Warm-season grasses are originally from tropical areas of the world and, once established, are able to thrive in scorching sun and high temperatures. They grow most actively when air temperatures are warm, between 70 and 90 degrees F.
The most optimal soil temperature for grass seed planting is from 50-60°F. Conversely, once temperatures reach 77°F and above, it might already be too hot to plant grass seed.
Grass seed needs a warm temperature to germinate and grow. The ideal temperature range for grass seed is between 55-85°F (12-29°C). Anything below 55°F (13°C) will inhibit the growth of your grass seeds, so it's important to keep an eye on the weather forecast when planting.
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.
Spring seeding and dormant seedings won't germinate until soil temperatures are above 50 degrees Fahrenheit. A range of 50-65 degrees is optimal (measured at a depth of 2 inches).
The best time to plant warm-season grass seed is late spring or early summer, or when temperatures hover near 80 degrees or higher in your area. Plant cool-season grass seed in late summer or early fall (when daytime temperatures lower to about 60 to 75 degrees) for best success.
Cool-season grasses go dormant and do not grow during hot weather, when the soil temperature goes above 65 degrees F. Since this is common during the peak summer months, planting cool-season grass seed can result in poor seed germination or even seedling death.
The best month to put grass seed down depends on the type of grass you have. The best time to plant grass seed for cool-season grasses is in early fall or around September. For warm-season grasses, late spring or early summer is the optimal time.
Reinvigorate Your Lawn
By spreading grass seed over your existing lawn, you can thicken up the thin areas, and your lawn will start to look terrific again.
Generally speaking, you can plant grass seed any time of the year, but fall is the best time to seed a lawn with a cool season turfgrass variety. Spring is the best time to plant warm season turfgrass seed. Cool season varieties of grass seed include tall fescue seed, ryegrass seed or even Kentucky bluegrass seed.
Typically, turf type tall fescue is most suited for germination and development when air and soil temperatures average between 60F and 75F.
Extreme heat can quickly kill the grass you've been working hard to maintain all year. Dry and dead grass can also catch fire with ease, which can spread quickly to your home. But with some preventative and corrective lawn care, you can keep your lawn, and therefore your home, healthy and safe.
Grass seed is surface sown, meaning lays and roots on top of the soil, so it does not need to be buried. It's usually broadcast over the ground with a hand or rotary spreader. In order for that seed to sprout, it needs good soil contact, which makes soil quality a major factor in growing a healthy, uniform lawn.
Watering on a hot summer afternoon is a horrible idea. The liquid will evaporate too quickly and may not reach your grass's roots, so heat and irrigation shouldn't go together. Instead, the best time to water grass during summer is in the morning.
It is often recommended that you water your lawn early in the morning, as early as 4 am and no later than 10 am. During extreme heat, watering should be done no later than 7 am.
Whether or not your lawn is dormant, applying fertilizer right now, with the high temperatures we've been having, is not a good idea. Applying either fertilizer or weed killer when it's hot out can damage your lawn. You're better off waiting until later in summer to fertilize.
Seeding to Revive Dead Grass
Seeding a dead lawn is effective but is also the slowest option. You will need to prepare the soil by removing the dead grass and then enriching the soil ahead of laying down new seeds. After the seeds are planted, you will need to fertilize and nurture your grass until it reaches maturity.
Quality grass seed labels include guidance on optimal seeding rates to maximize your results. Don't overdo or cut corners. Too much grass seed causes undue competition for resources such as light, water and nutrients, and grass seedlings struggle as a result. Too little seed leaves lawns thin or bare.
It depends on the type of grass. Kentucky bluegrass has runners that help it spread on its own. But many northern grasses are bunch-type grasses which don't spread, so seeding is needed to fill in bare spots. Perennial ryegrass and fescue are among the non-spreaders.
Use a “mist – lightly water – deeply water” process like this: After seeding and fertilizing, you'll want to keep the top inch of soil moist until the seeds start to germinate (aka sprout). This means misting the area once a day, maybe twice if it's unusually hot out there—but don't let the area get soggy.
A few days before planting your new grass seed, water the entire area about 6-8 inches deep each day. Once you've spread the seed, promptly spend about 5-10 minutes watering the top two inches of soil. The seeded area will need to stay moist so the grass seed doesn't dry out and die.
Water in the early morning and late afternoon, before and after the worst heat of the day. This will allow the water to seep into the soil before evaporating and also helps to conserve water. Avoid watering at night because the water will sit on the grass for too long and promote the growth of mold.
The tables say the optimum temperature range is 40-75°F and the maximum temperature is 85°F. One year, after a frustrating time trying to germinate fall spinach, I took a closer look which revealed that spinach will produce 82% normal seedlings at 59°F, but only 52% at 68°F, and a miserable 28% at 77°F.
Maintaining that delicate balance of soil moisture between too wet and too dry is more challenging during the summer due to the extended drying period. Periods of high temperature, high relative humidity and heavy rains or overwatering can also make new seedings subject to devastating diseases such as Pythium blight.