On a busy year, I have put off seeding my lawn for so long that time simply ran out. I could aerate, but the forecast called for snow just a week later. It was mid-November and winter was here. Still, I aerated the ground and, a few days later, I overseeded it. A few months later, when the weather began to warm up, I could tell that the thin patches in my lawn were filling in and the seeds had braved the cold to thrive this spring. This isn’t always how it works. Knowing when it’s too late to aerate and overseed your lawn in your climate, is key to keeping your lawn healthy and lush.
When Is It Too Late to Aerate and Overseed – The Short Answer
It’s too late to aerate if the ground is frozen and it’s too late to overseed if there is snow on the ground. If you want to do both of these at the same time, you need unfrozen ground. If you want your seeds to germinate in the same year you plant them and you want those seedlings to survive and later thrive, you need about 4 weeks of temperatures above 50F. However, you can also aerate and overseed in the fall and have those seeds germinate in the spring.
How to Tell If It’s Too Late to Aerate and Overseed
Temperate, time of year, and water levels are all things to keep an eye on if you want to overseed in the fall. Below you can learn why and if there are any exceptions to these rules.
There are Consistent Freezing Temperatures (Winter)
Is it too late to aerate and overseed if you’re seeing temperatures consistently below 32F? Yes. Now the ground is too hard to aerate. If other conditions are right, you could, however, still get by using an overseeding method that allows for a period of extended dormancy.
It’s October or November
Is November too late to aerate and overseed a lawn? Not always. The general rule in Zones 4 to 6 is that the end of October means heavy frost followed by a freezing winter. In Zone 7, this is extended to the end of November. This accounts for the majority of the US. While a good quick rule of thumb, there are situations where overseeding and aeration can still be safely done during October or November in these regions.
Your Yard is Flooded
Standing water before winter is never fun to deal with. It also makes it so you shouldn’t aerate or seed your yard. A wet fall followed immediately by freezing temperatures makes it a bad year to aerate or overseed your lawn, even if you’re going to do dormant seeding. This is a sure reason to bide your time and overseed at the next opportunity.
You See Frost on Your Grass Each Morning
Every morning when you go out to get the mail, walk the dog, or start your car you may notice that the grass is frosted over. If you see this 2 out of 3 days, on average, it’s too cold to aerate. You could still, however, manage to follow through with dormant overseeding.
How Late Can You Aerate and Seed?
Aeration can be done as long as overnight temperatures are, on average, above freezing. This means that even if your overnight temps are in the 40s, you can still go ahead and aerate. However, if you are using an aerator that creates plugs, you should have a plan in place to break them up before the ground freezes up.
While the best time to aerate and overseed is always late summer or early Spring, it’s better late than never if you have a patchy lawn you need to get ahead of. Always keep your temperatures in mind. This is the best ruler by which to know if it’s too late to aerate and oversees.
For most regions, November would be the cutoff for aeration and overseeding based on historic average temperatures. For a long time that was the rule. But the last few years haven’t always followed these rules. If you have a forecast that predicts 2 weeks of cool-but-not-freezing overnight temperatures and you know you’ve missed the optimal aeration and overseeding window, I would go for it.
While I wouldn’t recommend this for lawns that were being overseeded with just a rake, overseeding a lawn after thorough aeration can improve the odds your seeds will survive. This is especially true with an aerator that reaches deep into the ground and removes cores. These new pores in your lawn are the perfect places for your fresh grass seed to have a better chance to grow in the early stages of winter or to be protected from a cold snap.
Consequences of Aerating and Overseeding Too Late
If you pay attention to the other factors that may affect seed germination, there are few risks to seeding late in the year. However, if things don’t go as planned, there are 3 primary risks or consequences.
Dead Seeds or Sprouts
If you aerate your lawn and then overseed while temperatures are 50F or above for a week and then drop down to solid freezing temperatures for 5 days or more, your seeds will germinate and then the sprouts will die. This is the worst-case scenario of late aeration and overseeding.
Reduced Germination Rate
When seeds are cold for an extended period, they are less likely to germinate and produce plants. If they do produce plants, these plants are likely to have less energy to work with and may even look sickly until they establish a proper source of nutrients. If you seed while the ground is cold and plan on overwintering this seed, the germination rate should only decrease about 5 to 10%. Given that grass seed is typically spread in a thick layer, this will be a hard decrease to notice without looking for it.
Uneven Spread
This is what happens when you aerate, wait to overseed, and then it snows. Not wanting to “waste” the seeds or maybe thinking they won’t last through the winter anyway, they get broadcast on top of the snow. There are two problems with this. The first is birds. Birds will eat grass seed on top of the snow. If any seeds survive the birds and last all winter until the snow melts, the seeds will be washed around in the snowmelt and will likely settle nowhere near where you wanted them to.
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