Dormant seeding: sowing grass seed in winter

What dormant seeding is and the soil temperature rule

Dormant seeding means putting grass seed down when the ground is too cold for it to sprout. The University of Minnesota Extension says it can be done any time soil temperatures are below 40°F, which in most of Minnesota runs from early November to the middle of March. Soil temperature is the rule, not the calendar date, so the Minnesota dates will not fit every state.

The seed then rides out winter and uses the natural freeze and thaw cycle to work into contact with the soil. Minnesota says early winter gives more chances for seed to reach the soil, and late winter can work too. When soil and air rise above 40°F in spring, the seed may begin to germinate and emerge.

Where it works

Minnesota says dormant seeding works with all the cool-season lawn species grown there: Kentucky bluegrass, fine fescues and tall fescue. It fits best where winter keeps the soil cold. Our reading of the 40°F rule is that a region where soil rarely stays that cold has no real dormant window, so ask your county extension office before trying it.

It suits thin turf and bare patches. For a lawn that only needs more density, Minnesota says no site preparation is needed. Warm-season grasses such as buffalograss can also be dormant-seeded, but they germinate at warmer soil temperatures, and Minnesota warns that summer annual grassy weeds like crabgrass will likely compete harder against them.

How to do it

Buy a mix of species suited to your site, and buy 10 to 20% more seed than you need so you can overseed any area that fails in late spring. Bag heavy tree leaf litter first, because leaves can keep seed off the soil. Spread the seed on dry ground. A drop spreader is best for larger areas, and Minnesota suggests sowing half the rate in each of two opposite directions for even coverage. Raking is not needed.

On bare soil, especially a slope, use a germination or erosion control blanket to hold the seed. If you are replacing a whole lawn, Minnesota describes spraying glyphosate in late October and leaving the dead residue in place to hold the seed over winter. Read and follow the product label for any herbicide.

For how this compares with a normal overseeding, see our guide to when to overseed a lawn.

Risks, including a warm thaw

Minnesota lists two drawbacks. Most crabgrass preemergent herbicides cannot be used, because they will affect the grass seed. And if the seed germinates and the spring turns warm and dry, the seedlings can dry out if nobody waters them.

The Extension sources we read do not agree on whether homeowners should try it. Illinois Extension calls winter dormant seeding difficult, occasionally done by professional groundskeepers and not suggested for homeowners, and names late summer to early fall as the better window, with April second. Penn State Extension also names late summer the optimum time in most of Pennsylvania, because warm soil germinates seed faster and the seedlings get two cool growing seasons to establish. If you can seed in late summer, that is the safer choice by these sources' reasoning. Dormant seeding is the option for a lawn you could not seed then.

Minnesota has not observed birds or other animals eating dormant-sown seed. If that worries you on thin turf or bare soil without a blanket, it suggests sowing in late winter or early spring instead. For open or exposed areas over a quarter acre, it says hydromulching can be a cheaper way to establish grass, though freezing air temperatures can limit the equipment.

The spring check

Watch for emergence once soil and air pass 40°F. Keep the seedlings from drying out; irrigation systems may still be off in early spring, so Minnesota says the site may need manual watering with hoses.

Mow once most seedlings are above your normal mowing height. Minnesota says at least 3 inches is best; our guide to mowing new grass has more. A starter fertilizer with nitrogen and phosphate is generally recommended around the first mowing, especially if soil is low in phosphorus. If summer annual grassy weeds like crabgrass show up, Minnesota says they can be treated with a post-emergent product in early summer, after the second or third mowing. Reseed any bare areas in late spring with the extra seed you bought.