Extension Educator, Horticulture
One person's weed may be another person's wildflower. Or is a weed just a plant out of place? Or maybe a weed is a plant whose virtues are yet to be discovered. Or are weeds merely plants having to deal with an unhappy human?
Whatever your definition, weed is a four letter word to gardeners. As Roger Swain says "there are no pacifist gardeners." Once you decide to grow anything, whether it's for food or beauty, you will at one time or another find yourself in hand-to-hand combat with weeds. The battleground is usually bare soil. Dig a new garden bed and all those dormant weed seeds shoot up. By the time August rolls around, weeds may be waist high.
Weeds have a few things in common. They grow rapidly, flower quickly and produce vast quantities of seeds. One good size lambsquarter can supposedly produce 70,000 seeds. Weeds compete with our garden plants for light, nutrients and water.
Once you have decided a plant is a weed, here are some weed control options. First identify the weed. Is it an annual, biennial or a perennial? Annuals such as crabgrass, foxtail, goosegrass, lambsquarter and buttonweed live one growing season and must come back each year from seed. Biennials such as burdock and poison hemlock live two years producing the seed in the second year. With perennials such as dandelions, creeping charlie, and quackgrass the same plant comes back each year.
Whatever you do, do not let weeds go to seed. Remove or mow off the tops before seed is produced. "One year of seeding equals seven years of weeding." Hoe, till or hand pull - These methods only control existing weeds, therefore they must be continued throughout the season. Hoe and till shallowly so as not to damage the roots of desirable plants and bring more weeds seeds to the surface. Perennial weeds will require frequent recutting until the food reserves are depleted.
Mulching controls weeds by preventing light from reaching the weed seeds or seedlings. This method is best for controlling annual weeds. Mulching also conserves moisture, prevents soil crusting, reduces erosion and keeps above ground food crops clean. Organic mulches include wood chips, straw, dry grass clippings and even newspapers. Synthetic mulches such as black polyethylene can be used in vegetable gardens. However they must be picked up every fall and have to be disposed of after a couple of years.
Plant cover crops in the garden. Repeated plantings of buckwheat will help to deplete the weed seed bank. Winter rye can keep weeds from taking over bare soil areas and when tilled in the spring can also enrich the soil.
Plant something. Bare areas will invite weeds. Scalp the lawn and weeds will germinate before the lawn mower sees the garage.
Herbicides. The most common in home gardens are DCPA sold as dacthal and trifluralin sold as Treflan or Preen. Both of these are preemergent herbicides which mean they keep the seed from emerging through the soil. Therefore they do not control existing weeds. Also these herbicides work best against annual grasses. Perennial weeds can be controlled by nonselective herbicides such as glyphosate sold as Round up or Kleenup. It must be applied to actively growing plants to be effective. Since glyphosate has no soil activity, the area may be replanted as soon as the weeds are dead. Because glyphosate is non-selective, do not apply it or let it drift onto desirable plants. When using herbicides, be sure to read and follow all label directions and pay attention to the appropriate crops and the weeds they control.