Overseeding your lawn is a really important part of having a thicker, healthier and greener lawn with less weeds. It really isn't difficult to do, but it does require some knowledge to get the most germination for your buck. Read on to learn the why, what, how, when and where of overseeding your lawn. Keep in mind, we're a West Michigan-based company, so our recommendations are targeted for this region.
Why should you overseed your lawn? Nature loves diversity. On the flip side, it hates a monoculture. Our efforts, as 21st century American homeowners, to create a monoculture in our lawns goes directly against what nature wants. So, left to its own devices, your lawn is going to have a lot of diversity popping up. You might better know this diversity as "weeds." You don't want weeds (and you don't want to use herbicides)? Put down grass seed and over time, it will push out the weeds.
Now you've got three options when facing the idea of lawn diversity:
1) Let it happen. Just unconditionally accept the diversity popping up in your lawn and love it as you would love a pasture growing wild in the countryside.
2) Drop chemical herbicides onto it. This is how golf courses and baseball fields roll. They put down chemical herbicides to both prevent and kill weeds. It's also how most Americans have been conditioned by the chemical lawn industry to approach their lawns. ("Weeds are BAD!")
Or (our favorite choice) 3) Employ better lawn management practices. This means fertilizing with an organic fertilizer to get richer soil that turf actually wants to grow in. It means watering deeply a couple times a week to encourage deeper roots. It means setting your mower to its highest setting. And it means overseeding your lawn once, and maybe even twice, every single year. The importance of overseeding comes from the fact that weed seeds can find even the smallest gap in your lawn to germinate and establish roots. If you can put down grass seed before the weed seeds can germinate, you'll have grass growing there instead of something you don't want
Now, if you're going to opt for an organic lawn, you're going to have to accept Option 1 to a certain degree. Going organic, you should always expect (and even strive for), at minimum, 10% diversity in your lawn. Anything less than that just isn't healthy. If your lawn is more than 90% grass, you're opening yourself up to pest infestation, fungal infection, higher water bills, etc. But allowing some other stuff (clover, dandelions, violets, etc.) to find a home on your lawn will help keep things balanced and healthy. And telling yourself that some diversity is good for your lawn will even help you relax a bit and enjoy your lawn more, without the stress of striving for perfection weighing you down all summer.
I only recommend Option 2 (chemical herbicides) as a very last resort, and as an organic lawn guy, I don't make specific chemical recommendations. But if your yard has become more than 50% weeds, and you're not happy with how it looks, I'd advise researching ways to start over by killing off what's there, and doing a complete re-seed or re-sod. If you've just got areas that are becoming infested with weeds (creeping charlie, for instance), at the very most, spot treat with an herbicide to kill of the stuff in that area, then re-seed. Again, these are last resorts in my opinion. Pulling up weeds and overseeding is a much more sustainable option
But keeping weeds out isn't the only reason you should overseed. Does your lawn do better in certain parts of your yard than others? Maybe your shady backyard is thick and lush, while your sunny front yard is looking thin and brown during the hot summer months. Maybe the grass under the shade of a tree looks good, while the grass that doesn't receive shade looks terrible. If so, there's a chance your yard was initially seeded or sodded with the wrong type of grass. If a shade-loving grass was put down in an area that never gets shade, it's always going to struggle. Likewise, if a sun-loving grass gets put in a shady area, it's not going to thrive either.
So what's a homeowner to do to fix this sun/shade problem? Overseed with a sun/shade grass seed mix.