New lawns, be they from seed or sod, can be fertilised in one of two methods and often with combination of both. Fertiliser can be applied before the seed sowing or sodding or after germination and basic root establishment a few weeks after planting. The first year feeding regimen for your new grass lawn thereafter will be dictated in part by which method you employed when planting the lawn.
If Fertilizer Used at Planting
Pre-planting fertilising comes in two forms. First, the soil can be amended with organic matter to enrich it, raise the nutrient content and make it friable and therefore easily penetrated by new tender grass roots. Second, you can apply an even layer of lawn starter formula onto the soil tilling it in lightly. Lawn starter formulas are specially designed not to burn the roots of new seed or sod. These two forms of fertilising are often used in tandem to provide a base layer of nutrient support. Some lawn starter formulas are slow release or long acting. If this is the case, less fertiliser may be needed over the first few months of growth so check out what was applied if anything at planting and use that information to determine when next to fertilise.
If No Starter Fertilizer Was Used at Planting
Apply fertiliser over young new seed and sod grass after installation when the roots have begun to establish themselves into the new soil. This typically means a waiting period of more than two weeks up to four weeks after installation. This prevents the tender new roots from being burnt and prevents the seed and sod from being stressed to produce green tops, and instead all of the energy is devoted to root development. Nitrogen rich fertilisers should be applied to lawns one to four times each year depending on the action of the formula, i.e. whether it is slow release and long acting or not. When using formulations that do require multiple yearly applications, focus the feedings around and during the seasonal growth cycles of your particular grass varietal and your climate.