Aerating vs Dethatching When Overseeding

Good seed to soil contact is about as important as watering grass seed to get good germination rates when overseeding. Core aerating and dethatching are both recommended practices when you plant to overseed. But is it better to aerate or dethatch when overseeding?

I've done both in the past and in my opinion, dethatching will give you better results. This post contains my recommendations for dethatching and overseeding.

Core aeration will help if you have compacted soil and will get more water and nutrients down into the soil to help encourage deeper root growth. But it doesn't expose much soil. A rate of 16 holes per square foot is a normal aeration rate. The holes are only 1/2" in diameter and at that rate you're only creating holes in about 2% of the lawn. If you leave the plugs on top of the lawn instead of raking them up, you'll get a little bit of soil exposed there too but it's not a great place to germinate seeds. It only increases the percent of exposed soil slightly sits on top of a layer of thatch and dry out quickly.

When the grass seeds start to germinate in the holes, there is also the possibility that they get choked off when the soil starts to fill in.

Dethatching on the other hand will expose more soil by removing the thatch layer. The tines of the dethatcher also cultivate the soil giving it a nice tilth which will help the seeds embed in the soil rather than just lay on top. This is similar to raking your vegetable garden to loosen the soil before planting seeds.

The dethather also helps groom the grass roots close to the surface. This will give the new roots more room to grow.

Another benefit is that using the thatch rake helps me find crab grass and other prostrate grassy weeds. Because of the prostrate growth, the stems/blades are longer than grass. When I rake them the longer blades are easier to spot. It's hard to describe but you'll know it when you see it. When you come across these weeds, just keep your Weed Hound and remove it.

Dethatchers

I don't have a very large lawn area and I also prefer when I can to ise manual tools like the thatch rake pictured right. Being "green" seems to go hand in hand with organic gardening and lawn care but that's not the reason I do it. I just think it's good cardiovascular exercise. It also works out your arms, back chest, legs and core. Sometimes when I'm dethatching I'll count each stroke (in my head so people don't think I have OCD) and then switch hand positions on the rake every couple of dozen strokes but usually I lose track if I have to stop to pull a weed and just try to switch as evenly as I can.

Otherwise you can rent a dethatcher, sometimes called a power rake, buy a Dethatcher Attachment if you have a Mantis Tiller or a tow behind dethatcher if you have a riding mower.

Overseeding

Once the dethatching is done, remove the thatch and place it in your compost pile if you have one. Then spread a good quality grass seed. Galaxy Kentucky Bluegrass Blend is a good choice for many sunny areas here in the northeast. If you have shady areas review my shade grass seed recommendations.

After the seed is down a topdressing of 1 yard of compost for every 1,000 sq ft is recommended. It will help keep the seeds moist, provide nutrients... just improve germination in general. The compost will also add organic matter to the soil. In between seeding and topdressing you can go over the seed with the back of a rake, use a roller or find some other method to help get the seed down into the soil. I don't have a roller, I'm not sure a rake works that well when overseeding so I just water the lawn for a few minutes to wash the seed down into the soil. Then water it in again after applying the compost.

If you have really fine compost that doesn't have a high moisture content, you can sometimes spread it with your spreader. If that's not working out I like to just grab a small bucket full and sprinkle it over the lawn. It's slower than pushing it around with a rake but it won't disturb the seed as much either.

This should give you very good results so you can fill in thin or bare areas in your lawn.