When the weather gets cooler (between 55 and 65 degrees), your lawn starts to concentrate on growing new roots and grass plants. Fall is the time to apply fertilizer so you’ll have strong roots and more shoots in spring.
Most homeowners make sure not to miss the traditional springtime fertilizer application. Early spring applications of nitrogen cause a surge of top growth in the plants. This makes the lawn look nice in the spring, but it actually depletes the plants’ energy reserves causing the grass to weaken and make it less apt to survive periods of stress in the summer. Plus, you are creating more work for yourself with increased mowing.
If you apply fertilizer in late August or early September, you will provide your lawn with adequate nutrition to overcome any summer stresses. In addition, an application of fertilizer in late October or early November will ensure earlier green-up in the spring without stimulating excessive shoot growth.
Look at the diagram above to see why fall is best.