Overseeding a Weedy Lawn – Does it Work and Should You Do It?

Your lawn is overrun with weeds and you’re wondering what to do about it.

You’ve heard about overseeding but you’re skeptical. And that’s fair enough!

No one wants to waste a bunch of seed, time and effort if it might not work, right?

I’m going to tell you a bit more about overseeding a lawn with weeds, whether it works and how to do it if you decide that it’s right for you.

Let’s get into it!

Key Points

What is Overseeding?

Overseeding is the practice of adding seed to an already established lawn, but one that has a few too many bare patches and/or weeds present.

Usually, you will also add a layer of compost and fertilizer at the same time to give the seeds the best possible shot.

Does Overseeding a Weedy Lawn Work?

Yes!

Overseeding a lawn with weeds does work, but there are some caveats to this. Some lawns will respond better to overseeding than others, and there are right and wrong ways to go about overseeding a weedy lawn.

It helps to understand a little about why lawns get weedy in the first place and how overseeding helps.

All plants, including both grass and weed species, need space and light to survive. A healthy lawn will be so lush and dense with the grass species that you want, that there won’t be much opportunity for weeds to arrive and establish themselves.

But, as soon as your lawn gets a little overgrown and/or bald spots appear, any weeds that might be present get an opportunity to go to seed, and any seeds arriving on the wind have an easier time finding space to get established.

What does this mean for us?

So, with this in mind, you might be wondering, will overseeding kill weeds?

Overseeding a weedy lawn doesn’t directly kill the weeds that are already present. But, if done at the right time of year, the growth of enough healthy grass will outcompete the weeds by starving them of light, space and water, and prevent more weeds from growing.

Exceptions to the Rule

While re-seeding a moderately weedy lawn with bare patches works really well most of the time, there are some weeds that are so stubborn and relentless that outcompeting probably won’t work.

A good example is crabgrass. You may have to apply some other management tactics to control your crabgrass if you have a lot of it. Luckily, there are natural ways to manage crabgrass that are a lot safer, and sometimes more effective, than relying on herbicides.

Other weeds that may require some specific attention are dollar weed and Bermuda grass (in some parts of the world, Bermuda grass is the lawn species of choice, but if its growing where you don’t want it to then it becomes a weed).

When Should I Overseed my Lawn?

The timing of overseeding can be the deciding factor in how successful it is.

Both grass and weed species have a period of the year where they are dormant and periods where they are growing.

The trick is to time your overseeding project for when grass growth is at its peak and most weed species are dormant. This may not always be completely possible as there will be some overlap, but some times of the year are definitely more optimum than others.

For most regions, late summer or early spring are the best times. However, if you have applied any non-organic fertilizers or selective herbicides designed to prevent seed germination, you’ll need to wait a while until those chemicals are no longer present.

Tips for Successfully Overseeding Your Lawn

Carry Out Some Prep Work

Rather than just jumping in and overseeding straight away. Taking a few steps beforehand can make your overseeding much more successful.

Hand pulling any really large and obvious weeds is probably a no-brainer but worth mentioning all the same. You want to create conditions that will maximize the chances of the grass seed being more successful than the weeds. So, give it a fighting chance by removing what weeds you can first.

Giving your lawn a good watering (enough to reach 6 or so inches down into the soil) a couple of days before overseeding is also good practice. If you water too much immediately after overseeding you may just drown the seeds.

Mowing your lawn really short before overseeding also gives the new seeds a good chance of success without being shaded out by existing grass. But be sure to remove the grass clippings. While leaving a fine sprinkling of grass clippings is a good practice most of the time (read this article to find out why), you don’t want any grass clippings on your lawn before overseeding.

Removing thatch is important for similar reasons. New seeds won’t have much of a chance if they have to fight through thatch first. If you’re new to dethatching, I have a how-to guide here.

Choose the Right Grass Seed

Did you know that there are many different species of grass that can make up a lawn seed mix? The species you choose will play a large role in how successful your overseeding project is.

You can also exercise some preferences depending on whether you want thin or thick blades of grass, hard-wearing for lots of foot traffic or less hard-wearing but more aesthetically pleasing, and low maintenance that doesn’t need mowing as often, or faster-growing that does require regular mowing.

In saying that, if you already have some grass seed left over, then by all means use it. There is no sense in letting it go to waste. Chances are it will still be fine to use as well. If you’re not sure, I’ve explained how to work out if grass seed is bad in this article.

How to Overseed

Last but not least, let’s explore how to actually reseed a lawn with weeds.

Assuming you’ve carried out the preparatory steps above, the main steps to overseeding are spreading compost and fertilizer, spreading the seeds, and then watering.

Applying around ½ ich of compost over your lawn will provide an easy growing medium for your seed to germinate in. There’s a chance you may have some success without doing this but your germination rate will be much lower.

Applying your own homemade compost is an excellent choice here as you can save money and you know exactly what you’re putting on your garden which is a must if you have kids and pets.

It’s also helpful to fertilize in order to make sure that all of the nutrients required for healthy grass growth are present. Organic fertilizers are superior in the long run when it comes to soil health but a one-off application of synthetic fertilizer when you overseed is not going to do any major harm.

If you’d like to learn more about the world of fertilizer,  I have some helpful articles on when and how often to fertilize, the difference between liquid and granular fertilizer, and the shelf life of different kinds of fertilizer.

The next step is to sprinkle a fine layer of seeds over your lawn. You want around 15-20 seeds per square inch and this can be made easier with the right equipment. A handheld broadcast spreader is best for regular size lawns but if you have a big area to reseed, you might choose a tow behind spreader instead.

After applying the seed, rake it into the compost a little bit and ensure its evenly spread.

Finally, give your thirsty lawn a drink with a sprinkler (or some of your own harvested rainwater if you’ve got your collection tanks set up), and then wait for the magic!

Summary

Hopefully, you’re feeling pretty knowledgeable when it comes to the ins and outs of overseeding lawn with weeds.

It’s actually not super complicated and it’s definitely the best solution to managing a weedy lawn. Simply get the timing right and with the right seed, your lawn should be well on its way to being lush and weed-free.

Have you tried overseeding a weedy lawn? What did you do and did it work? I’d love to hear how it went for you!

Also, if you are interested in taking the best care of your lawn, take a look at our take on the different types of lawn movers, so you can take the next step in improving your lawn after the weeds are taken care of.