If you’re wondering what the best temperature to grow grass seed is, you’re in the right place. Here at Jonathan Green, we have helped people sow and cultivate lush green lawns for over six generations. Read our quick guide to ideal grass seed germination temperatures below to avoid common mistakes.
When is it too hot or too cold to plant grass seed?
Grass seeds like warmth to germinate. Both hot and cold weather can stunt growth, so it’s good to think about soil temperature and 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 on standby until Fall.
Cool Season Grass Germination Temperature
Cool season grass seed gives you a year-round vibrant green lawn, so it pays to get it right first time. These seeds need a soil temperature of 50°F to 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 cool season grass seed is planted in Spring, it’s highly unlikely you’ll have the right soil temperature, causing it to germinate way too slowly. When there is a lot of rain, it will get waterlogged and rot. If the weather gets too hot too quickly, the heat could prevent germination.
When the daytime temperature is below 60°F, then soil temperature will be below the minimum 50°F, making it too cold to grow. While frost doesn’t kill grass seed, the temperature in which it occurs will prevent any seedlings from lasting.
Your germination window closes at 50°F
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, so they go dormant. This is the perfect window where your grass seed has just enough warmth and plenty of water to germinate, as well as 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.
Summary
While the best soil temperature is 50 to 65 degrees, we understand that some folks need a different planting window. Drop us a line before you prep your soil, and we’ll help you get it rooted right first time!