Lush, green lawns are inviting places to spend summer days. Unfortunately, the ingredients to a beautiful lawn -- such as regular water and fertilizer -- are also just what weeds need to grow as well. If you time it right, combining weed control with an annual fertilizer application is one strategy that can keep weeds from taking over your lawn.
The best time to fertilize the lawn is in fall as it is preparing for winter hibernation and increasing root development. The number of roots multiplies and roots grow deeper into the soil than in the spring or summer. Fall root development leads to a healthier lawn in the spring. Thick roots and healthy grass leave little room for weeds to sprout and grow at any time.
Even the thickest, healthiest lawn can leave some room for persistent weeds. The key to getting rid of them is to know what kind of weed needs to be eliminated. Annual weeds grow for one season before going to seed. Perennial weeds will come back year after year without needing to produce seeds. Weeds that resemble lawn grass also need different treatment than broadleaf weeds. Examine the lawn frequently to determine what the weed control needs are every year. Unknown weeds can be taken to a garden center or horticulture extension office for identification.
Lawns that have grass-like weeds, annual weeds, or do not have visible weeds benefit from a pre-emergent weed killer. This type of weed control interferes with the ability of seedlings to establish healthy roots. Seeds will sprout, but will die before becoming large enough to be seen in the lawn. Plants with established roots, such as lawn grass, are not harmed by pre-emergent treatments. This also means that perennial weeds will not be affected. Pre-emergent weed killers are best applied with fall fertilization or in the early spring, just as the lawn is coming out of winter hibernation.
Broad leaf weeds that are firmly established in the lawn are best removed by a systemic weed killer. Root systems absorb systemic treatments along with water and nutrients. The weed killer then attacks the weed from the inside, where it destroys the plant’s ability to grow. Systemic weed killers work best if applied with fertilizer, because roots will detect the newly available nutrients and absorb as much as possible, drawing in more weed killer. Systemic weed killers will not prevent weeds from growing and only affect weeds that are actively growing, which makes early fall the best time to use them. They do not work on grassy weeds -- these weeds are too close to the lawn grass that weed killers are designed to protect.