Even if you are somewhat cavalier in the care of your lawn, you'll probably be able to maintain it fairly well if you water regularly, then follow this one rule: never mow off more than the topmost third of a blade of grass at one time. Even if the lawn is overgrown, mow off just a third; then wait a few days and mow another third. Because each blade of grass provides food for the entire plant, continual scalping will compromise the health of the lawn. Some of its roots may die; it will be less able to withstand extremes of temperature, lack of water, and incursions by pests and diseases.

The optimum heights of various grasses differ. Under normal conditions, these heights are:

• Common Bermuda, hybrid Bermuda, and colonial bent grass: 1/2 to 1 inch

• Zoysia and centipede: 1 to 2 inches

• Perennial rye and St. Augustine: 1 1/2 to 2 inches

• Fine fescue: 1 1/2 to 2 1/2 inches

• Bahia, blue grass, and tall fescue: 2 to 3 inches

• Buffalo grass: 2 to 4 inches

Warm-season grasses grow fastest in hot weather, cool-season grasses in spring. At the peak of the growing season, mowing may be needed more than once a week. At other times of year, every 2 weeks or even once a month may be enough.

LAWN MOWERS

Hand-pushed mowers were once the only type of mower sold. The original models were cumbersome, and their popularity declined with the advent of self-propelled gasoline and electric mowers, which are easier to use: you just walk along behind them, guiding their direction. But gas mowers--like car engines--require regular maintenance, can be fussy about starting, and spew fumes into the air. And the standard electric mowers, though fume-free, can cause problems too: you need to have an outdoor outlet and, in order to mow a large yard, a very long cord.

In recent years, improvements have been made in all types of mowers. The new hand-pushed types, suitable for small to medium-size lawns, are more compact and lighter in weight than their predecessors; many can easily be carried in one hand. Their blades cut cleaner and stay sharper longer than those of self-propelled mowers. (Most models have four or seven blades; a four-bladed mower is a good choice for most home lawns, while a seven-bladed model will cut a bent-grass lawn to putting-green perfection.) And, of course, these mowers don't fill the air with gas fumes.

The pollution problem is certainly one drawback of gas mowers: it has been postulated that they contribute significantly to poor air quality, and in many cities gardeners are asked not to use them on "spare the air" or "ozone action" days. Still, the newest gasoline mowers offer an improvement over older types. The simple two-cycle kinds have more efficient engines and require less mechanical know-how to stay in running order. Many are fairly light and small, good choices for maintaining a medium to large lawn.

Electric mowers have changed dramatically. They still offer self-propelled power without gas fumes or noise, but the cord is gone, replaced by a battery with enough power to cut most lawns on a single charge.

Most gasoline and electric mowers include so-called mulching mowers that chop the cut grass blades into tiny pieces and deposit them back on the lawn. While it's always a good idea to leave grass clippings on the lawn--they decompose and return nutrients to the soil--mulching mowers result in a neater look (since the clippings are so fine) and speed up the decomposition process.

Mower blades should be sharpened at least once a year, more frequently if the grass begins to look chewed rather than sharply cut.

EDGING

Edging a lawn can take as much time as mowing it. Concrete or brick mowing strips reduce the need for edging; where such a design isn't feasible, hand-held shears are effective for edging small areas. For larger lawns, however, battery-operated or gas-powered edgers are more efficient.

Some gardeners use string trimmers ("weed whips") for edging lawns. These are an unwise choice for edging around large shrubs or trees, since the nylon string can easily whip into the bark and damage it badly. They're also risky around annual and perennial beds: angle the trimmer the wrong way for even a split second and you'll decapitate your plants.