when can i fertilize new grass
Starter fertilizers release nutrients slowly, and they will supply nutrients until the grass is established and growing. Begin applying regular lawn fertilizer once the grass has a good root system and is actively growing. This means you'll start fertilizing four to eight weeks after planting.
Apply a starter fertilizer when you're preparing the lawn before planting. Nitrogen (N) and phosphorous (P) are the most important nutrients for new grass, so look for a fertilizer with an N-P-K ratio that has the three numbers the same -- known as a balanced fertilizer -- or is higher in the first two numbers.