Seeding on top of weeda

Will Overseeding Choke Out Weeds?

Overseeding your lawn will thicken the grass, helping it resist future weed invasion. However, it is best used on a lawn where the weeds are currently dormant or have recently been killed. Spreading grass seed on a weedy lawn won’t do much good. Weeds that are actively growing in your grass will steal water and nutrients from grass seedlings, causing them to struggle and die. For best results, attack lawn weeds with a weed killer, then overseed to create a healthy lawn that prevents weeds from returning.

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How Does Overseeding Help Prevent Weeds?

Overseeding your existing lawn with new grass seed fills in bare spots and contributes to thicker grass throughout the lawn. A thick grass lawn without bare spots shades the soil below, depriving weed seedlings of sunlight, killing them. Not only that, but thick growing grass pulls moisture and nutrients from the soil first, before weed seedlings can get to them.

  • Overseeding contributes to a thicker lawn.
  • Bare spots that have been overseeded with grass are less prone to weed invasion.
  • Lawns thickened by overseeding prevent weed seedlings from receiving sunlight and nutrients, smothering them.
  • Regular overseeding maintains a thick, weed-resistant lawn without herbicides.

Grass plants, like all plants, weaken and die naturally over time. By overseeding you replenish your lawn with new grass plants. This constant replenishment keeps your entire lawn thick enough that it continues to smother new weeds. This reduces the need to use chemical weed killers on your lawn.

Do You Need to Remove Weeds Before Overseeding?

Overseeding is most effective when you kill existing weeds before you overseed. This is because grass can’t choke out existing, established weeds no matter how thick it is. A lush lawn can only stop new weed seeds from sprouting. Also, any weeds that are present when you overseed will steal water, nutrients, and sunshine from your new grass seedlings. Wipe out the weeds to give your grass a fighting chance.

  • Remove existing weeds before you overseed.
  • Existing weeds won’t be killed or choked out by overseeding. A thick, overseeded lawn will only suppress new weed growth.
  • Kill established weeds or they will rob water and nutrients from your grass seedlings.

You’ll get more new grass sprouts from overseeding if you kill existing weeds first. Overseeding a lawn overgrown with weeds will get a poor yield. Your new grass will struggle to compete with the weeds. Paving the way for new grass by killing weeds is your best bet.

What is the Best Time of Year to Overseed a Weedy Lawn?

For the best results overseeding your lawn, you need to seed at the optimal time for your grass type. Warm-season grass lawns (such as Bermuda, Zoysia, and Centipede grass) should be overseeded in spring. Cool-season grasses (Kentucky Bluegrass, Fescue, Ryegrass) sprout and survive best when overseeded in fall.

  • Overseed warm-season grasses in spring.
  • Overseed cool-season grasses in fall.
  • It’s best to overseed when no weeds are present.

Another factor that makes overseeding in fall a great option for cool-season grass lawns is that few weeds will be present. Even if your lawn was infested with crabgrass in spring, by fall it will have begun to drop its seeds and die off. If you overseed in fall, your new grass will sprout and establish itself. By spring, the grass will be thick enough to prevent many of those crabgrass seeds from sprouting.

What is the Best Grass Seed to Use for Overseeding?

The best grass seed for overseeding is grass that will grow well in your climate. In regions with freezing winters, choose cool-season grass. In regions where winters seldom freeze, warm-season grass will perform best.

  • Seed with cool-season grass in regions with freezing winters.
  • In regions with mild winters, overseed with warm-season grass.
  • Match your grass seed to the variety of grass present in your lawn.

It’s also important to note that overseeding is the act of spreading additional grass seed over an existing lawn. It’s usually best to overseed your lawn with the same species of grass that is present there. This will create a uniform, beautiful lawn.

What Grass Will Choke Out Weeds?

The best grasses for choking out weeds in your lawn depend on your location. If you are planting warm season grass and wish to have a weed-resistant lawn, Bermuda grass is your best choice. It spreads through runners and roots to take over areas, which prevents weeds from getting a toehold.

  • Bermuda grass is the best warm-season grass for choking out weeds.
  • Kentucky Bluegrass is the top option for battling weeds in cool-season grass lawns.

Kentucky Bluegrass spreads faster than any other cool-season grass. It produces roots that form new plants in both spring and fall, meaning it self-thickens and fills in bare spots. If you want to weedproof your northern lawn, go with KBG.

Will Overseeding Your Lawn Get Rid of Weeds?

Overseeding a weedy lawn will not kill weeds on its own. However, thick grass growth produced by overseeding prevents new weeds from sprouting. In order to keep your lawn weed-free with overseeding, first, kill any existing weeds, then prep your lawn and spread new grass seed. The thick growth of new grass will choke out new weed seedlings as they attempt to sprout.

How to Grow Grass in a Weeded Area

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.

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.

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.

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.

Continue watering the soil two to three times a day until the seeds have germinated and the grass is about 1/2-inch high. After germination occurs, you can cut back watering to once every day or two. Never let the seeds dry out.

How to Reseed a Lawn With Weeds

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.

Kill the Weeds

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.

Water the Site

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.

Remove Thatch

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.

Feed & Seed

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.

  • University of Minnesota Extension: Lawn Renovation
  • Southern States Cooperative: Reseeding Your Existing Lawn

Herb Kirchhoff has more than three decades of hands-on experience as an avid garden hobbyist and home handyman. Since retiring from the news business in 2008, Kirchhoff takes care of a 12-acre rural Michigan lakefront property and applies his experience to his vegetable and flower gardens and home repair and renovation projects.