I tend to agree with Ralph Waldo Emerson when he defined a weed as a plant whose virtues have not yet been discovered. But unless we make use of their virtues, it is important to control weeds such as foxtail, purslane, henbit, knotweed and common lambsquarter, all of which will go to seed between now and fall in our region.

Control of spring and summer germinating weeds is best accomplished before they emerge. Early treatment is the only way to get almost complete control over weeds, and it's just about impossible to ward them off any other way.

So what can you do if you can't treat for control now? You can pull weeds by hand, mulch them or use a post-emergent herbicide in large or overgrown areas. The idea is to control them before they go to seed.

Pull weeds when they're small--before they multiply. Every time you pass by the beds, pluck a few. Do it while they're young and they'll never self-sow enough to become a major problem. If your spring-germinating, summer-seeding weeds are numerous and have gone to seed, write on the March 1, 2000, slot of your calendar: "Treat yard with pre-emergent weed control while the forsythia is in bloom." Then go outside and pull the existing weeds, keeping as much of the seed from spreading as possible.

If the weeds are too invasive to pull by hand, a control is glyphosate, sold under the names Kleenup, Roundup or Finale. It biodegrades quickly, and you can safely spray it over the roots of mature shade trees to control weeds and keep them from coming back. This nonselective herbicide will kill any plant it contacts, so it can't be used on the lawn or the leaves of any other plants that you want to keep. Read and follow labeled instructions before application.

Glyphosate, however, works slowly. In the seven days it takes to perform fully, many annual weeds can go to seed. If quick knockdown is preferred, another nonselective herbicide that wilts them in hours is Super Fast by Safer Company. It's a potassium salt that won't harm the environment, but burns the foliage and turns it brown immediately. But be careful--a gust of wind while you're spraying could blow it onto ornamentals.

A spring and fall pre-emergent herbicide treatment can greatly reduce the need to hand-weed at this time of year. You can try Team, Barricade or a kindred pre-emergent weed control in spring. Apply Gallery or Preen in the fall to keep seeds from germinating in winter, such as dandelion, clover, plantain and thistle.

For more detailed advice on herbicides, call the Cooperative Extension Service in your area. Following are numbers for offices in this area:

Cooperative extension: Maryland 1-800-342-2507, which is toll-free in Maryland only. ; Washington 202-274-7158; Arlington 703-228-6414; Fairfax 703-324-8556; Loudoun 703-777-0373; Prince William 703-792-6285.

Counties outside of Maryland may call Maryland's Home and Garden Information Center at 410-531-1757. Extension service also numbers can be found on the Web page for the University of Maryland's College of Agriculture and Natural Resources (www.agnr.umd.edu) by clicking on the link to "Maryland Cooperative Extension."

Another practical weed control is mulch, which is any material that can be laid in the beds to act as a protective covering, reduce evaporation, prevent erosion, control weeds or enrich the soil. It can be compost, straw, salt hay, ground corn cobs, pine bark nuggets, cocoa bean hulls, shredded hardwood bark, licorice root, wood chips, newspaper, landscape fabric, stone and even shredded tires. I personally prefer organic, partially composted materials.

If you pick up free mulch, as many county governments offer this time of year, it may contain weed seeds. This material needs to be composted for another three months or so and will make great mulch in fall.

Compost makes an excellent mulch that enriches the soil as it protects. Lay it two inches thick onto beds, but don't pile it against the bark of trees or shrubs. Placing a one-inch veneer of your favorite ornamental mulch on top of the compost to dress up the property for mid-summer is a valuable step toward drought and winter protection.

I have told you how to get rid of weeds, but there is a time and place for everything, and weeds are no exception. They can be beneficial to reduce soil erosion on land where cultivated plants don't thrive. They can also provide food and shelter for birds and other wildlife.

I don't consider some plants weeds, even though they are generally characterized that way by most gardeners.

Dandelions, for example, when young and tender, are at their best for making wine and for use in salads. If you use them for food, you might not have enough in your lawn and may have to get permission to harvest the neighborhood lawns. You can even buy them by the pound at some grocery stores.

Chicory roots can be pulverized to make a coffee substitute. You can eat purslane. The red, fleshy stems, thick succulent leaves and small yellow flowers of this prostrate grower can be eaten in a salad or cooked like spinach, but don't eat the roots.

If you plan to eat weeds, do not use herbicides or insecticides on them. Before you eat any, be sure to get a positive identification from a garden center, plant clinic or Cooperative Extension Service. Look for a good book on the subject, like "Eat the Weeds" by Ben Charles Harris (Keats Publishing, 1995).

Lerner is president of Environmental Design in Capitol View Park, Md. His e-mail address is lernscap@erols.com.