Mowing near the upper or lower limits will produce different physical characteristics of the grass. Mowing at the lower end will often result in an increase in the growth of the stolons and rhizomes (the runners), resulting in increased turf density and thickness. However, lower mowing reduces the amount of leaf area which decreases photosynthesis and the root mass will usually be decreased. This can reduce the tolerance to foot traffic and other mechanical stress and to heat and water stress, resulting in a brown lawn. Lower mowing is most beneficial during cooler, rainier times of the year.

Raise the height a little during the hot, dry months of mid July through September. Even a small increase in height can produce significant benefits. Higher cuts will provide more leaf area for photosynthesis, resulting in deeper roots and higher resistance to mechanical and environmental stress. Higher mowing height benefits can be seen on the fringe of the golf course putting greens, where the closely mowed green has a more difficult time maintaining high quality in contrast to the higher cut turf on the fringe, which is usually the same species of turf.

The height you use will depend on how often you mow, the mowing height tolerance of your particular type of grass, and its location, use and maintenance intensity level. In shaded areas, for example, raise the mowing height by 30 to 50 percent to compensate for the elongation of the leaf blades under low light. Home lawns should not be cut lower than 1/2 inch. Very low mowing of 3/8 to 1/8 inch should be restricted to golf greens and tee boxes, where special professional care is required.

A reel mower is best on lawns cut at 1 inch or shorter. A reel mower cuts with a shearing action like a pair of scissors, as the multiple blades turn against a stationary bed knife. The reel mower produces a better lawn appearance when the blades are kept sharp and aligned with the bed knife.

However, reel mowers are more expensive than rotary mowers, more difficult to maintain in good working condition and not very maneuverable in corners, tight places and on uneven terrain. They do best on open, level lawns cut at under one inch.

Use rotary mowers on lawns cut at 1 inch or higher. A well-designed rotary mower lifts the grass by creating a suction and gives a uniform crew-cut type look.

A mulching rotary mower keeps the clippings in suspension long enough to re-cut them several times and discharge them directly down into the thatch. The blade must be sharp. If the rotary blade becomes dull it tends to produce a frayed leaf edge that dries out, giving a brown or yellow cast to the lawn.

Rotary mowers cost less than reel mowers and are far more versatile. They handle weeds and thick grass with ease and are much more maneuverable. Disadvantages of the rotary mower are more noise and they tend to wear out faster.

This means the lower you mow, the more often you will mow. If mowing height is 1/2 inch, mow when the grass is 3/4 inch.

With hybrid Bermuda grass you may need to mow every three or four days in the summer. This will be affected by the season, grass grows slower in the winter months.

Vary your mowing pattern to prevent the development of a grain, where the grass runners grow in the direction of mowing cut.

Grain can cause a washboard look to the lawn and increase the chance of scalping if the direction of mowing is suddenly changed.

If you follow the recommended mowing frequency, clippings should not cause a problem and should be left on the lawn. This will recycle the nutrients that would otherwise be lost if clippings are bagged.

As much as 50 percent of the nitrogen fertilizer you put onto the lawn can be retained this way.

Jay Deputy is an education specialist in landscape horticulture and turf at the University of Hawai'i-Manoa Department of Tropical Plant and Soil Sciences, and state administrator for the certified landscape technician program sponsored by the Landscape Industry Council of Hawaii. Send lawn-care or turf questions to deputy@hawaii.edu.