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In the lower elevation desert of Arizona, the warm-season turfgrasses (bermudagrass, zoysiagrass, and St. Augustinegrass) become dormant and typically lose their green color during winter. Overseeding bermudagrass with a cool-season grass provides a yearlong green lawn. An oveseeded winter turf provides an aesthetic landscape and functionally provides a recreational turf.
Overseeding is the practice of seeding a cool-season winter grass into the existing bermudagrass lawn prior to it going into dormancy for the winter. The most common winter grass, perennial ryegrass, is planted into the prepared bermudagrass turf and it becomes green from October through May. St. Augustinegrass and zoysiagrass generally are not suited for overseeding.
Timing of overseeding
October is ideal for overseeding when daytime air temperatures are 80-85°F and nighttimes are about 55°F.
Overseeding too early when temperatures are warmer favors bermudagrass and prevents the winter grass from getting established. Later overseedings may be threatened by frost when young seedling grasses may be damaged.
Selecting winter grasses
Annual ryegrass (Lolium multiflorum): Has a light green color, coarse leaves and is fast growing so requires frequent mowing. It's an inexpensive grass for home lawns and commercial landscapes where moderate turf quality is desired.
Perennial ryegrass (Lolium perenne): Has a deep green color, narrow leaves and has improved frost tolerance with better resistance to diseases. It is more expensive than annual ryegrass but produces a better quality winter turf. Persists longer into the spring and competes with bermudagrass that is greening up.
Intermediate ryegrass: A hybrid between perennial and annual ryegrass with some desirable and undesirable qualities of each.
Roughstalk bluegrass (Poa trivialis): Fine-textured grasses commonly used for golf course greens.
Creeping bentgrass (Agrostis stolonifera): Very fine-textured grasses used for golf course greens.
Preparation and care
| 30 days before overseeding | Stop nitrogen fertilization of the bermudagrass lawn |
| 14 days before overseeding | Raise the mowing height 30 – 40% Decrease irrigation by 30% |
| 1 - 3 days before overseeding | Stop watering Mow at the “old” height that was before raising 30-40% Just before overseeding, lower the mowing height another 25 – 30% and leave the clippings as mulch for the overseeded seed |
| Day of overseeding | Use ryegrass seed at 12 to 15 lb/1000 ft2 Apply one-half of the seed by walking in one direction and the other half of the seed by walking in a pattern perpendicular to the first pass |
| 7-10 days after overseeding | Irrigate 3-4 times per day to keep germinating seed moist |
| 14 days after seedling emergence | Fertilize with ammonium phosphate (16-20-0) at 5 lb of product per 1000 ft2 |
| First mowing | When ryegrass height approaches 3 inches |
Amount of seed to use
Use rygrass seed at a rate of 12 to 15 pounds per 1,000 square feet.
- Apply one-half of the seed by walking the spreader in one direction and the other half of the seed by walking in a pattern perpendicular to the first pass
- Drag or lightly rake the seed into the turf to ensure good soil contact or mow seeds into turf with a reel mower
Irrigation and fertilization
Irrigate 3 to 4 times per day for the first 7 to 10 days, until seedlings emerge. Do not allow germinating seed to dry out. When seedlings are established, gradually reduce watering interval to about once a week. The top 6-inches of soil should remain moist. If a long screwdriver easily penetrates the soil to a depth of six inches and comes out damp, no additional irrigation is needed.
At 2 weeks after seedling emergence, fertilize with ammonium phosphate (16-20-0) at 5 lb/1000 ft2. Always water after applying fertilizer. Over fertilizing can increase likelihood of frost damage, disease occurrence, and necessitate extra mowing.
Mowing
Grass should be mowed when dry and with a mower having sharpened blades. Ryegrass should be first mowed when height reaches 2¾ to 3 inches.
- A rotary mower can be set to mow at 2¼ to 2¾ inches
- A reel mower on higher quality turf can mow the turf at 1 to 1½ inches
Spring transition
- Encourage bermudagrass growth by lowering mowing heights by 35% and mow more often
- Apply nitrogen fertilizer weekly at a rate of 0.25 lb/1000 ft2
- Do not stop irrigating. Any drying could slow bermudagrass growth
- Once 80% of the lawn is established as bermudagrass, complete the transition by lightly verticutting to remove the ryegrass, apply 0.25 – 0.50 lb N/1000 ft2 and decrease watering for one week. Repeat the fertilizer application and water cycle to put stress on the ryegrass.
- Aerify bermudagrass during late June, July, through August
- During the summer, bermudagrass should grow for 100 days to establish and grow vigorous roots and rhizomes. After 100 days of active growth, overseeding may be accomplished successfully.