What Is The Most Ideal Grass Seed Germination Temperature? We Help You Figure Out

Kenneth Wilson

Everyone wants a thick, healthy lawn– but the truth is that getting a picturesque dream yard isn't always easy. Aside from ensuring the right equipment, you must provide the perfect timing to plant the grass seed. This includes determining the ideal grass seed germination temperature, so all your effort, time, and money won't waste.

Generally, the ideal temperature for grass seed germination ranges between 9 and 12 degrees. It will also depend on the type of grass you're planting. Cool-season grasses sprout best in the fall, with soil temperatures of 50 to 65 ℉ (or 10 to 18 ℃). This includes bluegrass, Fescue, and rye. Meanwhile, warm-season grasses are best seeded in spring with soil temperatures of 65 to 70℉ (or 18–21℃). This includes Bermuda grass, centipede grass, and Zoysia.

To ensure that your grass seed thrives, you must provide the ideal conditions with the right moisture and warmth for proper germination.

The Best Temperature for Grass Seed Germination

Unfortunately, all your soil preparation and seed sowing activities will be useless if you plant your new grass seed at the wrong time. You will need to consider both seasonal times and ideal temperature ranges as you plant the seed for your lawn. The young seedlings may die or fail to germinate outside these recommended time frames.

Warm-Season and Cool-Season Grasses

Your grass seed will either germinate or stay dormant depending on the soil temperature it has been planted upon. Experts recommend soil temperature mapping to determine whether it's the right time to seed your lawn. But, there are plenty of ways to make a sound judgment of soil temperatures.

Cool-Season Grass Seed

As previously mentioned, cool-season grass germinates best with a soil temperature of 50 to 65 ℉ (or 10 to 18 ℃). This includes the likes of: Bentgrass, Kentucky bluegrass, Tall fescue, Annual ryegrass, and Perennial ryegrass.

Warm-Season Grass Seed

The ideal soil temperature for warm-season grass seed germination is 65 to 70℉ (or 18–21℃). This includes Bermuda grass, centipede grass, and zoysia grass.

Other Factors that Determine the Ideal Grass Seed Germination Temperature

Here are some factors that can determine the temperature of an ideal grass seed germination:

Time of Year

Several homeowners tend to apply grass seed once the yards have been raked thoroughly in the spring. But, spring weather can often be unpredictable. When grass seed fails to germinate during the spring, this is usually because of the wet and cool weather. When grass seed is sown in soil temperatures below 50 degrees Fahrenheit, it may fail to germinate for the next few weeks.

To ensure your soil temperature reaches more than 50 degrees, you must ensure that the outside temperature is 65 degrees (or higher) for at least ten days. In the spring, some areas are prone to frequent rainfalls as well. Heavy rains can only delay your grass seed germination.

Cool-season grass seeds, in particular, grow well during the fall as they experience strong germination and healthy growth before winter. There's a second substantial growth period sometime in the spring. Similarly, warm-season grass seeds benefit when seeded in spring since they will thrive for the summer.

Cool-Season Grasses

  • Ideally seeded during the fall
  • Must be seeded at least six weeks prior to the first frost
  • Enters dormancy when the soil temperature goes below 40℉ (4℃) or rises above 90℉ (32℃).

Warm-Season Grasses

  • To be ideally seeded in the springtime.
  • Must be seeded at least two weeks after the latest spring frost
  • Enters dormancy when the soil temperature goes below 55℉ (12℃)
  • If you live in a region where warm-season grasses enter dormancy in the winter, you may want to overseed it with cool-season grass in the fall to ensure a green lawn for the entire year.

Grass Type

The grass seed type you plan to grow will influence the ideal temperature requirements for its grass seed germination. As such, you need to know whether you are seeding a cool or warm season grass seed. Keep in mind that several commercial grass seeds blend different seed types with varying germination rates. Hence, always check the list of grasses included in your grass seed.

Bermuda Grass

Here are some considerations when seeding with this warm-season grass:

  • Ideally, it must be seeded in the spring
  • Seed when the soil temperature ranges between 65 and 70℉ (or 18 to 21℃)
  • Since this grass is drought-tolerant, it thrives well in arid climates
  • Bermuda is not shade-tolerant. Hence, avoid seeing it on shady lawns
  • It enters dormancy once soil temperatures reach 55℉ (or 12℃).

St. Augustine Grass

This warm-season grass adapts to hot, humid environments. St. Augustine grass is known to spread by above-ground stolons or "runners."

  • Lay new sod in the springtime, with soil temperatures at 65 to 70℉ (18 to 21℃)
  • Unlike Bermuda grass, it is not drought-tolerant and may not survive in arid climates
  • But, it is shade-tolerant, so it can thrive well even without exposure to direct sunlight
  • It becomes dormant once soil temperatures reach 55℉ (or 12℃)

Zoysia Grass

Zoysia is a popular warm-season grass with benefits similar to Bermuda and St. Augustine grass.

  • It must be seeded in the spring
  • Ideally, plant the Zoysia grass once soil temperatures reach 65 to 70℉ (or 18 to 21℃)
  • It can thrive in arid climates and semi-shady areas (able to tolerate light shade)

Kentucky Bluegrass

Kentucky bluegrass is a hardy cool-season grass popular from transitional zones to northern areas of the United States.

  • It 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

Here are some essential considerations when seeding this crowd-favorite cool-season grass:

  • Ideally, it must be seeded in the fall
  • Seed your perennial ryegrass when soil temperatures are 50 to 65℉ (or 10 to 18℃)

Tall Fescue

This next cool-season grass suits residential lawns in the country's cold, northern regions. It is also commonly used as an overseeded seasonal grass in the warmer states.

  • Fescue needs to be seeded in the fall.
  • Seed when soil temperatures range between 50 and 65℉ (or 10 to 18℃).
  • Fescue can be overseeded in the fall on Bermuda, St. Augustine, and Zoysia grass lawns. This grass type retains its green winter through the winter (in the southern regions), so you can still have a green lawn while the warm-season grasses become dormant.

Water & Soil Contact

The grass seed must be planted no more than ½ inch in-depth, with the top 1 inch of the soil kept moist. As long as you follow proper watering with the correct grass seed germination temperatures, achieving the picturesque, lush green lawn you've always wanted is easy!

Final Thoughts

Ensuring your new grass sprouts and develops well won't be difficult as long as you've researched. Before purchasing grass seed, ensure that you know exactly what grass type it is to determine the best time in the year to plant it. If you know the recommended grass seed germination temperature for your new seed, you're well on growing a green, healthy lawn!

Frequently Asked Questions (FAQs)

What temperature does my soil need for seeds to germinate?

Soil temperatures must be above 50 degrees Fahrenheit for spring seeding and dormant seedlings to germinate. A temperature range of 50-65 degrees is ideal (measured at a depth of 2 inches). The germination process will start once reaching this soil temperature.

What temperature is too cold for grass seed?

In extreme cold or freezing temperatures, grass seed will not germinate. Even cool-season grasses will grow slowly or cease growing when temperatures drop. Furthermore, it's important not to expose young grass seedlings to frost or freezing temperatures since this might kill them.

What temperature is too hot for grass seed?

Although warm-season grasses continue to thrive throughout the summer, many cool-season types of grass go dormant when temperatures get too high. As a result, depending on the temperature, seeding grass in the middle of summer may not be the best option.

Why are soil temperatures and air temperatures so different?

Soil serves as an insulator. The pore space is made of water and air, making it a good insulator. These pore spaces either maintain freezing temperatures when they reach a low level or extremely hot when they reach a high level. Because of these insulating properties, transitioning from warm to cold or cold to warm might take a long time.

What factors can affect soil temperature?

It can be affected by number of pore space, depth of the soil, plant cover, frost, and water level.

Kenneth Wilson
June 16, 2022
2terra, Yard & Garden

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

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