Will Frost Kill Grass Seed And How To Help New Turf Survive

Blades of grass covered in frost
(Image credit: ligora)

If fall is near yet you never got around to seeding the lawn, and you might be wondering about seeding now. The big question is does frost kill grass seed. In other words can grass seed survive the upcoming frost? The answer to this question will determine whether you wait until the spring to sow or if you should risk potential grass seed freezing. Keep reading to learn about fall grass seeding and how to protect new grass from frost.

Can you Sow Grass Seed in the Fall?

The short answer to sowing grass seed in the fall is yes, but it gets a bit more complicated. First it depends on what type of grass seed you are sowing. The types of grass you sow will either be of the cool season or warm season variety. Warm season grasses such as Kentucky bluegrass or Rough bluegrass are slower to germinate and establish enough to endure frost while cool season grasses like Ryegrasses do so more rapidly allowing them to establish maturity quickly enough to withstand winter weather.

The general rule of thumb is to avoid seeding after the end of September. However in the case of new construction, it is better to attempt to get some germination than none at all to slow erosion.

In the case of over seeding into existing turf, there is more leeway. If temperatures are still mild in October for instance you may still have enough time for seed to establish before winter. Maybe.

The other option is called dormant seeding.

What is Dormant Seeding?

Dormant seeding can occur with any type of turf grass. Basically you sow when temperatures are too low for the seed to germinate before the onset of winter. This can be a bit tricky. If seeds germinate prior to winter they will likely die as they haven’t matured yet.

Watch the weather forecast and find a time when the soil is malleable enough that seed can be worked in and yet the air temp is cold enough the seeds won’t germinate. Daytime temperatures should be consistently below 50 F. (below 10 C.) with soil temperatures in the low 40’s (below 7 C.) or below. The goal is that the seed will lie dormant during the winter months and then germinate as soon as conditions warm in the spring.

Dormant Seeding Tips

To ensure the success of dormant seeding, beyond watching the temperature, broadcast seed on a prepared bed at a higher rate than normal. If an available option, use a slice seeder which will create furrows in the soil giving direct seed to soil contact.

If using mulch, avoid dark colors that warm and encourage early germination. Instead use loose straw or straw netting which will help to hold the soil together.

New Grass Freeze Warning

Your newly sown grass seed won’t freeze, the danger is if it germinates too quickly before winter weather. The young tender shoots won’t have established enough to survive the harsh conditions.

If you already have a young lawn growing and winter weather is approaching you may wonder how to protect it.

Seeing the grass brown in the winter may worry some homeowners but grass never really stops growing, not even during the winter. It just grows at a much slower rate or dormancy. If however temperatures drop below 20 F. (-7 C.), the turf may become permanently damaged.

Nonetheless you can take some steps to prevent any winter injury. Frozen grass blades contain ice crystals between the cells which help to protect them from injury. If you tromp on them, drive on them or let the dog and kids run amok, you are risking damaging the lawn. If this happens the cells are pierced by the frozen ice crystals resulting in a brown and unsightly lawn come spring

Never fertilize in the winter -- only in spring and fall.

In the spring, give the grass some time. Brown grass does not necessarily mean dead grass. Also wait to mow until the grass is at least 2 inches (5 cm.) in length. Even then be sure not to mow the grass back by more than 1/3rd to allow it to continue to photosynthesize and grow.

Amy Grant

Amy Grant has been gardening for 30 years and writing for 15. A professional chef and caterer, Amy's area of expertise is culinary gardening.