David M. Kopec, Extension Turfgrass Specialist
Late September in Tucson and mid-October in Casa Grande and Phoenix are ideal times for overseeding bermudagrass lawns with a cool season grass.
The basic steps include: 1) preparing the bermuda for overseeding, 2) providing a seed bed for the overseed, 3) seed placement and mulching, 4) irrigation, fertilizing and mowing.
Preparing the Bermuda for Overseeding
The bermuda should not be heavily fertilized after August 31, since nitrogen will favor more growth and less food storage. Excess fertilization of bermuda in late August can make the bermuda more competetive than it needs to be with the overseed.
Seed Bed Preparation
Severe dethatching should be done in the summer and not at overseeding. Dethatching (power-raking, verticutting) is injurious to the grass and forces stolons and shallow rhizomes to form new plants once they are severed from the base (mother) plant. This weakens the bermuda for winter survival and spring transition.
Homeowners are better off to lightly verticut in at least two directions. After that, the lawn can be scalped. The scalped turf is more open to receive the seed during overseeding. After the scalp, pick up the clippings with a rotary mower and bag them, or cut them in place by mowing the repeatedly.
Seed Placement and Mulching
Annual ryegrass is seeded at the same rate (12-15 lbs.) and should also be applied in two directions. Annual ryegrass is lighter in color, requires higher mowing heights, and is discolored more from repeated frost episodes.
The newly seeded turf can then be topdressed lightly with composted (weed-free) steer manure. Drag or sweep the manure evenly across the turf.
Irrigation, Fertilizing and Mowing
Water the turf 3 times daily at 10:00 a.m., 12:00 noon, and at 2:00 p.m. with just enough water to keep the top 1/2" wet. This is necessary for the seeds to germinate and emerge. Once the seelings reach a height of 1.75 inches, mow the turf at 1.50 inches. then raise the mowing height to a higher base height if desired.
Decrease irrigations to once every two days, putting on 3/8" to 1/2" of water in each irrigation.
SUGGESTED MOWING HEIGHTS FOR DESERT TURFGRASSES
COOPERATIVE EXTENSION UNIVERSITY OF ARIZONA
High Intermediate Low
Maintenance Maintenance Maintenance
| Base | Mow At | Base | Mow At | Base | Mow At | |
| Tifgreen bermuda (419) | 1/4 | 3/8 | --- | --- | 3/8 | 5/8 |
| Tifway bermuda (318) | 1/2 | 3/4 | 3/4 | 1 1/4 | 1 | 1 3/8 |
| Santa Ana bermuda | 3/4 | 1 | 1 1/2 | 1 3/4 | 2 | 2 1/2 |
| Midiron bermuda (EZ turf) | 1 | 1 3/8 | 1 1/2 | 2 | 2 | 2 1/2 |
| Common and other seeded
lawn type bermudas |
1 | 1 3/8 | 1 1/2 | 2 | 2 | 2 1/2 |
| Zoysia Japonica | 1 | 1 3/8 | 1 1/2 | 2 | 2 | 2 1/2 |
| Buffalograss | 1 1/2 | 2 | 2 1/2 | 3 | 3 | 4 |
| Perennial ryegrass | 1/2 | 3/4 | 1 1/4 | 1 3/4 | 2 | 2 1/2 |
| Annual ryegrass | 1 1/2 | 1 7/8 | 1 3/4 | 2 1/4 | 3 | 4 |
| St. Augustine | 1 | 1 3/8 | 1 3/4 | 2 1/4 | 2 1/2 | 3 |
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.