How tall is the existing grass now? You can let it get to at least 6 inches tall if you can set your mower to a 4 inch cutting height for its first mow.

I'm not sure whether mowing now will do anything to the seeds or not. If you bag your clippings, you might lose seed because it could get sucked up with the grass, but I'm not sure whether mulch mowing is completely safe, either.

I would have thought it's too late to seed in MN already. Where in MN are you? When is your average first frost? For KBG, you should be seeding 6 weeks before average first frost. I did some quick searches and didn't find too many cities in MN with average first frost dates in October. KBG can take 3 weeks to germinate, and that may be longer if the soil has already started to cool off.

Unless you have a warmer fall, you may not have a lot of the new KBG make it through the winter.

For future reference, you should probably overseed in August, preferably by mid August.

I also wouldn't put fertilizer down at the same time as the seed. Grass can use fertilizer at any time it's growing. So when you put it down when you overseed, you give a boost to the existing grass (which you really would prefer to grow slowly) and do nothing for the new grass.

One thing you could do is wait until just before you're supposed to get your first snow and spread some seed then. The freeze/thaw cycles will create cracks in the soil and the snow melting will draw the seed into contact with the soil. It will stay there ungerminated until it warms up in the spring, at which point it will germinate as soon as conditions are right. This gives it a jump start on traditional spring seeding, but it does mean that you can't use a pre emergent in the spring (except for Siduron or Tupersan--one is the brand name and one the chemical name).

bpgreen, very good point about the fertilizer, I'll remember that next time...I'm also going to try spreading seed just before snowfall, good suggestion, i'm curious how that will turn out. I'm in mpls, the first frost usually comes in early october, so I have roughly 4 weeks to get those little guys going. like you said, it probably would've been better to start sooner except for the fact that it was around 90 degrees for much of late august..now the weather is perfect though, 70 degrees and much of the same for the 10 day forecast...if we do have an early frost, i wonder if my existing grass(which is now 2", but will probably be 5" by the end of sept) could actually help protect some of the seedlings from an early frost?..what percentage of seed would I lose to an early frost ..more than 50%? I hadn't thought much about this frost issue, would a light frost do much damage? maybe when I finally do mow I should mulch(rather than bag) that longer grass to help cover and protect the young KBG's...i'm just thinking out loud now...anybody have thoughts on this?

The new grass should be okay if you get a light frost soon. Just remember not to walk on it until it thaws out...or that or any grass will be toast come spring.

I feel your pain on going from summer to freezing with nothing in between. I seeded a week and a half ago on a day that was in the mid 90s. It rained for the next two days and highs have been mostly in the 60s and 70s since. Our average first frost is supposed to be about Oct 10. To speed the germination, I presoaked the seeds which seemed to help. I did that with wheatgrass seeds. Since KBG seeds are so small, it might be harder to do with those.

It's hard to say how much you could lose. KBG can be slow to germinate, but if conditions are right, it can sprout in a week or so. If frost is predicted, you might want to water the lawn that evening. Water takes longer to cool down so it can slow the freezing.

I don't think the existing grass will help protect from freezing, at least not much, but if it will only be 5 inches tall by the time the new grass is growing, I'd just wait as long as possible before mowing.

Say bpgreen - when you soak those seeds, how do you spread them afterward? Seems like that would be a hassle since I;m sure you wouldnl't want to let them dry out after that.

I seeded a couple of native grasses (western wheatgrass and streambank wheatgrass). They're much larger than KBG seeds--about 115,000-150,000 seeds per lb vs more than a million in a lb of KBG seeds. So I soaked them for a day, then carried the bucket with seeds and water around, pulling handfuls of seeds out and spreading them by hand. They're so big, hand spreading works better than trying to use a broadcast spreader anyway.

I think with something like KBG seeds, you soak them for a day, then spread them to dry for an hour or so. You don't want them to get completely dry, just dry enough so they don't stick together and so they'll go through the spreader.

Okay, thanks. Was curious about that since I've heard it mentioned before.

I read something about it that said that it might be more trouble than it's worth with the need to dry before spreading. I decided to go for it because I would be spreading by hand anyway. Even spreading by hand, I found that it worked better if I would pour off the water so the seeds weren't soaking wet, just damp.

Frost won't hurt the grass. I seeded in late October last year and had good germination (I checked the soil temp before seeding), and the grass survived the winter just fine. It did get consistently cold later than normal last year though.

Grass seed germination isn't dependent upon your first date of frost - it depends on soil temps. If the soil is at least 60 degrees, the seed will germinate. The soil temp, not the air temp. Soil cools at a slower rate than air does. You can get a soil temp thermometer from a garden center.

Deanna

Thanks gardenfanatic...yes, you're right. I asked my my golf course super and he agreed that frost won't kill seeds....though he said it's not ideal for germination.