Overseeding: Do it Now in the North
With Columbus Day here, folks in the most northern states in the U.S. and much of Canada are running out of time for overseeding the lawn. Late summer and fall is the best time for this activity in general, but the clock long ago started ticking on the ideal window.
The issue is that the young grass plants need time to establish themselves before it gets bitterly cold. Any seed mix you put down now should probably have Kentucky bluegrass and perennial ryegrass in a high percentage; the ryegrass because it germinates quickly and the bluegrass because it tolerates cold so well. Fescues are the best grasses overall for the North, but they do take a long time to germinate (14-21 days) and they are the most susceptible to cold damage of not fully established.
OTHER TIPS ABOUT SEEDING NOW:
1) If you do seed, be sure to rake away any excess thatch layer or dead grass first to create good seed to soil contact.
2) If you feel your soil is compacted, aerating prior to overseeding is a good idea;
3) Cover the newly seeded area with a thin layer of compost rather than straw; it will be cheaper and better for the lawn; it also looks better.
4) Water the newly seeded areas daily until they fully germinate, unless of course we get rain naturally.
5) Some people advocate dormant winter seeding, that is putting the seed down after the ground freezes and then letting nature take its course. The idea is that the grass will germinate on its own by spring without the necessity of daily watering. I’m not a fan of this, however, because so many things can go wrong (birds eating it, freezing and thawing, erosion etc.) between now and then.
6) Applying an organic fertilizer rich in potassium this fall will help the lawn through winter.
7) Don’t mow the lawn for the first time until the young grass seedlings are four inches tall.
8) Don’t allow the leaves to remain on the lawn, especially in the newly seeded areas; the leaves will mat down the grass. You may find you have to rake lightly, or use a blower, to remove heavy layers of leaves.