If you want to plant new grass on your property, you might wonder whether the weather is quite right for the job. Is it too cold outside? You don’t want to go to all the trouble of planting grass seed just to have no chance for success because of the temperature outdoors. So, how cold is too cold to plant grass seed?
The Short Answer
Generally speaking, if the daytime temperature is cooler than 60°F, that means that your soil temperature will be lower than 50°F. In this case, it’s probably too cold for you to plant grass seed. If there is still the possibility of frost outside, then it’s definitely too cold to plant grass seed.
Why You Shouldn’t Plant Grass Seed When it’s Too Cold
The problem with planting grass seed in inhospitably cold soil is that it’s likely to end up rotting or washing away in the heavy spring rains.
And if it does germinate and then gets hit with frost, say goodbye to the money you spent on seed.
In either case, that’s certainly not what you want to happen to your seed investment.
Grass seed is expensive and planting takes time. It’s better to plan in advance and make sure you are doing things at the right time of year.
My advice (if you’re planting in spring) is to wait until you hit the temperature benchmarks I lay out in this article, and then wait a week.
This makes your 10-day forecast effectively a 17-day forecast and ensures you’re in the clear. That week’s delay won’t make a difference by the time summer rolls around – your lawn will still look great.
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It’s All About Germination
Grass seed cannot flourish in cold soil because it requires warmth to germinate.
But you should be aware that it’s not only cold weather that can interfere with growth. Extremely hot weather can also cause problems.
Make sure you check the weather forecasts and keep soil temperature in mind before planting grass seed. This is important whether you’re starting over and planting a full lawn or just dealing with bare patches in your grass.
Best Temperature for Planting Grass Seed in the South
If you’re in southern and southwestern areas of the United States and you have a warm-season grass, then you should sow your seeds when the air temperatures at night are only a little above 65° in the springtime.
This will set you up to start getting the results you desire when the warmer weather arrives.
Best Temperature for Planting Grass Seed in the North
If you have a cool-season grass, however, it’s generally best to plant in the autumn, though you can have success in the spring if you use the right product to combat annual weed pressure on your new grass (I use and recommend this starter fertilizer + weed preventer from Scotts).
With cool-season grasses, you need to have a soil temperature of about 50°. It shouldn’t be any higher than 65°.
September is often a good month to plant cool-season grasses. One reason why it’s often wise to avoid spring is that if you end up having a huge amount of rain, the seed could become waterlogged or wash away.
Combine that with the pressure from aggressive annual weeds like crabgrass, and the brutal heat of summer (tough, even on established cool-season grass lawns), and your new lawn has a steep hill to climb.
When you plant your cool-season grass in September, you will give the seeds the time they require to germinate in the warm soil. This is very important.
Also, the air temperature will be dropping a bit when the grass starts to sprout. Other kinds of plants (such as weeds) will go dormant at this time, giving your grass even more room to flourish.
It’s important that your grass be properly established by the time the winter arrives, which is why I usually recommend September.
When it’s Too Cold to Plant Grass Frost Can Kill
While it’s certainly true that frost can kill grass seedlings, if you’re smart and follow my guidelines on when to plant, your grass should be fine.
This is because if you plant your cool-season grass at the beginning of autumn, it will have time to get established and should be able to withstand freezing when the colder weather eventually arrives. When the winter does get into full swing, the grass will go dormant. It will then re-sprout when spring rolls around.
Choose the right kind of grass seed for your climate and follow the guidelines on when it should be planted.
If you live in southern areas of the United States, you will probably choose a warm-weather variety of grass seed.
If you live further up north, you will want a cool-season species.
And I usually recommend a blend of different grasses that thrive in your region. This ensures good coverage in sun, shade, and different areas of your lawn.
Where one grass type struggles, another will thrive.
How to Test Soil Temperature
If you don’t have one already, you will need to invest in a soil thermometer. You should be able to find one of these locally for a very reasonable price, so don’t worry about breaking your budget.
I recommend that you look at the selection of soil thermometers at your local garden center. There are often ones available that cost only a few dollars, but you can get one on Amazon as well if you prefer.
Look for a glass bulb thermometer. Its metal point should be strong so that it will be sturdy enough to push down into the soil.
My Tips for Measuring Your Soil Temperature
- Take soil temperature at the correct depth. Find out the recommended planting depth for your seed (typically, it’s about 1/4″ or so) and then measure soil temperature at that depth.
- Make a pilot hole in the soil using a screwdriver. This will help prevent you from breaking your soil thermometer when you push it into the soil.
- Refer to your thermometer’s directions (all thermometers should come with instructions). If you have a glass bulb thermometer, you will need to ensure that it is securely touching the soil. Poor soil contact makes your effort a waste of time. Give it a few minutes for the temperature to be properly registered.
- Shade the thermometer. If the sun is shining very brightly outside, it might affect the temperature reading. This is why you should give your thermometer a bit of shade while you’re using it. You can just use your hand to shade it. This will help to make sure that the reading you get is an accurate one.
Best of Luck Planting Your Grass Seed
Now you know how cold is too cold to plant your grass seed (anything below 50 degrees Fahrenheit).
And once it’s warm enough to plant, make sure you water your new seed properly, and use the best mulch (I recommend screened compost) to help keep it moist.
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