If your lawn is a cool-season grass type (tall fescue, usually), it should be overseeded in early autumn, not spring. (Warm-season turf like zoysia is not overseeded.) If you have to repair specific areas of the lawn, you can sow seed soon (April is generally a decent time so the soil has warmed) as needed to discourage erosion or weeds from causing problems, or patch bare areas with sod (easier than seed). There are a number of reasons sowing fescue seed in spring is discouraged, but if you can't wait until September or so (the ideal seeding timeframe), then you can put down seed in a couple weeks. Spring-sown seedlings will face potential problems from weed competition (and few herbicides can be used in conjunction with seeding, especially given Montgomery County lawn pesticide restrictions), late frosts, and heavy rainstorms that could erode or dislodge seedlings. In early autumn, warmer soil temperatures can help roots establish faster, and while winter annual weeds may be germinating, they usually don't need to be treated as they'll merely die out on their own by late spring.

We recently overhauled all of our lawn care web content. You can find connections to all of the new pages on our Lawns for the Maryland Home Landscape page. The Maintaining an Established Lawn page includes recommendations and procedures for overseeding.

Any time you sow grass seed, it needs careful attention to watering, both to initiate germination and to avoid killing the seedlings if they dry out while growing roots. (They are not very tolerant of getting too dry during this critical stage.) We would not suggest overseeding during any period of time that you can't monitor the lawn for watering needs, since seed/seedlings may need a light watering several times per day depending on soil moisture-holding capacity and the weather.

Miri

This is wonderful information, thank you! I have been researching on the Extension website for some time, but didn't know the lawn care pages had been updated. I will check those out.

I don't know what grass I have now, but the patching I've been doing (and what I intended to overseed with) is the Jonathon Green Delmarva blend, which looks to be tall fescue like you mentioned. That being the case I'll wait until fall to overseed, but I'll patch the bare spots when I get back (which I believe was mostly some kind of crabgrass? Something that spread quickly but died out over winter, and seemed to all be connected--it gets uprooted easily in big chunks with a dethatching rake). That will also give me more time to get soil test results back.

I'm also looking into leveling my lawn, as there are a lot of ruts and divots, etc. Is there a better or worse time of year to do that? Also, do you have a recommendation for straw or peat moss to cover new grass seed to keep the birds off?

Thank you so much,

David 

Follow up question:

You said better to use sod for bare patches than seeding. I have several areas of lawn that I'm going to convert to beds. Would it be better to transplant sections of the existing lawn to the bare patches rather than seed them?

Thank you again.

Crabgrass does die completely over the winter (only seeds that sprout in spring create a new generation), but it stays more clumped and doesn't "run" with long stems that root as they spread to the extent that other grassy weeds can. (It does root more as it grows wider, but the plants still generally remain discrete tufts.) In comparison, there are several warm-season perennial weedy grasses that superficially make look similar this time of year, since they would not have broken dormancy to regrow yet this early, and their foliage is still brown and dead. They do spread more aggressively and are harder to pull up in one piece. Common culprits are Nimblewill (a native species) and Bermudagrass (non-native and very hard to eradicate). These two species have to be dug out or spot-treated (once they are actively growing again) with systemic herbicide in order to eradicate them before you can patch areas affected by their takeover.

As for leveling-out ruts or other uneven areas of the lawn, the best time to do it may depend on the urgency. If it's causing erosion problems, a trip hazard, etc., then address it as soon as you need to and patch the lawn accordingly (seed or sod). If it can wait, level that area just before seeding or sodding this coming autumn, since that's the best time of year to plant fescue and other cool-season turfgrasses. Tips for leveling uneven areas can be found in the new lawn care pages, but it's essentially the same (on a smaller scale) as one would do for renovating an entire lawn.

It probably doesn't matter too much what to cover newly-sown grass seed with, and we do mention using straw in those new pages. Seed should not be covered too fully so you don't smother it and prevent germination; just enough to help hold humidity around seeds or slow the drying (a bit like mulch) of the soil surface, discourage erosion, and to a lesser degree, discourage seed consumption by birds or rodents. Peat moss would not be a very useful top-dressing in lieu of straw, as it's naturally hydrophobic (water-repelling) when it gets very dry, and it might be fairly acidic (unless treated by the manufacturer with limestone to balance pH). If you cover the seeds with any soil-like material, compost or good-quality topsoil would be better (though straw by itself can also work).

Miri