During Lawn Seeding

• If you intend to plant a new lawn from seed, you must fertilize it prior to preparing the soil for seed planting, the Iowa State University Extension reports. You can use a fertilizer that specifically suits your soil, or try a 0-46-0 or 0-20-0 fertilizer according to the manufacturer's directions. You'll also need to apply a starter fertilizer for turfgrass just before you plant the seed, the extension advises.
  
  

Spring

• If you have an established lawn, you should fertilize it in April, The Iowa Gardener website recommends. You can fertilize again in early June to add to the lushness and vivid color of your lawn.
  
  

Fall

• In early fall, you should give your lawn a final application of fertilizer for the growing season. Use a nitrogen fertilizer, and apply 1 to 2 pounds for every 1,000 square feet of yard space, the Iowa State University Extension recommends.