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I know (now) that the best time to overseed a lawn is in the Fall. I obviously missed that window so I have to make do. I've read that the 2nd best time to overseed is early Spring. But how early is too early? I live in the middle of Pennsylvania and temps are currently running about 30-50& deg;F.

What temperatures should I be looking for to overseed? Will a heavy frost damage new grass seedlings? I'm anxious to get going (it will be 60 °F on Saturday) but I don't want to rush it if I'm going to do more harm than good.

  • I always reseed in the spring, because there is always winter damage. Temperature is not important because the seeds will eventually sprout; as long as they don;t get eaten first. I always put down a mixture of seed, starter, top soil, and peat moss; I never just throw seed around. Since i have been using that technique I have had "perfect" results. – sborsher Mar 23 '15 at 18:56
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Dormant Overseeding! Read about it. Do it. I live in Ohio and the freeze thaw cycle that heaves the ground up and down pulls the seed down into it for great soil contact. Followed by wet springs... bingo. I overseed just before Christmas every year and my suburban lawn is the envy of the neighborhood.

I don't think the seed will germinate until nighttime temperatures reach around 50.

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    Also Known As Frost seeding (in the agriculture community more than the lawn community.) – Ecnerwal Mar 19 '15 at 14:29
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    Thanks for the tip. Sometimes the hardest part is knowing what phrase to Google. My takeaway is that it is never too cold to overseed. The grass may not germinate until it gets warmer but that is OK by me. – bMcNees Mar 19 '15 at 14:44
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If you're seeding in the spring you need to wait until soil temperature is at least 50-65 degrees before most grasses will germinate effectively. Even though daytime temperatures may be in the correct range the soil will take time to warm up.

Edit to answer comment and updated temperature:

At this point in the season you've missed the opportunity to reap the benefits of winter sowing. It's the freeze/thaw cycles that give the benefit. As the soil freezes it opens up pores which then close as the soil thaws.

If you put down seed now, before ideal conditions for germination it's going to just sit there. You'll lose some to birds, squirrels and possibly some to frost if you get a warm spell that begins the germination process followed by a very cold day.

You also won't know when the seed starts to germinate which can cause issues with providing proper irrigation.

I think you'll have more success at this point waiting until soil reaches at least 60 degF and is rising with no signs of frost or sub freezing temperatures in the long range weather forecast.

  • If I seeded the lawn now will it kill the seed? Or will the seed lay dormant until it warms up? – bMcNees Mar 21 '15 at 12:07
  • @bMcNees I updated my answer to address your comments. – OrganicLawnDIY Mar 21 '15 at 16:07

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