The Lawn care calendar suggests the best time to fertilize. In spring, fertilizer is wasted if it is applied before the soil temperature is above 45 degrees, which is when the grass starts coming out of dormancy. Fertilizer breaks down (becomes available) as air, water, and sun interact with it. If the grass is not capable of using N then it escapes and the fertilizer is wasted.

It is somewhat the same in the heat of the summer. If the plant is in a holding pattern because of the heat then fertilizer is not needed or used so an application then results in waste.

      Spring Late March-Early April use: 10-12-12
      Summer May, June, September use: 25-3-3, plus iron
      Fall November use: 12-8-16, plus iron