If you have had a dry summer with below-normal rainfall, you need to replenish soil moisture before preparing a seedbed. Give the entire lawn a thorough watering, soaking until water has penetrated to a depth of at least 6 inches, then allow the surface to dry for a day or two before starting soil preparation.
The soil nutrients most important to healthy grass plants are nitrogen, potassium and phosphorous. Supply these nutrients by applying a commercial fertilizer formulated for starting lawns and lightly rake it into the soil before you reseed. Buy a grass-seed blend suited to your climate and local conditions and spread it over the lawn with a drop spreader or rotary spreader. Absent a different recommendation from the grass-seed grower, spread the seed at a rate of 2 pounds per 1,000 square feet on a lawn with substantial plots of live grass and 3 pounds per 1,000 square feet on bare soil. Water lightly once or twice a day to keep soil moist but not sopping wet. Don’t mow until the new grass gets 3.5 inches tall.
Water the Site
Most deteriorated lawns have a built-up layer of dead and partially rotted grass stems, roots and rhizomes just below the green grass leaves. This is known as thatch, and it must be removed before reseeding so water and fertilizer can reach the new seed. For small lawns, you can remove thatch with a garden rake. For large areas, go over the lawn with a power dethatcher, also known as a vertical mower or power rake. These machines can be rented from garden centers. Remove the clumps of matter left by the machine with a garden rake and level the soil by raking it.
If you are faced with a neglected lawn that’s partially dead and is being taken over by weeds, you may be able to renovate it. Restoring a deteriorated lawn may be possible if the weeds and dead spots cover less than 40 percent of the lawn area. Renovation of a weedy lawn involves more than just mowing down the weeds and throwing some grass seed over the lawn.
The best time for lawn renovation throughout the U.S. is mid-August to mid-September. Most weeds have not yet dropped their seeds and there will be little new weed growth. Also, reseeding at this time will give the new grass a chance to establish itself before going dormant for winter. Get rid of the weeds by manually pulling up large, spreading weeds. Follow up by applying a selective herbicide product that kills common broadleaf lawn weeds while not harming grass. For tough grassy weeds, like quack grass or crabgrass, use a nonselective herbicide such as glyphosate on the spots where these weeds have established themselves. Normally, all weeds will be dead within two weeks. Apply another herbicide dose in three weeks to get newly sprouted weeds.
Till the top 6 inches of soil with a soil tiller. You can rent or purchase soil tillers at home improvement centers and rental yards. After the tiller turns under the dead weeds and soil, rake the soil with a garden rake to level the area as much as possible. Remove large rocks and break up clumps of soil.
Apply a thin layer – about 1/4 inch – of high-quality topsoil over the grass seed. Applying too thick and the seeds have a hard time germinating. Attach a garden hose sprayer with a mist option to a water hose. Dampen the top 6 inches of the soil with the water hose set on mist. Using a mist of water instead of a stream will prevent the seeds from washing away.
Cover the soil with the correct grass seed for your location and the amount needed to cover the area. For example, some parts of the San Francisco Bay area work best with warm-season grasses — such as St. Augustine, buffalo or zoysia grass — while other Bay areas thrive with cool-season grasses such as tall fescue and perennial rye. Use your gloved hands to distribute the seeds evenly over areas smaller than 150 square feet. For larger areas, use a seed spreader.
Trying to grow grass in a weeded area is a frustrating task that generally provides undesirable results. Weeds are aggressive and invasive plants that choke out grass and flowers. They quickly take over an area and are notoriously hard to get rid of. When you choose to grow grass in an area overrun by weeds, you essentially have to start fresh by establishing new turf.
Remove the weeds from the area by either manually pulling them out of the ground or applying weed killer to the area. Hand-pulling weeds is safer for the soil, but removing all the roots can be difficult. Chemical weed killer kills the weeds and their roots, but may damage grass seed and leave pesticide residue in the soil, if you plant the seeds too soon after the herbicide application. If you choose to use weed killer, wait 2 to 3 weeks before planting new grass seed.
Keep in mind that herbicides can kill whatever plant life they come into contact with—even if the label says otherwise—so handle with care. If your aim is to re-establish your lawn, as we recommend, killing your existing, thinning grass isn’t a big deal, since you will need to start fresh anyway.
Deep, infrequent watering can help establish your lawn by allowing it to grow deep roots, which can compete against weeds. Try to water your lawn about twice a week, in the morning before the heat of the day sets in. Lawns typically need about 1.5 inches of water per week, but that could vary based on the climate you live in and the type of grass seed you chose.
If you only have a few pesky weeds punctuating your lawn, you may be able to dig them up by hand—paying careful attention to make sure you get them roots and all. But if your lawn is overrun with weeds, you may need to start from scratch. Here’s our how-to guide on restoring a lawn full of weeds.
Top the seed with top dressing no greater than ¼ inch thick.
Next, it’s time to select the proper weed treatment based on both weed classification and the stage in their life cycle. Pre-emergent herbicides tackle weed issues before they spring up. Post-emergent herbicides target established weeds.