Hard-wearing grass such as ryegrass can grow in a matter of 3 to 5 days, but most grasses take 10 days or longer. In most cases, the hardier the grass, the less time it takes for the seeds to start germinating.
Other factors such as water and soil temperatures can affect the rate at which grass grow. Too much water can make the seeds rot, while too little water can make the seeds shrivel up, so growers should use enough water to keep the top 2 inches of soil moist but not squishy. Similarly, cool season grasses need temperatures between 60 and 75 degrees Fahrenheit, and warm season grasses plant well when temperatures are between 80 to 90 degrees.