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How cold is too cold for grass seed?

Seeding Spring Fall Winter
4 min read

If you’re wondering how cold is too cold for grass seed germination use our rule of thumb and check the weather reports. If the daytime temperature is below 60°F then soil temperature is below 50°F, making it too cold; if there is frost or still a danger of frost, then it’s too cold.  If it’s too cold, the grass seeds will likely rot.

Here at Jonathan Green we have helped people sow and cultivate lush green lawns for over six generations. So, we know when customers call to ask if it’s too cold for planting grass seed – that thus far, nobody gave them the correct information on their planting window. Or, they have already planted out of season and need our help urgently! For tailored advice, call or visit us for a fast and friendly fix for your lawn queries.

When it’s too hot or too cold for grass seed

Grass seeds like warmth to germinate and because both hot and cold weather stunts growth it’s good to think about soil temperature as well as air temperature plus the upcoming weather when you’re about to reseed, fix bare patches or start a lawn from scratch.

Warm-season grass growers of the South and Southwest sow when nighttime air temperatures are just above 65°F in Spring and get great results as things start getting hotter. However, smart cool-season grass growers with the best lawns keep their seed by until Fall.

Cool season grass seed gives you a year-round vibrant green lawn so it pays to get it right first time, at reseeding time and when there are bare or problem patches. These seeds need a soil temperature of 50 and no more than 65°F, but take care; we put down this grass seed in Fall (specifically we plant in September, or with care, October) instead of Spring with good reason. When it’s put down in spring, it’s highly unlikely you’ll have the right soil temperature causing the seed to germinate way too slowly.  If you get a lot of rain, it will get waterlogged and rot, if the weather gets too hot too quickly the heat could prevent germination.

Not to mention, you should not treat your lawn for weeds until you have mowed the new grass four times. A springtime seeding can be done, but it needs careful planning, and could cause a little more heartache than any lawn should.

Your planting window closes at 50°

Around September though, grass seed has plenty of time to germinate in warm soil, which is key for cool-season grasses. Whenever it does start to sprout the air temperature is dropping. As this happens it gets too cold for other seeds, plants and weeds, which go dormant, allowing your grass seed just enough warmth and plenty water to germinate, and the space to grow fast.

Fast growth before it gets too cold for the grass seed is what you need. That way you have young tender grass that is well established and ready for winter. Once the grass is up and can be cut to the usual 2 or 3 inches then it is ready to be mowed. This gives the grass a strong crown, and a good indication that your lawn will flourish in the summer.

So, when working with cool-season grass, planting in a soil temperature of below 50°F is too cold for grass seed. Like we said before, some folks need a different planting window so drop us a line before you prep your soil and we’ll help you get it rooted right first time.

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