The best temperature to plant grass seed depends on the type of grass you’re planting. Cool-season grass seed sprouts best in fall, while warm-season grasses are best seeded in spring.
- Seed cool-season grasses in fall, when soil temperatures are 50–65℉ (10–18℃).
- Cool-season grasses include bluegrass, rye, and fescue.
- Seed warm-season grasses in spring, when soil temperatures are 65–70℉ (18–21℃).
- Warm-season grasses include Zoysia, Bermuda, and centipede grass.
Table of Contents
Best Temperature to Grow Grass: Warm-Season and Cool-Season Grasses
Grass seed is triggered to germinate or remain dormant based on the temperature of the soil it has been cast upon. For this reason, a soil temperature map is the most accurate tool to determine whether or not it’s time to seed your lawn. However, you can make a good judgment of soil temperatures based on daytime air temperatures. Here’s how.
Cool-Season Grass Seed
- Grows best with soil temperatures 50–65℉ (10–18℃).
- Soil typically reaches optimal temperature when air temperatures are 60–75℉ (15–24℃).
Warm-Season Grass Seed
- Grows best with soil temperatures 65–70℉ (18–21℃).
- Soil typically reaches optimal temperature when air temperatures are 70–90℉ (21–32℃).
Fall vs. Spring: Grass Seeding for Best Results
Cool-season grass seeds grow best in fall, experiencing strong germination and great growth before winter, then a second strong growth period in spring. Warm-season grass seeds benefit from being seeded in spring, where they will sprout and grow vigorously through summer.
Because cool-season grasses begin to slow in growth or resist germination due to high heat, it is not optimal to seed cool-season grass in spring. Similarly, growth and germination of warm-season grasses slows or stops as temperatures cool, so seeding warm-season grasses in fall may result in weak grass seedlings that cannot survive the winter.
Cool-Season Grasses
- Should be seeded in the fall.
- Seed at least 6 weeks before the first frost.
- Enter dormancy when soil temperatures go below 40℉ (4℃).
- Enter dormancy when soil temperatures rise above 90℉ (32℃).
- In regions where warm-season grasses go dormant in winter months, overseed with cool-season grass in fall to promote a green lawn year-round.
Warm-Season Grasses
- Should be seeded in spring.
- Seed at least 2 weeks after the last spring frost.
- Enter dormancy when soil temperatures go below 55℉ (12℃).
- Do not enter dormancy due to heat.
Identifying Cool-Season and Warm-Season Grasses
When you are planning to seed your lawn, it’s important to know whether you’re seeding with cool or warm season grass seed. Many commercial grass seeds contain a blend of seed types with different germination and growth rates. Scan the list of grasses included to determine whether the blend contains cool or warm season grass seeds.
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Bermuda Grass
Bermuda is a warm-season grass common across much of the American south, southwest, and transitional zones. When considering seeding with Bermuda, keep these traits in mind:
- Should be seeded in spring.
- Seed when soil temperatures are 65–70℉ (18–21℃).
- Drought-tolerant. Grows well in arid or semi-arid climates.
- Not shade-tolerant. Avoid seeding Bermuda in shady lawns with areas that don’t receive direct sunlight.
- Goes dormant when soil temperatures reach 55℉ (12℃).
St. Augustine Grass
St. Augustine is a warm-season grass adapted to hot, humid climates. It spreads mostly via aboveground stolons or “runners.”
- Grows poorly from seed. Seed St. Augustine only to thicken existing St. Augustine lawns.
- When establishing new St. Augustine, use sod.
- Treat sod like seed. Lay new St. Augustine sod in spring when soil temperatures are 65–70℉ (18–21℃)
- Not drought tolerant and does not tolerate arid or semi-arid climates.
- Shade tolerant and can grow well even without large quantities of direct sunlight.
- Enters dormancy when soil temperatures reach 55℉ (12℃).
Zoysia Grass
Zoysia grass is a warm-season grass that combines some of the benefits of both St. Augustine and Bermuda grass.
- Should be seeded in spring.
- Seed when soil temperatures are 65–70℉ (18–21℃).
- Drought-tolerant. Grows well in arid or semi-arid climates.
- Tolerates light shade. Can grow well in somewhat shady areas where Bermuda grass struggles.
Kentucky Bluegrass
Kentucky bluegrass is a hardy cool-season grass popular from transitional zones to northern areas of the United States.
- Should be seeded in the fall.
- Seed when soil temperatures are 50–65℉ (10–18℃).
- Allow ample time for germination. Kentucky bluegrass can require up to 21 days before it sprouts.
Perennial Ryegrass
Ryegrass is a cool-season grass found across the northeast and the midwestern United States.
- Should be seeded in the fall.
- Seed when soil temperatures are 50–65℉ (10–18℃).
- Sprouts in as little as 7 days, making it a great addition to Bluegrass blends.
Tall Fescue
Fescue is cool season grass suitable for lawns in the cold, northern regions of the US, or as an overseeded seasonal grass in warmer regions.
- Should be seeded in the fall.
- Seed when soil temperatures are 50–65℉ (10–18℃).
- Can be overseeded on Bermuda, St. Augustine, and Zoysia lawns in fall. Fescue will remain green throughout the winter in southern regions, resulting in a green lawn while warm-season grasses are dormant.
What Temperature is Too Cold for Grass Seed?
Grass seed will not germinate in excessively cold or freezing temperatures. Even cool-season grasses will grow slowly as temperatures plummet and even stop growing altogether. Additionally, it’s very important not to expose new grass seedlings to frost or icy conditions, as this can kill your young grass.
Will Grass Grow in 30 Degree Weather?
Grass will not grow in freezing temperatures. 30℉ (-1℃) is much too cold for grass seed growth of even cool-season varieties. In these temperatures, grass seed will lay dormant until temperatures warm.
- Seed cool-season grasses at least 6 weeks before the average first frost to allow grass to establish itself. Frost and freezing temperatures can kill grass sprouts.
- Seed warm-season grasses at least 90 days before the average first frost. Warm-season grasses thrive in warm weather and are vulnerable to cold snaps.
Will Grass Grow in 40 Degree Weather?
Although some mature cool-season grasses will not enter full dormancy until soil temperatures reach 40℉ (4℃), growth will slow to almost a complete stop by this point. Cool-season grass seed cast in 40-degree weather likely won’t sprout.
Warm-season grasses stop growing entirely by the time temperatures get as low as 55℉ (12℃). You’ll have no luck seeding warm-season grasses in 40-degree weather.
Will Grass Grow in 50 Degree Weather?
A soil temperature of 50℉ (10℃) is the lower limit for seeding cool-season grasses. If daytime temperatures are hovering around 50 degrees, it’s likely that soil temperatures are around 10 degrees colder. Even when seeding cold-resistant grass seeds, it’s best to wait until air temperatures are in the range of 60–75℉ (18–24℃).
What Temperature is Too Hot for Grass Seed?
Although warm-season grasses grow strongly even during hot summer months, many cool-season kinds of grass enter dormancy when temperatures get too high. For this reason, it may not be best to seed grass in mid-summer, depending on the temperature.
Will Grass Grow in 80 Degree Weather?
Warm-season grass seeds will sprout when air temperatures are 70–90℉ (21–32℃), so feel free to seed with Bermuda, centipede, or Zoysia grass at this time.
Cool-season grasses, such as rye and fescue, begin to slow their growth when temperatures top 75 degrees. If daytime temperatures are up to 80, wait until things cool off before seeding cool-season grass.
Will Grass Grow in 90 Degree Weather?
Warm-season grasses will germinate and grow strongly in temperatures up to 90 degrees, so feel free to seed your heat-tolerant grass. Be careful though; temperatures above 90 degrees may put extra stress on young warm-season grass sprouts.
Most cool-season grasses enter dormancy when soil temperatures reach 90 degrees, and cool-season grass seeds won’t germinate when air temperatures are as high as 90.
Grass Seed Germination Temperature
Grass seeds germinate based on the temperature of the soil surrounding them. Cool-season grass seed germinates when soil temperatures are in the range of 50–65℉ (10–18℃). Warm-season grass seed grows strongly in soil temperatures of 65–70℉ (18–21℃).
Because they benefit from cool weather, seed cool-season grasses in fall, 6 weeks before the first average frost. The grass will experience a fall growth spurt, followed by another period of growth in spring, which will help the grass survive the hot summer months.
Seed warm-season grasses in spring. The grass will thrive through the spring and summer months, establishing itself well enough to survive fall and winter temperatures that halt its growth.
