To Overseed or Not

Overseeding is the practice of spreading grass seeds directly into standing turf, and this could be done for various reasons – to improve appearance, change the color and thickness, fill bare areas, or to revive an old lawn that has been affected by pests or diseases. One of the most common applications of overseeding is to seed cool-season
winter grass into an existing warm-season grass lawn prior to it going into dormancy for the winter.
Warm season turfgrasses (bermudagrass, zoysiagrass, and St. Augustinegrass) become dormant and typically lose their green color during winter (Figure 1).
Overseeding the warm-season grass provides a green lawn through the winter until springtime, when the warm-season grasses come out of dormancy and resume their
growth.

In the low desert, the ideal time for overseeding is when daytime temperatures are 80-85°F and nighttime temperatures are about 55°F (October – November). Overseeding too early when temperatures are warmer favors bermudagrass and prevents the winter grass from getting established. Later overseeding may be threatened by frost when young seedling grasses may be damaged.
Bermudagrass lawns are commonly overseeded, and the popular choice of winter grass for overseeding is perennial ryegrass. St. Augustinegrass and zoysiagrass are generally not suited for overseeding.
Read more about the process of overseeding winter grasses into summer lawns and the spring transition, in our University of Arizona Cooperative Extension publication.

Overseeding under drought conditions?
Many homeowner associations in Arizona are encouraging residents to skip overseeding this year, to save water and resources. The following links provide information that might help you take a decision:
• The Arizona Municipal Water Users Association (AMWUA) brochure on desert lawn care.
• The Water-Use It Wisely Campaign interactive watering guides and tips to keep overseeding water efficient.

Alternatives to overseeding
Turf colorants such as paints and dyes might serve as a good alternative to overseeding. The colorants keep the dormant grass green through winter, and also help it to come out of dormancy earlier because of solar heat retention, which warms up the soil and roots. Read more about using turf colorants in this article.