Grass grows best under cool conditions. Secondly, fertilize the lawn in the fall so that root growth is promoted, not just top growth. After the first two steps are done, the grass will become strong enough to fill in bare areas. The only practical way to tell whether your soil needs lime and fertilizer is to have the it analyzed in a soil testing laboratory. Frequently, just adding a little lime or fertilizer will make a big difference in your lawn's appearance or garden's production.
Soil testing can also determine whether too much lime or fertilizer has been applied.
Excessive lime or fertilizer is not only wasteful, but may decrease growth, give poorer crop quality, cause fertilizer burn and increase the possibility of plant disease. Soil is an extremely variable mixture of mineral and organic matter. The sample you send in for testing must truly represent the area from which you take it. Otherwise, the lime and fertilizer recommendations based on the soil tests will be misleading. Although you can sample any time that is convenient, certain times are better than others.