The million dollar question for many people is "when to fertilize?" To answer this question, you should consider these four factors: climate, grass type, the fertilizer being used, and how you want your lawn to look. For those of us who want our lawn looking its best, then it's a good idea to fertilize your lawn 4-5 times a year. Conversely, even if you don't want a good looking lawn, you should at least fertilize twice a year for your grass's sake. As discussed in the section on grasses, there are two types of grasses: Warm-Season & Cool-Season.