Autumn is the most beneficial time to fertilize your lawn
Grass roots begin storing the nutrients it will need to get through the winter and come up strong the next year. For best results, fertilize once in early fall and once more about 6 to 8 weeks later, around Thanksgiving. Your lawn will look great in the spring, and will be better able to resist weeds and summer stresses.
Fall can also be your most successful seeding time. In fact, over-seeding with grass seed and fertilizer in the fall can make your lawn up to 49% thicker next spring.