The combination lawn care products known as weed and feed are designed to provide your lawn with a nutrition boost while simultaneously attacking weeds that sprout up and try to choke out grass. With proper timing for applications, these products are very effective, but if applied at the wrong time, they can be dangerous to your lawn. Weed and feed should not be applied any later than spring of the growing year to be helpful to your lawn.
Late spring, generally in April, May or early June, is the best time to apply weed and feed products. This is the time of year when broadleaf weeds, such as dandelions, are actively growing. This active growth means that they are absorbing a lot of water and nutrition from the soil and will therefore absorb the herbicides in the weed and feed along with them. Weed and feed will poison these actively growing leaves while boosting the early-season growing potential of your lawn.
Do Not Apply in Fall
Spring is the only time that the herbicide part of the weed and feed is effective. Once the weeds are fully established (and they certainly are by September), they will not absorb nearly enough of the herbicide to effectively eliminate them. Applying weed and feed this late in the season instead creates a hazard for your lawn and surrounding area. Unabsorbed, the herbicide simply sits in the soil, and over time can gradually poison your grass. Or it will wash away with rainwater and run off into sewers, nearby streams or lakes or even your neighbor's yard, destroying other broadleaf plants that are not weeds.
Fall Lawn Care
September and the rest of the fall bring ideal growing conditions for grass, with cooler temperatures and a lot of rainfall. Therefore, an application of fertilizer without herbicide is key to your lawn's health. Focus on nitrogen this late in the year; a late-season boost of nitrogen helps the grass develop strong roots, preparing it for the tough winter to come. Apply 1 ½ to 2 ½ lbs of nitrogen per 1,000 square feet of lawn space; the phosphorus and potassium that come with this high dose of fertilizer will help, but is not as essential this late in the year.
Weed and Feed Tips
The most important aspect of applying weed and feed is to follow all instructions on your chosen product. Some products need to be diluted, and all products will instruct you of the rate of application for the product. Overuse of weed and feed can result in dangerous runoff or poisoning of other plants. Similarly, all fertilizers can burn grass and cause unsightly damage if overused on the lawn.