I over-seeded and applied starter fertilizer today, but I neglected to cut the lawn short first. Will it be OK to mow in the next couple of days before the tall fescue blend germinates?
If all you did was through some seed out then you weren't going to get much germination to begin with so go ahead and mow. Mulching with a sharp blade would be best.
If you rolled after you set out the seeds then probably not a problem. If not, mowing would simply suck up all the seed you just put out. I spose if you are not bagging, it wouldnt do much harm to the seeds (they probably have not started to germinate yet...) They'd just get a wild ride as the blades sucked them up and spit them out the chute....
If it were me, i'd leave it alone and not mow for a few weeks at least.
With all the rain I've had, I have to mow, regardless. But I mulch mow anyway, so if the seed is not stuck to the soil, already germinating or growing, it's only gonna whirl around the mower deck and not going far, and with another rain it's right back in soil contact again. If there is any seed loss, it's okay with me as long as I can keep the bulk of the seed in good contact to grow.
I neglected to say that I core arreated before I sowed. Thanks for sharing your experiences.
It's a tough call but mow when you absolutely have to. Luckily you core aerated so seeds there should be well protected. I would not mow too close out of concern for the seeds/seedlings. I have mowed at 3 1/2 inches a couple of weeks after overseeding and the hair-like seedlings did fine with the turbulence of cutting and running over them with the riding mower. Too young though and you could have problems.
There is another aspect that should be considered, and the only reason I mention it is because it caused me a lot of grief. No matter how much germination is still to be done, if you are expecting heavy rain and have areas that the rain will run over, don't let your grass get over 3.5-4" tall...and that might be too tall if it's a good tropical type storm.
What happened to me was I waited too long to mow because I was trying not to mess with the new seedlings, the grass grew to around 4-5" tall and we got a cow-on-a-flat-roof type rain which quickly matted down the seedlings. When that happens those seedlings were too young to raise back up (even with light raking), and that area has to be re-seeded again...or mine did. Thought I'd pass that on if it hasn't happened to you yet.
Cow-on-a-flat-rooftop- type rain. Now that is a visual (and an audible.) I keep seeing those poor cows on the porches after Eric in Texas. Interesting experience you had with your grass. Who would have thought the tall grass would mat and smash the seedlings? We are in the midst of a three year drought so we are due a flood. Thank you to everyone for sharing your experiences.