The very best time to fertilize your lawn is in the spring, when the soil temperature—not the air temperature—reaches 55º Fahrenheit. You'll know when the soil warms up to 55º because the lilacs will begin to blossom and the grass will start growing.
Or, you could purchase a soil thermometer and check the temperature any time. This can mean the first application of lawn fertilizer should take place by about mid-April. So, if you haven't started yet, mark that date.
Lastly, you'll find three numbers printed on the label. These numbers represent the percentage of nitrogen, phosphate, and potassium, respectively, which are the primary nutrients needed to feed your lawn. So, a 20-5-10 bag will have 20 percent nitrogen, 5 percent phosphate, and 10 percent potassium.
Hope this helps! 🌸🌸