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Regardless of how carefully you have prepared the soil and sown your seed, planting a new lawn can fail if you elect to plant new grass seed at the wrong time of the year.
There are both seasonal times and temperature ranges that must be taken into consideration when deciding when to plant your seed. Planting outside of these recommended time frames will frequently result in failure to germinate or death to young seedlings.
Here is a nice, easy to read grass seed temperature germination chart that I found on Old School Lawn Service:
Time of Year
Most homeowners automatically apply grass seed in the spring once their yards have been thoroughly raked and bald patches of dirt have been discovered.
The problem is that spring weather is often unpredictable, even within the same area.
The primary reason why grass seed fails to germinate in the spring is because of the wet and cool weather. Grass seed that is sown in soil temperatures below 50 degrees Fahrenheit can fail to germinate for many weeks – if at all.
In order for soil temperatures to reach above 50 degrees, the outside temperature must 65 degrees or higher for 10 consecutive days.
Springtime is notoriously rainy as well. Although water is required for grass seed to germinate, there can be too much of a good thing. Heavy springtime rains can delay grass seed germination.
The species of grass seed you wish to grow will also have an effect on the temperature required for the grass seed to germinate.
Cool Season Grasses
For example, cool season grasses are should be planted in the early fall. These grasses grow best when the daytime temperatures range from 60 to 75 degrees. Within this temperature range, soil temperatures will usually be between 50 and 70 degrees, which is ideal for germination.
Although cool season grasses like cool temperatures, it is important to plant them early in the fall to ensure that their root systems have time to mature before the first frost hits.
The fall is the best time to plant cool season grasses.
Warm Season Grasses
Warm season grasses are generally planted in the U.S.D.A.’s hardiness zones 8 through 10.
In order for these plants to successfully germinate, daytime temperatures must average around 80 degrees Fahrenheit; however, daytime temperatures do not always serve as the best indicator. If evening temperatures are averaging 70 degrees, then it is more than likely that the soil temps will around the same.
The springtime is the best time for planting warm grass seed.
If spring is particularly cool in your area, wait until early summer to plant warm season grasses. Ideally, they should be planted in the full sun to ensure proper root establishment.
Don’t forget that seeds rely on both warmth and moisture to swell and sprout.
Don’t Forget Water & Soil Contact
Grass seed should be planted at no more than a ½ inch in depth, and the top 1 inch of soil should be kept moist.
With proper watering and the correct temperatures, you will soon have the lush green lawn you have always desired.