The Best Time to Put Down Weed & Feed

Combination weed and feed products may seem like a time- and effort-saving solution to your lawn problems. They promise to provide important nutrients to your grass, keeping it green and lush while killing unsightly nuisance weeds. However, applying weed and feed products at the wrong time of year, or on the wrong kind of lawn, can keep them from working correctly. Learn when to use weed and feed and when to choose an alternative to keep your grass green and your lawn safe.

Weed and feed products contain broadleaf herbicides intended to kill green, leafy plants and leave your grass intact. Some products also contain pre-emergent herbicides designed to kill crabgrass and other grassy weeds. Manufacturers combine these chemicals with fertilizers to provide nutrients for the growing lawn. To work properly, each type of weed and feed must be applied at the correct time.

Crabgrass and related weeds are best killed using pre-emergent herbicides, which keep the weeds from growing, rather than post-emergent types, which kill on contact. Weed and feed products meant to control weeds before they grow should be applied early in the growing season, before the weeds have a chance to emerge. Pre-emergent herbicides don't work on weeds that already have a head start.

Post-emergent herbicides kill broad-leaf plants on contact, but don't usually adhere to grass blades. Applying too much of this kind of weed and feed can kill your grass. Apply these products according to the manufacturer's instructions after the weeds have already emerged. You may wish to wait a few days after mowing to ensure enough weed growth for the herbicide to work.

Apply weed and feed products to grass mowed at a medium height once or twice per year. Avoid using these products during a drought, since they are incompatible with lawn watering. Spread the chemicals uniformly over wet grass. Don't water the lawn for at least two days and avoid planting new grass or aerating the lawn for four weeks.

Weed and feed products contain herbicides that can harm humans, wild plants and animals. According to Thurston County Public Health and Social Services and Texas A&M University, these chemicals frequently get into groundwater and are tracked inside by humans and pets. These chemicals have been linked to cancer, neurological problems and reproductive conditions. Avoid using weed and feed if you have other alternatives.

While weed and feed is convenient, it isn't an economical or environmentally-friendly lawn-care choice. Consider fertilizing in the fall and weeding by hand as needed. Chopped grass mulch from mowing can reduce weed growth while providing important nutrients, acting as a natural weed and feed. According to Iowa State University, corn gluten meal can also control weeds while feeding grass, without toxic side effects.