What Is The Best Time & Temperature For Grass Seed Germination?

When performing regular lawn maintenance tasks, you must look for weather conditions, such as air and soil temperature. These chores include watering, fertilization, and pesticide treatments. However, that’s not all. The temperature also affects seed germination, and many people ask: what is the best grass seed germination temperature?

Photo Credit The best temperature to sow grass seed depends on the type of grass you are growing.

There is a lot of misunderstanding about the temperature at which grass seeds germinate. Different species of grass prefer different temperatures, and it can often be difficult for the general public to choose the right time to plant grass seed.

Nevertheless, grass seeds generally germinate at temperatures of 55 to 65 degrees Fahrenheit (measured at a soil depth of about 2 inches).

Aside from that, you need to get the timing right and understand your options for perfect seeding success. How can you do that? Read on to find out!

RELATED: How Long Does It Take For The Grass Seeds To Grow? Growing Grass The Easy Way!

Why Do Temperature And Timing Matter?

Why Do Temperature And Timing Matter?

Photo Credit Planting a new lawn will fail if you plant new grass seed at the wrong time or temperature.

If you want to give your grass seeds the best chance of germination and grow as quickly as possible, you should plant them at the right temperature and time, which coincides with their internal growth and life cycle. And lawn grasses, like all other plants, have varying growth cycles and preferences for climate, humidity, air, and soil temperature.

Therefore, you must get the timing and temperature right. Otherwise, you might end up with patchy turf, and you will have to reseed your lawn to fill in the bare spots.

Best Temperature/Time To Plant Warm-Season Grasses

Best Temperature/Time To Plant Warm-Season Grasses

Photo Credit Soil temperatures of 65 °F to 76 °F are ideal for the germination of Bermuda, a warm-season grass.

Warm-season grasses include St. Augustine grass, Centipede grass, Zoysia grass, and Bermuda grass. These grasses are often grown and perform well in southern and western regions of the United States. Sometimes, however, they also grow well in southern transition areas. Nevertheless, as the name suggests, warm-season grasses grow best in warmer temperatures, such as those near the end of spring or at the start of summer.

These times bring warm soil and rain and are an excellent time to plant warm-season grass seeds. However, I recommend waiting until the soil temperatures reach about 65 °F to 70 °F and air temperatures are about 80 degrees Fahrenheit before planting the seeds.

Moreover, as with other plants, the best time to plant warm-season grass seeds will also vary depending on the region. For instance, if you live in a relatively cold area with a risk of first even at the end of the spring, I recommend that you wait until the danger of frost has passed before planting your warm-season grass seeds.

It is because warm-season grasses do not respond well to set or cold soil. Therefore, you must ensure that the ground has dried and warmed up before planting the seeds. However, some people plant warm-season grass seeds later in the summer. 

I do not recommend this as this does not give seedlings enough time to establish themselves before the cold season arrives and the grass goes dormant. However, if you do, ensure that you plant seeds at least 90 days before the first frost.

Best Temperature/Time To Plant Cool-Season Grasses

Best Temperature/Time To Plant Cool-Season Grasses

Photo Credit Creeping bentgrass is a cool-season grass that prefers soil temperatures between 50 °F and 65 °F.

Cool-season grasses include perennial ryegrass, bentgrass, rough bluegrass, and Kentucky bluegrass, to name a few. Cool-season grasses are often planted in the northern regions of the United States. However, they also perform well in transition zones where warm and cool areas meet. Nevertheless, as their name indicates, cool-season grasses germinate best in cool temperatures at the end of summer and the beginning of fall.

These times are characterized by moderate day temperatures and colder night temperatures that provide the best growth conditions for cool-season grass seeds. 

The best soil temperature for cool-season grass seed germination is between 50 and 60 degrees Fahrenheit. The mentioned soil temperature corresponds to air temperatures of about 60 and 75 degrees Fahrenheit. I recommend that you plant your cool-season grass seeds in the early fall when the cool season is about to begin, but the deep soil is still warm from the summer, as cool-season grass seeds still need a bit of warmth to germinate.

However, please remember that the farther north you are, the sooner you will have to sow your seeds, as northernmost regions become cooler earlier. However, do not plant your cool-season grass seeds too late in the fall for successful germination.

I recommend that you plant your seeds at least 90 days before the first expected frost of the season. It will give the seedlings enough time to establish themselves in the ground before the weather and temperatures become too extreme.

If somehow you miss the fall window to plant cool-season grass, the next best time is early spring for the best chances of successful seed germination. During this time, the soil begins warming up after winter. However, it is still cold enough outside to ensure a reasonable germination rate for cool-season grass seeds. Nevertheless, be careful if you plant cool-season grass seeds in the spring. If you sow too late, the hotter temperatures might inhibit germination or negatively influence the growth of seedlings.

Also, there is the chance of late rain or snow. Late rain or snow in the spring can make the soil wet which will cause weed growth decreasing seed germination.

RELATED: How To Plant Grass Seeds On Hard Dirt For Best Results? A Simple & Easy Guide

Soil Vs. Air Temperatures

Soil Vs. Air Temperatures

Photo Credit A soil thermometer is a handy pocket accessory to check the soil temperature before planting.

Reading through this article, you may wonder why we are emphasizing air and soil temperatures separately and whether it matters. Yes, it does. When most people hear the word “temperature,” they think of the local temperature forecast, which might be misleading when planting grass seeds. In other words, you might not want to plant cool-season or warm-season grass seeds based on local weather or temperature forecast alone.

It is because of the insulating properties of the soil surface, which prevents temperature changes in the ground below where grass seeds are usually planted. Therefore, the air or weather forecast temperatures might not accurately represent the soil temperature, and you might end up sowing the grass seeds at the wrong time.

Here are a few factors that can affect soil temperature:

  • Water levels
  • Soil depth
  • Pore space
  • Plant cover
  • Frost

So, how do you measure soil temperatures? It is easy! Here is how to do it.

Calculating Soil Temperature

To start, you will need a soil thermometer. A soil thermometer is inexpensive and can be purchased online or from a local gardening store. Nonetheless, I recommend pushing it about two inches deep into the ground to measure the soil temperature accurately.

Keep the probe in the ground for five minutes, then note the reading. Also, you should take temperature readings in several places in your yard, separately for day and night, and then average them out to see if the temperature is right to plant the grass seeds.

Seed Germination Temperature Chart

To make your work easier, here is a chart showing the ideal temperature for the germination of some commonly used cool-season and warm-season grass seeds.

Grass TypeGermination Temperature
Kentucky Bluegrass59 °F to 86 °F 
Rough Bluegrass68 °F  to 86 °F 
Chewings Fescue69 °F  to 77 °F 
Tall Fescue68 °F  to 86 °F 
Perennial Ryegrass68  °F to 86 °F 
Annual Ryegrass68 °F  to 86 °F 
Bermuda Grass80 °F to 90 °F
St. Augustine Grass80 °F to 100 °F
Zoysia Grass86 °F to 95 °F
Centipede Grass70 °F to 80 °F

What Temperature Is Too Hot For Grass Seed?

What Temperature Is Too Hot For Grass Seed?

Photo Credit Seeds exposed to temperatures above 86 degrees Fahrenheit may fail to germinate.

If you are planting in hot weather, chances are, you are planting warm-season grass. While warm-season grasses grow best in hot weather, they usually enter dormancy if it gets too hot. That is why it might not be a good idea to plant grass seeds when it is too hot.

That said, most warm-season grasses will safely and strongly grow in temperatures up to 90 degrees Fahrenheit. However, if the temperature is above 90 degrees Fahrenheit, I do not recommend planting the seeds as they will have difficulty germinating.

Moreover, aside from the temperature stress on the seeds, you will also face problems keeping the ground moist in extremely hot weather, which is essential for germinating seeds. As for the cool-season grasses, they should not be planted in hot weather.

Most cool-season grasses enter dormancy when soil temperatures hit 90 degrees Fahrenheit. So, growing them at that time would waste effort and resources.

What Temperature Is Too Cold For Grass Seed?

What Temperature Is Too Cold For Grass Seed?

Photo Credit If soil temperature drops below 9 degrees, it can get too cold for regular grass seed to germinate.

If you are planting in cold weather, chances are, you are planting cool-season grass seeds. While cool-season grasses grow best in cool weather, the grass seeds will not germinate if it becomes too cold. Even established grasses stop growing if it gets freezing.

Most cool-season grasses can develop if the soil temperature is above 50 degrees Fahrenheit. However, the temperature is still not suitable for grass seeds. The soil temperature must be above 50 degrees if grass seeds are to germinate successfully.

Moreover, you must ensure that there are no chances of frost in the coming 10 to 12 weeks. If there is frost and seeds are still in the ground, it will stop them from sprouting and kill any seedlings that have not yet established themselves in the soil.

Regarding the warm-season grasses, they should not be planted in cool weather. More of them go dormant when temperatures are this low, and planting warm-season grass seeds in cold or frost would be just a waste of time, resources, and labor.

Dormant Seeding

Earlier, we discussed that grasses go dormant when temperatures are too low or too high. However, even in these extreme temperatures, it is still possible to plant grass seeds. 

It is usually done when homeowners want to reseed their lawns to fix bare patches or thicken up their thin lawns, and it is known as dormant seeding. The idea is to plant grass seeds when the weather is too cold for them to germinate and prepare everything before the favorable temperatures for seed germination and grass growth arrive.

That way, the grass will start growing right at the start of its growth cycle, and you will have a luxurious lawn quicker than if done otherwise and plant grass seeds in favorable temperatures. However, you must ensure that you prepare the soil well and give the seeds everything they need to germinate and grow when the time comes.

RELATED: Pros And Cons of Using Straw To Cover Grass Seed In A Newly Seeded Lawn

Things To Consider When Planting Grass Seeds

Things To Consider When Planting Grass Seeds

Photo Credit The most critical step of site preparation for planting grass seed is to water the area well.

If you get the timing right and sow the grass seeds at the right temperature, they will germinate in no time, and soon you will have a lawn full of grass seedlings. 

However, your job is not done yet. You have to ensure the seedlings establish themselves too. You must keep the ground continuously moist for the first few weeks. However, not so wet that the soil becomes soggy. Depending on the grass, it will take about two to three weeks before the seedlings emerge from the ground and cover the yard.

Then, it is all just a matter of adequate watering and fertilization, and you are good to go.

Frequently Asked Questions (FAQs)

Will grass seeds germinate in 50-degree weather?

Whether or not grass seed will germinate in 50-degree weather depends on the grass you plant. If you are going with cool-season grass seeds, they will start growing at temperatures slightly above 50 degrees. However, most warm-season grass seeds will not.

Will grass seeds germinate at 80 degrees?

Whether or not grass seed will grow at 80 degrees depends on the grass you plant. Most cool-season grasses go dormant when temperatures are this high, and their seeds will not germinate. However, this is the best temperature for most warm-season grass seeds.

Should I water grass seeds if it is cold?

Most lawn experts advise watering your grass until the ground or soil reaches 40 degrees Fahrenheit. In general, as the temperature drops, less water is required. However, you still need to ensure that the ground does not dry, or the seed will fail to germinate.

Will a freeze hurt new grass seeds?

A frost or freeze will not harm grass seeds; they will simply go dormant. However, it can still significantly affect their germination rates. If it gets freezing outside, the seeds will stop growing as the moisture is frozen, which they need to sprout along with warm soil.

Will grass seeds germinate at 90 degrees?

Whether or not grass seed will grow at 90 degrees depends on the grass you plant. If you plant cool-season grass seeds at 90 degrees, they will fail to sprout. However, most warm-season grass seeds will do relatively well in 90-degree weather.

Sources for Further Reading

Turf 101: Optimum temperatures for seed germination | Purdue University Turfgrass Science at Purdue University. Retrieved 28 January 2023, from https://turf.purdue.edu/turf-101-optimum-temperatures-for-seed-germination/

Late Season Establishment Considerations. University of Massachusetts Amherst. (2016). Retrieved 28 January 2023, from https://ag.umass.edu/turf/fact-sheets/late-season-establishment-considerations

Healthy LawnsGrass development: Seed germination rates. Agriculture and Natural Resources, University of California. (2023). Retrieved 28 January 2023, from https://ipm.ucanr.edu/TOOLS/TURF/ESTABLISH/germin.html

Thank you for reading this article on grass seed germination temperature. Also, check out our other articles:

How & When To Water New Grass Seeds For A Perfect Lawn!

How Cold Is Too Cold For Grass Seeds? A Comprehensive Guide

How Long Do Grass Seeds Stay Viable? Does Grass Seed Expire Or Go Bad?