They grow best in spring and fall. In early spring, even before the grass starts to green up, the roots break dormancy and begin growing. The combination of long days, cool temperatures and usually adequate moisture produces a flush of growth in the spring. This sometimes makes it challenging just to keep up with mowing. Click for larger view.
Spring is a good time to seed and fertilize bare spots in the lawn from winter damage.
This lush, succulent growth encouraged by spring fertilization makes the plant more susceptible to insects and diseases . Plants with smaller roots are also more vulnerable to drought later in the season. As temperatures warm during summer, growth slows and lawns require mowing less frequently. The combination of warm temperatures and lack of moisture can cause cool-season grasses to go dormant and turn brown during dry summers. In most cases, the grasses haven't died.