The lime applications depend on the type of soil that is present, number of hardwood trees in the lawn, if the leaves are mulched or picked up, how long the leaves are left on the lawn, and if any fertilizer is being used. These things will determine how fast the ph changes. In Tn. our soil is very heavy clay. We will lime in Spring and Fall to keep the ph where it needs to be. Remember, you can't put down too much lime at once since the soil cannot use a heavy application, so repeat applications are better for the soil than one heavy application. Also, of all of the nutrients and additives you put on the soil, lime will leach out faster than the others.
An easy way to solve the problem of does it need it, get a ph tester and keep it in your truck. We sell tons of lime jobs while giving lawn spray applications. Just stick the tester in the soil when you start talking to the prospect, when your done giving the estimate for spraying pull the tester out and "buy the way Ms., the ph of your soil is one point low, it will require X pounds of lime to correct it, would you like to add that while we are here?
Don't sell what they don't need, just take care of the lawn's needs and you will be taken care of.
Greg Pierce, CTP