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  MG Manual Reference
Ch. 12, pp. 39 - 43

[Maintenance: irrigation | new lawn | fertilization | renovating | mowing | mowing heights
| dethatching | aeration | weed ]


To maintain a healthy lawn through periods of stress, the soil should have adequate water, air and nutrients in the top 6 to 10 inches. Soils that are hard and compacted impede root growth, which prevents the grass from developing the deep root system that is essential to survive hot, dry periods.
Core aeration is the process of mechanically removing plugs of thatch and soil from the lawn. Aeration opens the soil, helps reduce compaction, improves water infiltration, improves rooting, reduces thatch and acts in many other ways to improve the lawn and to reduce stress.
Power raking is also an effective way to reduce thatch buildup, but it does not have the soil stress alleviation effects of core aeration. These techniques are labor intensive processes that require specialized equipment, but they may be necessary to maintain your lawn in top condition over an extended period of time.
Core cultivation (aerification) can be used to minimize thatch accumulation, to modify its physical characteristics, and to remove certain amounts of thatch. Core cultivation is not as effective as power raking in removing thatch debris, but serves more immediately to reduce soil compaction. Soil cores are either removed or allowed to stay in place after the cultivation process. When left on the surface, cores can be allowed to breakdown and redistribute soil throughout the thatch. Surface cores when dried can be broken up by raking or dragging the lawn with a weighted carpet mat or chain link fence. Cores can be mowed by using a rotary mower at a low travel speed when using a vertical spring blade (dethatch) attachment. This will usually lift up the dry core and pulverize it. The soil within the core modifies the physical structure of the thatch, making it a better growing medium. Soil incorporation also enhances thatch breakdown by improving physical properties of thatch and introducing microorganisms. Core cultivation can be done once a year during the vigorous growing season for bermuda grass to minimize thatch accumulation. Most turfgrasses growing on heavy clay or layered soils require annual cultivation to restrict thatch buildup and more importantly, to relieve soil compaction. Core cultivation is not a substitute for dethatching!
Solid core cultivation is the process by which holes are poked in the ground, but no cores are removed. Rather, the soil is "punched." This is practiced more on highly compacted soils which are high in silt and clay contents. Solid tine aeration can also be practiced on highly compacted surfaces when it is impractical to handle soil core removal on a timely basis. Both core cultivation and solid core aeration result in better root growth. This results from better soil oxygen content and breaking up of the surface soil layer. Do not attempt to core cultivate if the soil is dry, or poor penetration and equipment wear will result.
It is not necessary to add topdressing as an attempt to fill in the holes in most cases. Most soils will respond to a topdressing of organic matter, but it is difficult to fill the holes entirely with an amendment. However, this is a logical time to topdress. Aerification can be done once a year on home lawns. It is best done on warm season grasses during the first third of the summer and in the early fall at higher elevations on Kentucky bluegrass, fescue, and ryegrass lawns (see Maintenance Table).
Low Elevation Fall Overseeding of Bermudagrass

In the low elevation desert valleys (Phoenix, Tucson and Yuma) it is common practice to overseed bermudagrass turf with a suitable cool season winter grass. This provides a green cover when the bermudagrass would otherwise be winter dormant (brown).
The proper procedure for successful overseeding involves (1) proper treatment of the bermudagrass (prior to and during overseeding), (2) proper choice of overseed grass, and (3) proper execution of preparing the seed bed, mulching, post irrigation, fertilizer and mowing practices.
Overseeding should take place when the daytime temperatures are 78-83° maximum and the nighttime low temperatures are 55° or less. This will allow quick germination of the overseed, with little competition from a bermudagrass which should have minimal mechanical disturbance done to it.
Any heavy dethatching should have been done the previous spring or summer. About 4-5 weeks before overseeding, stop fertilizing the lawn completely. At two weeks before overseeding, cut the amount of water normally applied to the lawn by 50-60%. This will trick the grass to store winter food and slow its growth.
For actual overseeding, slowly scalp the lawn by lowering the mowing height 1/4" at a time. Mow 60 to 70% of the grass height off. This will take 3-4 passes with the mower, each at a progressively lower mowing height. Remove the clippings with a bag-catcher lawn mower, or rake them up.
Use either (but not any combination of) perennial ryegrass, annual ryegrass, or hybrid ryegrass. Perennial ryegrasses are by far the best looking, are darker green and have the best turfgrass qualities. Annual ryegrass and the hybrid ryegrass are lighter in color, less dense and require a high mowing height (2.0 inches or higher). These latter two also grow profusely during the spring and require more mowing.
Apply half of the seed, each in two directions, using either a rotary (centrifugal) or drop (gravity) spreader. Seed rates for all three of these ryegrasses should range between 14-18 lbs. per thousand square feet. After seeding, drag a large leaf rake upside down several directions across the lawn. If possible, drag a weighted carpet across the lawn to drive the seed down in the canopy. Follow by topdressing with composted steer manure, or other cost effective weed-free mulch. Apply about 1/4" of manure by use of a wide coal shovel in a slinging motion. Roll the lawn in two directions. Irrigate three times a day at 10:00 am, 12:00 noon and 2:00 pm. Do this until the grass emerges and is about one inch out of the soil. Then irrigate once per day, apply about 1/4" of water. When the grass is 2.0 inches high, mow it to a height of 1 1/2 inches with a sharp bladed mower. The turf must not be wet, or the seedlings may be pulled out. Follow by fertilizing the lawn with 1.0 pound of nitrogen from a quick release source, preferably which has phosphorous also. Water this in.
From this point on, mow the grass when it is 30% higher than the desirable base height. Mow regularly. This will help mature the seedlings into multiple tillered plants. See the mowing height table in this chapter for proper mowing heights.
Spring Transition-Back to Bermudagrass

The return of bermudagrass in the spring is lessened and sometimes a struggle due to the overseed ryegrass. Twenty years ago, simply shortening the mowing heights with more frequent mowings would kill the ryegrass. This is still true for annual ryegrass and the hybrid ryegrass, but not for perennial ryegrass. Spring transition can be a unsightly time for turf. For a better transition, start these practices only when the minimum nighttime temperature is 60ºF or higher for five days in a row. Fertilize the lawn once per week with 1/4 pound of water soluble N. Scalp the lawn slightly every other mowing. Apply regular irrigation amounts as usual. Do not shut off the water for 10_14 days. This will damage the underlying bermudagrass. Keep on this schedule for 3-4 weeks. Then return to the normal base height for the underlying bermudagrass. Mow regularly, as you would for the bermudagrass variety you are growing. Areas with poor transition by mid-summer are probably growing in shaded and/or wet areas, which heavily favor ryegrass.

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