There are a lot of things that you can "wing it" and get by with but, the health of plants is not one of those things. Just throwing a generic fertilizer on a lawn without knowledge of the soil is a waste of time. A lot of times this is the approach that lawn companies go by and while this is an"at best"solution for short term success it often results in being worse off than if you had never done anything in the first place. If you are still having the same problems year after year, more than likely, your soil is in need of testing and analysis. Once the nutrients are fixed it will be extremely beneficial.