Overseeding Weedy Lawn—Waste of Time or Effective?

Anyone who’s had to care for a lawn of their own knows how easily weeds can spread. Once they get into your yard, it’s almost impossible to get them out, no matter the number of herbicides you use. That’s because weeds are opportunistic and will claim any bare or thin patch they can find in your yard. But is overseeding weedy lawn areas a good option? Or will the weeds just crowd out your new grass. I’ll discuss in today’s article.

The best way to get rid of weeds, oddly enough, is to grow a lawn lush enough to kick them out.

If weeds don’t have a place to grow, they’ll stay out of your yard.

One of the best ways to reclaim your yard is to periodically overseed it. Overseeding (or spreading grass seed on an established lawn to help it thicken up) is an effective way to improve your lawn, but it’s no quick fix.

It’ll take a good amount of work, but the results are worth the effort if done correctly.

Let’s talk about effectively overseeding weedy lawn areas and the best times of year to do so.

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How Overseeding Can Help Your Lawn

Overseeding is the method of revitalizing a yard by adding more seed into an existing lawn.

You don’t have to till your lawn, and you don’t have to tear it up for over-seeding a lawn to be effective.

When you overseed new grass grows to fill in the bare spots of your yard, making it grow in greener and thicker.

Overseeding at the right time of year, before weeds are established or after annual weed pressure begins to ease, will ensure success.

How To Succeed When Overseeding Weedy Lawn Areas

The most important things with overseeding are preparation and timing.

You can’t overseed a weedy lawn in the summer when all of your weeds are mature and growing vigorously. You’ll be wasting your time and money if you try that.

For cool season lawns, the best times to overseed your lawn are early spring (when soil temperatures are consistently above 55 degreees Fahrenheit) and early-mid autumn.

The time of year when you overseed your weedy lawn will depend upon why you’re doing it in the first place.

• If your lawn is thin, and you want it to grow in thicker to prevent weeds from growing, early spring may be the right choice to thicken up your lawn without allowing weeds an entire season to thrive. But a word of caution — for spring seeding to be effective you’ll need careful planning, or all that extra love you show to your yard will usher in even more weeds. I recommend that you try a pre-emergent herbicide that is safe for grass seed (most will block your grass seed from germination the same way it blocks weed seeds). I’ve used this product for spring seeding with pretty good results, following up with a selective post-emergent turf herbicide application to clear weeds out once my seed germinates and is mature enough to survive the selective herbicide.
• If you want to give your lawn a hard reset and enjoy the best chance of success, late autumn is the better choice as your new grass will not have to survive the same pressure from annual weeds. It will also allow your spring pre-emergent application and spring fertilization the following year to set your lawn up for long-term success.

The hot summer months are very harsh for new grass seedlings, so springtime isn’t quite as good for most weedy lawns.

Your new grass may not be established enough to survive the heat and drought of summer.

Preparing Your Lawn for Success

Aside from choosing the best time, you must prepare your lawn for overseeding to work the best.

• Cut your grass short. When mowing your lawn normally, you should only cut it by 1/3 its length. But for overseeding, you want the grass short enough to make sure grass seed can get close to the surface. Try cutting the grass by 2/3 its lengths or cut it down to about 1 ½-inches tall.
• Clear your lawn of clippings. After mowing your lawn, make sure there are no clippings on your yard. These can interfere with new grass seed. Either use a bag on your mower or rake them up afterwards.
• Let air into your yard. You want to then loosen up the soil to improve soil contact with the new seeds. This is also a good time to remove thatch from your yard. Either aerate your lawn or use an iron rake to loosen the turf.

Seeding your Lawn

Once these steps are done, it’s time to spread seed onto your yard.

First, choose a grass seed that matches your climate and pairs with your grasses. Also, pick a grass that you can depend on. You want it to grow through the year, and be able to adapt to your yard conditions, like if your yard is sunny or shaded.

I have a guide to choosing the best grass seed for overseeding to help you make the right choice.

Before you begin spreading seed, check the label on the grass seed you purchase for the rate of overseeding. Most bags of grass seed will provide this information right on the bag.

You want to get the right amount of seed in your yard—too much will keep grass from growing because the seedlings compete for moisture, too little and your yard will stay thin and ripe for weed growth.

Once you’ve determined your application rate, use a lawn fertilizer spreader (broadcast spreaders are my preference) to evenly spread it over your yard, and make sure you spread it on a dry day with no wind.

I like to spread some quick-release starter fertilizer on the lawn before spreading my seed. Scott’s makes a really good product (Amazon link), and it’s particularly good for Spring overseeding because it has a crabgrass preventer in the mix.

Spreading a thin (1/4 inch) layer of compost over the new seed will work wonders to improve germination and help your new seedlings thrive.

You’ll probably want to review my guide to watering new grass to improve your results.

Maintaining Your New Grass

Watering your new grass is critical and knowing the stages of watering is very important.

New grass needs a lot of water, and you want your soil to stay constantly moist.

For new grass, water lightly twice per day for the first week, and water more heavily the second week.

After 2 weeks, water heavily and less frequently. You want the soil saturated down to 6-inches each time you water it past the 2 week point. This will encourage your grass seedlings to grow deep roots which will improve your lawn’s resilience to heat and drought.

Wait several weeks before mowing your lawn.

Make sure the grass is over 3 inches (I recommend 4-inches in height for the first mow), otherwise you risk ripping your seedlings out of the turf because their roots won’t be deep enough yet.

When you do mow, bag your grass clippings the first few times, and adjust your mowing deck to cut no more than 1/3 of the grass blade.

Similarly avoid herbicides for several weeks on new grass.

If you used starter fertilizer, I recommend throwing down organic slow-release fertilizer after 4-6 weeks to sustain and feed your new lawn and keep it healthy.

Annually overseeding weedy lawn areas in combination with the use of pre-emergents every spring will gradually transform your weedy yard into the lush green carpet every homeowner wants.