Should lawns be fertilized in spring and/or summer? Plantalk's report #1533 discussed this topic.
It is easy to get spring fever as the end of winter approaches. Many people want to begin Gardening and lawn improvements in April. Even retailers encourage us to do so by stacking lawn fertilizer in front of grocery stores and Garden centers. Spring newspaper and radio ads feature lawn care products and fertilizers. This sign of spring is so widespread, many people assume April is the best time to fertilize lawns.
Most Colorado lawns are comprised of cool-season grasses such as Kentucky bluegrass, perennial ryegrass or turf-type tall fescue. These cool-season grasses benefit the most from fall applications of fertilizer, usually sometime in October or November.
Applying a high-nitrogen fertilizer in April may cause grass to grow too fast, before roots can grow to support the lawn. This makes a lawn less tolerant of summer heat.
In most cases, an application of fertilizer in April is not needed when lawns were fertilized the previous fall or clippings are returned to the lawn. If an April application appears to be necessary, apply the fertilizer at a reduced rate. This may be followed by an early June application, a late August application, and the most important application in October or November.
Cool-season grasses should not be given high-nitrogen fertilizers during the heat of summer. It causes excessive, lush growth that requires more frequent mowing and watering, and the lawn becomes more susceptible to insects and diseases.
Conversely, warm-season grasses, such as buffalo grass and blue grama, should be fertilized in late June or July, when most growth occurs.