The best time to fertilize a lawn is during the fall season. At that time of year, the grass is still actively growing and involved in root production. The grass is able to utilize the nutrients from the fertilizer for growth in the fall and yet store nutrients to protect itself from the upcoming harsh winter. The greater the root base in the fall, the greater the potential for the plant to support new vegetative growth that emerges in the spring. Cool season grasses grow most actively in the spring and fall months.
Fertilization is recommended around active growing seasons. Since warm season grasses actively grow in the warm spring, throughout the summer and early fall months, fertilization is recommended during the entire growing season.