Grass seed often begins to germinate in less than a month, which means you should start to see tiny green shoots in the areas you seeded. Establishment of those shoots into a lush, full lawn can take well into the growing season, but it should begin to resemble the lawn you want after you mow it the first time. Planting and caring for the seeds properly is key to help them germinate evenly.
General Germination Times
The basic germination times vary based on variety and the time of year. Cool-season grasses tend to germinate quickly, usually between three and 14 days. Perennial rye grass (Lolium perenne), which thrives in U.S. Department of Agriculture plant hardiness zones 3 through 8, can germinate in as few as five days, although it can take up to 10 days, for example.
Warm-season varieties might take longer, anywhere from five to 30 days. The hardy zoysia grass (Zoysia), for instance, grows in USDA zones 6 through 9 and can take 10 to 21 days to germinate.
Choosing the right time to plant is key in getting your grass established quickly. For most cool-season grasses, the best time to plant is at the end of summer or just as fall begins. This gives the grass time to grow and prepare for the colder winter. Warm-season grasses survive best when planted in late spring so root systems can develop properly before the heat of summer arrives.
To ensure as many of the seeds germinate as quickly as possible, prepare the ground first by removing existing vegetation and debris, followed by tilling or deep raking with a steel garden rake to loosen the soil. This is a good time to add starter fertilizer, such as a 12-25-10 fertilizer spread at a rate of 5 to 8 pounds per 1,000 square feet of lawn.
Spread the seeds evenly, then rake a thin layer of dirt -- about 1/8 inch thick -- over the seeds. A loose layer of a mulch such as straw helps keep the soil moist for the seeds and protects the seeds from wind and birds.
Caring for Seeds
Watering your seeds consistently is key to their survival. The top 1/2 inch of soil must stay moist at all times, which means you must water the seeded areas every day -- sometimes more than once a day, if it's windy or hot outside. Check the soil moisture by poking a hole with your finger to see how deep you must go before your finger comes out dry. Also, stay off the seeded areas as much as possible. Walking over the germinating seeds might compact the soil or push the seeds farther down, making it harder for the shoots to grow effectively.
With proper care, the grass should be tall enough for its first mowing about three to four weeks after you see the shoots appear.
Reasons for Trouble
If you don't see any signs of germination after two weeks for cool-season grasses or four weeks for warm-season varieties, troubleshoot to determine why the seeds aren't growing. Applying weed killers right before or after you plant the seeds might keep them from germinating, for example. You might need to water more or less often; the top layer of soil must stay moist, but if it's completely saturated, grass seed isn't likely to grow. If some areas are holding water and others aren't getting enough, you might need to regrade the ground so the soil is more level before planting new seed.
Soil temperature matters as well. Cool-season grasses germinate best when the soil temperature falls between 50 and 65 degrees Fahrenheit. Warm-season grasses need soil temperatures between 70 and 90 degrees. Adjust your next planting time to fall within the correct soil temperature guidelines.