Blacktop and tree roots don't go together

Tree roots are pushing up the blacktop in my driveway. They're either from two beautiful white pines or two equally beautiful American hollies. They were planted by the original owners of our 1931 house. I love these trees and don't want to hurt them but would like to repair the driveway. Any suggestions?

Except for a few anchor roots, most tree roots are in the top 12-18 inches of soil. Cutting the roots to repave might kill your trees. Removing the driveway and repaving over existing roots may also disrupt the root system enough to kill the trees. You can try patching portions or paving over the existing driveway. The roots will probably continue to grow and expand as long as the trees exist.

Large black flies are swarming inside and outside windows in one room of my new house. They don't live long, but every day I come home to 100 or more dead flies. I thought when we had a cold snap this would eliminate the problem, but no such luck. Help!

Cluster flies commonly enter homes in fall seeking a place to overwinter. They do not breed indoors. These dark gray flies arrive through any crack or cervice around windows and vents. It's likely you have large numbers this year because your house was open during construction. Vacuum up or swat the flies — they're sluggish fliers. Check caulking and weatherstripping for gaps. There is no chemical control. The larvae of cluster flies are actually parasites of earthworms, so they are not associated with filth. However, it's also possible you have blow flies or bottle flies, shiny black flies that feed on dead animals or animal feces. When they appear in a home, you must investigate to see if there is a dead squirrel, mouse, or bird in the attic or wall void. In this case, clean the area to remove the breeding source. For more information and pictures of cluster or blow flies, see our publication, HG 26 Flies In and Around the Home on our website.

University of Maryland Extension's Home and Garden Information Center offers free gardening and pest information. Call 800-342-2507 or send a question to the website at

Plant of the week

Blue mist flower, hardy ageratum

Conoclinium coelestrium

Blue is not a common bloom color this time of year. Yet hardy ageratum, with its fuzzy-headed, old-fashioned look, adds its blue-purple toned flowers and attracts butterflies to the garden from late summer until late in fall. Native to the eastern U.S., hardy ageratum looks similar to the more familiar annual ageratum. Easy to grow, this perennial prefers full sun, though it will tolerate some shade. It's not picky about soil or pH, though it likes some moisture. It spreads slowly into a nice patch, though where too happy it can require serious control. —Ellen Nibali

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