Weeds can be a problem in lawns, and when establishing new grass, the use of weed killers is a delicate matter. As the new grass emerges, weeds may emerge as well, but ridding the lawn of weeds at this stage of a lawn's development may not be best handled with weed killers.
Your New Grass
Whether the new grass plantings are for low-traffic, ornamental landscapes or for high-traffic durable turfs, new grasses are not as strong as established grasses. Planting new grass from seed will take longer to develop than ready-made sod, but both types of new grass need time to establish their roots in the soil. Prior to addressing weed problems with chemicals, it is better to handpick weeds and give the new lawn a few mowings before treating it with weed killer.
Preparing the Soil
To prevent or decrease the emergence of weeds on a new lawn, soil preparation prior to planting grass seeds or sod is important to having a virtually weed-free lawn. Begin a new lawn area by removing plantings and weeds from the soil. Preparing the soil includes loosening and raking out the soil, mixing in soil enhancements and fertilizers and sprinkling the area with water to moisten the soil and to activate some of the soil additives to improve its overall quality.
Weed Killers Before the Grass
After the soil is physically prepared for new grass, applying a preemergence weed killer may prevent the remaining weed seeds and roots from developing into new weeds.
Selecting a brand of weed killer that will not harm the type of grass intended for the lawn is important to prevent damage to the new grass. After applying the weed killer to the soil, wait the recommended time before planting the new grass.
Weed Killer After the Grass
According to the Garden Counselor, new lawns are no match for weed killers since they do not have the same defenses as older grass. Allow the new grass at least three months before applying a weed killer treatment to the lawn. In that time, the new grass will have more established roots, will have undergone a few mowings and its blades will be thicker and stronger.
It is important to select a weed killer formulated for the type of grass growing in the lawn. Grass-specific weed killers will not damage the lawn as it treats the weeds.
Amongst the best methods of treating a new lawn with weed killer is to apply it in a few light applications than to apply it in one heavily concentrated application. The weeds may respond to a light treatment, and then following it up with one or more treatments may rid the lawn of weeds without stressing the new grass.