have started to emerge at the top of the ground. They extend as far out as 15 feet from the trunk, into the lawn. Should I mulch about six to eight feet out from the trunk in a circle around the tree? How bad will the roots get? Should I cut down the tree?--Jeff Shaffer
A: This is one of the more disputed trees in the landscape. Builders plant silver maples because they're tough and fast-growing. Homeowners dislike them mainly because of surface roots. I recommend a compromise.
Mulch a wide bed around the base of the tree to take the worst surface roots out of the lawn. Then, with an ax, chop surface roots that are in the lawn farther away from the tree and lift them out. Fill the furrows those roots created, and other uneven areas, with organic material and reseed. This will be ongoing once every couple of years but is probably a better solution than cutting the tree down. If the bed around the tree gets so large that it starts looking bare, plant some shade-tolerant perennials in it to add color and interest.
Lerner is president of Environmental Design in Capitol View Park, Md. His e-mail address is firstname.lastname@example.org