"The Grass is Always Greener Over the Septic Tank" proclaims Erma Bombeck in her humorous book by the same title. Your new lawn may be anything but humorous if improper fertilisation burns the grass or worse kills the roots. Prior to seeding, you should have your seedbed soil tested for nitrogen, phosphorous, and potassium and other elements and thoroughly work in a starter or slow release fertiliser that will make up for any deficiencies noted in the soil test. Concentrate on seeding and watering and forget about additional fertiliser until the grass is well sprouted.
Once your lawn has sprouted after about six weeks, an additional feeding of starter fertiliser is appropriate. Starters release slowly with successive watering nutrients to feed young emerging lawn grass. This application should be in an amount indicated for your lawn area as recommended on the bag by the manufacturer.
Avoid homemade fertilisers or hand broadcasting for direct application. An overdose can burn or kill your young grass plants. Use a liquid solution diluted to the proper specifications with a lawn hose spay system or a lawn spreader to distribute your dry fertiliser granules evenly over your lawn. Dry granules must then be watered in, so that the nutrients can reach the roots. Fertilisers are salts and should not be applied in the hottest part of the day. The sun's heat will concentrate the fertiliser and increase the potential for an adverse burn out condition to occur. If you are in doubt, less is better, not more. The growth rate and condition of your lawn will be your prime indicator.
Additional soil tests can be performed, if lawn growth results are proving to be unsatisfactory. If the soil test nutrients are balanced within the acceptable ranges indicated, you will need to look at your soil drainage or for grubs in your root structure, or lawn diseases prevalent in your area.