For homeowners trying to establish a new lawn before Old Man Winter arrives, a common question arises: Will frost kill grass seed?
The good news is frost itself usually won’t kill off your new grass babies. However, consistent freezing temperatures for an extended period can potentially damage tender new seedlings.
In this post, we’ll look at optimal seeding times, how cold is too cold for grass, tips to protect your new lawn into winter, and everything you need to know about frost’s effects on grass seed.
When to Seed a New Lawn Before Winter
Timing is critical if you’re hoping to plant cool season grass varieties like fescue or bluegrass in the fall before winter arrives (Read our tips, How to plant in winter). Here are some guidelines on ideal seeding windows by region:
- Northeast: Seed by late August – early September
- Midwest: Seed by early to mid September
- Northwest: Seed by late September
- Southeast: Seed September – November
Seeding too early can encourage weed growth before the grass fills in.
Seeding too late doesn’t give new grass enough time to establish before harsh winter weather hits.
Aim for seeding about 6-8 weeks before your average first frost date.
This gives enough growing time for new grass plants to develop strong root systems and enter dormancy better prepared for cold temps.
Fall planting also offers key advantages over spring:
- Soil temps are still warm, promoting faster germination
- Less weed pressure compared to spring
- Less water needed due to cooler, wetter fall weather
- Full growing season the following spring
Now let’s look at how cold weather actually impacts newly seeded lawns…
Does Frost Kill Grass Seed?
Before we look at how frost affects newly seeded grass, let’s clarify the difference between a frost and a freeze.
Light frosts occur when temperatures dip below freezing but only for a short period overnight.
This forms frost on surfaces but doesn’t penetrate deep into the ground.
A hard freeze happens when temps remain below freezing for an extended time – usually at least 8 hours overnight – leading to frozen soil.
When it comes to grass seed, light frosts generally won’t kill off new seedlings.
In fact, most cool season grass varieties can tolerate temps as low as 20°F once established. However, hard freezes can damage, but not always kill, tender new grass plants.
Here are some temperature thresholds to be aware of with new fall plantings:
- Light frost (above 27°F) – Generally safe for new seedlings
- Moderate freeze (24°F to 20°F) – Potential damage, but plants recover
- Hard freeze (below 20°F) – Can be fatal for unestablished grass
Younger grass plants are more vulnerable to cold injury, while mature, established lawns can better tolerate freezing temperatures and even light frosts.
So while frost itself doesn’t directly kill grass seed, consistent heavy freezes can potentially be harmful depending on the growth stage. Next let’s look at ideal temperatures for germination.
Optimal Temperatures for Seed Germination
Cool season grass species can germinate in a wide range of soil temperatures, but there are ideal temperature ranges for quick, uniform sprouting:
- Bluegrass: 50°F to 65°F
- Fescue: 60°F to 75°F
- Ryegrass: 45°F to 65°F
The minimum soil temperature for these grass seeds to germinate is around 45°F. Growth slows considerably below 50°F and stops below 40°F.
During cool fall months, you can use a soil thermometer to check that temperatures are still satisfactory for germination and growth. If soil is too cold, germination and establishment will be very slow.
There are a few tricks to help regulate soil warmth if temperatures are borderline:
- Use row cover fabric to trap heat
- Mulch seeded areas with straw to insulate soil
- Water lightly to warm the soil
- Avoid excessive watering that cools soil
Protecting Newly Seeded Grass from Frost
If temperatures start dipping low after you’ve planted new grass seed, there are a few steps you can take to protect the tender new seedlings:
- Cover with frost blankets or fabric row covers overnight to provide a few degrees of protection. Remove during the day.
- Apply a thick layer of straw mulch over seeded areas. The straw acts as an insulator, preventing soil temps from fluctuating too rapidly.
- Avoid heavy watering that can saturate the soil and make it prone to freezing. Light, infrequent watering is best.
- Apply a high potassium fertilizer to encourage root growth before dormancy. Stronger roots withstand cold better.
- Consider installing a cold frame or hoop house style cover if extremely cold temps are expected for long durations.
Also avoid foot traffic or activity on newly seeded areas when frosts are likely, as this can damage young tender grass plants.
Caring for Seeded Lawns Over Winter
Caring for your newly seeded lawn doesn’t stop once cool weather settles in. Here are some tips for looking after fall plantings over the winter:
- Continue watering periodically during dry spells or stretches without rain/snow. Avoid saturated soil that freezes readily.
- Hold off on first mowing until early spring after grass resumes growth. Let new seedlings continue establishing over winter without cutting.
- Fill in thin patches by overseeding before the ground freezes. This gives new seedlings a head start come spring.
- Avoid excessive foot traffic on seeded areas all winter. Walking on frozen new grass can damage shoots and roots.
- Apply a winterizing fertilizer high in potassium in early fall to prep plants for colder temps.
- Check for erosion issues and re-seed washed out areas. Use erosion control blankets if needed.
With proper ongoing care, your new grass plantings should come out of dormancy thick and lush in spring!
FAQ
Let’s review some frequently asked questions about frost and grass seed:
- Can frost kill grass seed that hasn’t sprouted yet?
No, frost only damages visible grass leaves and crowns. Dormant grass seed can withstand very cold temperatures when planted in the soil.
- How low can temperatures go before damaging new seedlings?
Most cool season grasses tolerate light frosts down to 25°F. Prolonged hard freezes below 20°F are most likely to injure new growth.
- When is it too late to plant grass seed before winter?
Ideally seed at least 6-8 weeks before your first average fall frost to allow for germination and establishment before winter dormancy.
- Will frost undo all my seeding work?
Not necessarily! Frost can set back new growth but doesn’t kill the grass outright. With proper care, new seedlings will bounce back in spring.
- Should I overseed in fall or wait until spring?
Fall overseeding allows new grass to get a head start before the main spring growing season. Just get seed down at least 6 weeks before heavy frosts start.
Recap
To quickly recap what we’ve covered about frost and grass seed:
- Light frosts generally won’t kill new grass seedlings
- Consistent heavy freezes below 20°F can potentially damage tender new growth
- Ideal soil temperature range for cool season grass seed germination is 50°F to 65°F
- Use row covers, straw mulch, and cold frames to protect fall plantings from frigid temps
- Continue irrigating and overseeding into early winter to boost spring growth
- Well-established lawns can better tolerate cold winters than newly seeded ones
While frost itself rarely wipes out grass seed, subfreezing temperatures over extended periods can injure young tender plants. Follow the tips above to give your new fall lawn the best shot at thriving through winter.
Final
Establishing a new lawn in fall before winter arrives requires careful timing and some frost protection measures. But the benefits of fall seeding make it an ideal time to start a lawn from scratch.
By understanding how cold affects grass seed and seedlings, using frost covers, monitoring soil temperatures, and continuing care into winter, you can set your new grass up for success.
While frost may temporarily setback new growth, it rarely kills off properly-cared-for seedlings outright. Your new lawn will burst forth healthy and thick after emerging from winter dormancy.
With the right preparations, there’s no need to fear Old Man Winter ruining your fall lawn projects. Just be strategic in planting timing, choose cold hardy grass varieties suited for your zone, and provide a little TLC through the cooler months.
References
[1] https://mybackyardlife.com/will-frost-kill-grass-seed/
[2] https://www.jonathangreen.com/resources/does-frost-kill-grass-seed.html
[3] https://peppershomeandgarden.com/does-frost-kill-grass-seed/
[4] https://extension.umn.edu/lawncare/fall-lawn-renovation
[5] https://www.familyhandyman.com/list/what-is-the-best-time-to-plant-grass-seed/
[6] https://www.gardeningknowhow.com/lawn-care/seeds/germination-temperature-for-grass.htm
[7] https://www.turfcaresupply.com/blogs/news/what-temperature-does-grass-seed-germinate
[8] https://www.lawndork.com/lawn-basics/frost-seeding
[9] https://extension.umn.edu/lawncare/caring-your-lawn-winter