Will Overseeding Get Rid of Weeds in Your Lawn?

A lush green, weed-free lawn is the dream for many homeowners. But achieving this can be difficult especially if your lawn already has a lot of weeds. So when it comes time to reseed and thicken up your lawn, a common question is whether overseeding will also get rid of the weeds.

The short answer is no – overseeding alone will not get rid of existing weeds However, it can be an important part of an integrated strategy to control weeds and improve the health and thickness of your lawn over time

What is Overseeding?

Overseeding is the process of adding new grass seed over your existing lawn. The goals are to fill in bare or thinning spots, increase turf density, improve color, and crowd out future weed growth.

It involves sowing grass seed directly on the soil surface without tearing up or removing the current grass. The seed then germinates and grows new grass plants that integrate into the existing turf.

Overseeding is typically done in early fall when conditions are ideal for cool season grass seed germination and growth. But it can also be done in spring or summer as needed to address problem areas.

Will Overseeding Eliminate Existing Weeds?

Unfortunately, simply spreading new grass seed over the top of weeds will not get rid of those mature weeds that are already established. Any living weeds will remain and compete with the new grass plants unless removed prior to overseeding.

There are a couple reasons overseeding itself does not control existing weeds:

• It does not affect mature plants – Overseeding introduces new grass into your lawn, but does not directly impact mature weeds that are already growing. The new grass seeds germinate and grow up around existing weeds.

• No selective control – Grass seed spreads indiscriminately across your lawn. Unlike selective herbicides that target specific weeds, overseeding does not differentiate between desirable grass and weeds.

• Life cycle differences – Annual weeds that sprouted from seed tend to die off when the weather turns cold in fall. But perennial and biennial weeds continue living and competing with young grass plants.

For these reasons, overseeding alone does not provide effective weed control in an established lawn. Removing weeds beforehand is key to prevent competition and give new grass the space it needs to thrive.

How Overseeding Helps Control Future Weeds

While overseeding does not kill existing weeds, it can help reduce weed problems going forward. Here’s how:

• Thickens turf – Overseeding improves turf density, filling in thin and bare areas that are vulnerable to weed invasions. This gives grass the advantage in limiting weed seed germination.

• Improves turf health – Addressing factors that weaken grass plants, like improper mowing, disease, poor drainage, or nutrient deficiencies, enables the lawn to better outcompete weeds. Overseeding is one strategy to strengthen your turf.

• Reduces room for weeds – The more space is taken up by dense, healthy grass plants, the less room there is for weeds to establish. Overseeding adds more desirable grass to crowd out and choke future weed growth.

• Outcompetes weeds – Vigorous young grass plants from fresh seed can better compete with weed seedlings. As new grass matures, it’s better able to win resources and keep weeds at bay.

So while overseeding alone won’t eliminate existing weeds, following up with proper lawn care and maintenance gives your new grass the upper hand against future weed invasions.

How to Overseed a Lawn with Weeds

The best practice is to remove weeds prior to overseeding whenever possible. Here is a step-by-step process for overseeding a lawn with weeds:

1. Kill Existing Weeds

• Apply a non-selective herbicide like glyphosate in early fall to kill all vegetation. This bare earth approach allows new grass to grow without competition. Wait 1-2 weeks for complete weed death before overseeding.

• Spot treat weeds with a selective post-emergent herbicide like 2,4-D or dicamba at least 2-3 weeks before overseeding. This leaves desirable grass in place while removing broadleaf weeds prior to seeding.

• Manually hand pull small weed patches. This works best for annual weeds with shallow roots.

2. Mow Low

• Scalp the lawn down to 1-2 inches using a rotary or reel mower. This helps with seed-to-soil contact for better germination rates.

• Bag clippings to remove debris that could impede seedling growth. Mowing low also further weakens existing weeds.

3. Dethatch and Aerate

• Dethatching removes thick layers of accumulated debris that block seed from reaching the soil.

• Core aeration punches holes through thatch and compacts soil, allowing better water and oxygen infiltration.

4. Spread Seed

• Use a spreader to distribute grass seed evenly across bare or thin areas of the lawn. Apply at recommended overseeding rates.

• Consider a starter fertilizer to provide nutrients for establishment. Look for formulas safe for new seeds.

5. Water and Wait

• Water lightly and frequently, keeping seeds moist for germination. Once sprouted, reduce watering frequency.

• Let new grass establish deeper roots and thicken for 4-6 weeks before resuming normal mowing, feeding and weed control.

Proper lawn maintenance is key following overseeding. Control any new weed growth while nurturing newly seeded areas as they mature. Overseeding coupled with vigilant weed management provides the one-two punch needed to cultivate a lush, green lawn.

FAQs About Overseeding Lawns With Weeds

Should I kill weeds before overseeding a lawn?

Yes, removing existing weeds prior to overseeding is strongly recommended. This prevents competition that can smother or stunt young grass seedlings. Kill weeds 2-3 weeks before overseeding using selective herbicides or non-selective products for complete vegetation control.

When is the best time to overseed a weedy lawn?

The optimal time is early fall when temperatures cool, rainfall increases, and weed pressure drops. Overseed when daytime highs reach 70-75°F to allow 4-6 weeks of growth before winter dormancy. Late summer overseeding works too in warmer regions.

What’s the best way to get rid of weeds when overseeding?

Non-selective herbicides that kill all vegetation provide the most effective weed control prior to overseeding bare spots or renovating an entire lawn. Glyphosate products can be sprayed 1-2 weeks before seeding for clean slate results.

Should I dethatch or aerate before overseeding weeds?

Yes, dethatching and aerating help facilitate good seed-to-soil contact and reduce weed competition. Dethatching removes layers of debris that prevent seedling growth. Aerating opens up the soil for better establishment.

Can I overseed without killing weeds first?

While not ideal, overseeding without removing weeds is possible. Mow very low, rake vigorously, and seed heavily to compensate for weed pressure. Accept some weed growth along with new grass. Spot treat weeds or use selective pre-emergent herbicides after establishing.

How soon can I treat weeds after overseeding new grass?

Wait 4-6 weeks after overseeding to allow young grass plants to mature before applying herbicides. Selective post-emergent products can then be used to control broadleaf weeds. Avoid weed-and-feed fertilizers until the grass has gone through two mowings.

Overseeding is a great way to improve the density, thickness, and health of your lawn when done properly. While overseeding alone will not eliminate existing weeds, controlling weeds prior to seeding and maintaining vigorously growing grass after is key to limiting weed problems long-term.