Weeds are opportunistic plants that will take over your lawn if you give them the chance to. If your lawn is thin or has bare spots, it won’t be long before those areas are taken over by weeds during the growing season.
Although it can’t be used to beat established weeds, overseeding is an effective natural method of weed prevention if carried out at the right time of year. The new grass will help your lawn to outcompete the weeds early in the growing season, leaving you with a thick, healthy, weed-free lawn all year round.
What is Overseeding?
Overseeding is the process of adding new grass seed to an existing lawn. This practice allows you to revitalize your current lawn without having to till it or tear it up. It gives you the opportunity to fill in your lawn with a new turfgrass variety using relatively little effort.
By overseeding your lawn, you can improve turf density, fill in bare spots, and enhance the overall appearance and color of your grass. An overseeded lawn is more resistant to the stress brought about by pests, disease, drought, and foot traffic; in turn, this reduces the amount of fertilizer, water, and pesticides that you have to use on your grass. On top of this, overseeding is an easy way to choke out and prevent the growth of weeds.
How Does Overseeding Prevent Weed Growth?
When you overseed effectively, the grass seed fills in bare spots of soil on your lawn with new growth. This eventually leaves you with a lawn full of thicker, healthier grass. As a result, the thick growth provides the soil surface with better shade from the sun.
Without access to sunlight, weed seeds on the soil surface are unable to germinate and grow into seedlings. A thicker lawn also smothers any young weed seedlings by limiting their access to the sun. Furthermore, the new grass growth pulls water and nutrients from the soil before the weed seedlings have a chance to. This helps to prevent the growth of grassy weeds, such as crabgrass or nutsedge, and broadleaf weeds like clover or spurge.
Should You Remove Established Weeds Before Overseeding
Yes, it’s advisable to remove the existing weeds on your lawn to maximize the effectiveness of your overseeding. While thick grass can choke out young weed seedlings, it won’t be able to do the same for established, mature weeds. As we’ve explained, overseeding blocks the sun from reaching weed seeds on the soil surface. This is enough to stifle the weeds before they germinate, however, it won’t be enough to kill fully-established weeds.
Also, if you attempt to overseed your lawn when it’s already full of weeds, it could impact the growth of your new grass seed. The established weeds will steal vital nutrients, water, and sunlight from your new seedlings, hindering their germination and growth. The grass will struggle to compete with the weeds and this will result in a lower overall yield; in other words, less of the new grass seedlings will successfully grow into established grass plants.
Note: If you have a lawn full of weeds and decide to use a weed killer, you will need to wait a period of time before attempting to overseed. How long you should wait will depend on the specific type of weed killer you’re using. Refer to the guidance on the packaging for your chosen product to find out how much time you should leave between its application and overseeding your lawn; this will typically be about 6 weeks after the application of the weed killer.
What is the Best Grass for Overseeding a Weedy Lawn?
The best grass for overseeding your weedy lawn will depend on the region that you live in. You must choose a grass type that is compatible with your local climate and the established grass already on your lawn. This ensures that your new grass will thrive and blend well with your already-established grass.
Best Grass to Overseed a Northern Lawn
If you live in a cool northern region that experiences harsh freezing winters, cool-season grasses are your best choice. The best cool-season grass to overseed a weedy lawn is Kentucky Bluegrass.
Kentucky Bluegrass is the fastest-spreading cool-season grass type, making it an ideal grass to battle weed growth. This grass species self-thickens and fills bare spots by producing roots that form new grass plants in both the spring and fall.
Best Grass to Overseed a Southern Lawn
If you live in a southerly region that sees mild winters, you’ll get the best results from overseeding with warm-season grass. The best warm-season grass to overseed a weedy lawn is Bermuda grass.
Bermuda grass takes over bare areas of soil by spreading through runners and roots. This prevents the germination of weed seeds and seedlings by choking them out with healthy grass growth.
When to Overseed Weedy Lawn
As is the case when planting grass under any circumstances, the best time to overseed depends on the grass species. You will first need to identify the type of grass seed you’re planting; i.e., you must establish whether you’re planting a cool-season or warm-season grass.
When to Overseed Cool-Season Grasses
Overseed cool-season grasses in the fall. At this time of year, the soil temperatures are still warm enough from the summer to trigger seed germination. This also gives the seed a chance to become established before the winter frost sets in. Planting cool-season grass in the fall is one method you can use to keep your grass green in winter.
Cool-season grasses include Kentucky Bluegrass, Fescue, and Ryegrass. These grasses are typically found in the cool more northern regions of the US.
When to Overseed Warm-Season Grasses
Overseed warm-season grass types in the spring. At this time of year, soil temperatures are warm enough for the seeds to germinate before it gets too warm in summer.
Warm-season grasses include Bermudagrass, Zoysiagrass, and Centipede grass. These grasses are found in the warmer southern regions of the US.
How to Overseed Weedy Lawn
Follow these steps to effectively overseed your lawn and prevent the spread of weeds.
1. Remove Established Weeds
If your lawn already contains established weed growth, you will need to remove the weeds before attempting to overseed. As we’ve explained, your new grass seedlings will have a hard time outcompeting already-established weeds. Neglecting to remove the weeds before overseeding will likely result in a low yield from your overseeding efforts.
Removing Weeds By Hand: The best way to remove weeds before overseeding is to do so manually, by hand or using a weed puller. First, water the lawn to soften the soil. Then use your hands or weed puller to pull up as much of the visible weed growth as possible. Dispose of the weeds somewhere far away from your yard; avoid placing them onto any compost heaps, otherwise you risk reintroducing them back into your yard when you use the compost.
Removing Weeds with Weed Killer: Although it’s less advisable to use a chemical weed killer before overseeding, you can opt for this if you prefer. Timing is crucial with this method of weed removal; you need to leave enough time between applying the weed killer and overseeding to prevent killing your new seedlings. Your chosen herbicide will come with an indicated waiting period on its packaging to help you with this timing.
2. Mow Lawn as Short as Possible
The next step is to mow the lawn as short as possible, a practice also known as scalping the lawn. By cutting the grass short, you improve the seed-to-soil contact of the new grass seed. This in turn improves the overall germination rate of the seed.
Method: Adjust the height of your mower deck to the lowest possible setting. If you have a level lawn, you can set the deck height to as low as 1 inch from the ground. If not, setting the blades closer to 2 inches will help protect your mower blades from getting damaged. When you’ve adjusted the deck, mow the lawn as you usually would. Use a bagging attachment if your lawn has weeds gone to seed to avoid spreading them further around your yard.
3. Remove Grass Clippings and Debris
After you’ve mowed, remove the grass clippings and all other organic debris from your lawn. If this matter is left on the lawn, it can block the grass seed from making contact with the soil. Raking the debris helps to loosen up the topsoil, putting it in better condition for the new seed. Also, this gives you the opportunity to remove any moss that’s growing in the thatch layer of your lawn.
Method: Use a heavy-duty rake to rake up any grass clippings or other organic matter from your lawn. Bag and dispose of the grass clippings or use them for other purposes around your home.
4. Dethatch Lawn
You will also need to remove any thick layers of thatch to improve seed-to-soil contact. Thatch is the layer of tangled organic matter that sits between the soil surface and the upper grass growth; this layer will be particularly noticeable if you have mowed lower than usual following the previous step.
Method: Dethatch the lawn using a dethatcher or power rake. It’s also possible to dethatch using a rake. Use your tool of choice to break down the thatch layer before collecting, bagging, and disposing of the debris.
5. Aerate Lawn
Lawn aeration is another highly beneficial practice to carry out before sowing new grass seed, especially when overseeding. This is the process of creating small holes throughout the soil in your lawn, either using a spike or core aerating tool. These holes allow air, water, and nutrients to pass easily through the soil to the grass plants’ root zone.
Aeration helps improve the soil’s overall planting condition by breaking up areas of compaction. It also allows better seed-to-soil contact when overseeding, as well as providing better protection for the seeds from adverse weather conditions and hungry birds. This is a much better option than simply sprinkling the seed and hoping for the best.
Method: After removing weeds, mowing, and dethatching the lawn, use a spike or core aerator to aerate the soil. If using a core aerator, leave the soil plugs on the lawn; they will enrich the soil as they gradually break down over time.
6. Sow New Grass Seed
Now that your lawn is fully prepped, you can begin the overseeding process and start sowing your new grass seed. It’s best to use a broadcast spreader for this to ensure the seed is spread as evenly across the lawn as possible.
The rate at which you sow the seed will depend on the specific recommendations for your grass type. Follow these recommendations to get the best chances of thick, full growth when the new seedlings grow in.
Method: Set your broadcast spreader to the right settings for your grass type. Begin by planting half of the seeds by walking the spreader in rows across your lawn. After you’ve covered the lawn, sow the second half of the seed in rows perpendicular to the first pass.
7. Gently Rake New Grass Seed
When you’ve finished sowing the seed, you should then gently rake it into the soil. This helps to further improve seed-to-soil contact, increasing the seeds’ chances of successful germination. Skipping this step means that a lot of your seed won’t be making sufficient contact with the soil to germinate. The seeds will also be more susceptible to being washed away or eaten by birds if you neglect this step.
Method: Use a rake to gently work the seed into the soil on your lawn.
8. Water Lawn
Finally, you should give the lawn a light watering to provide the new seeds with enough moisture to trigger germination. Avoid adding too much water or using a heavy sprinkler system as this will wash away your newly sown seed from the planting area.