Lawn is an area of land, usually around a house, densely covered with grass or other ground cover. For centuries lawns were composed mostly of native grasses and weeds and served mainly as a background for flowers and other ornamentals.
However, with the 20th century trend toward suburban living, especially in the United States, lawns became valued for their own beauty and for their use as recreational areas. They were valued also because they kept the ground fresh and relatively free of dust and mud. Today, lawns are often composed of specially bred grasses and are kept weed-free and luxuriant by periodic mowing, watering, the use of fertilizers, and other practices.
Mowing is a universal requirement of lawns. All grasses should be mowed any time they grow half again as high as the customary lawn height. Infrequent but drastic mowing (scalping) hurts most grasses.
Bent and Bermudagrasses are generally mowed quite short-an inch (25 mm) or less. Traditional bluegrasses, fescues, Bahia, and St. Augustine are mowed taller, usually from 1 1/2 to 3 inches.
As a rule, taller mowing has advantages over shorter mowing: the grass develops more food-producing leaves and deeper root systems.
Lawns of bluegrass and fine fescue, when mowed to no shorter than 2 inches have few weeds, little disease, and endure better where summers are long and hot.
Reel mowers are preferred for low-mowed lawns, whereas rotary mowers are more versatile for higher cut grasses. A heavy-duty mower is recommended for zoysia, an especially tough grass. Ryegrasses have leaf tips that fray easily, so that mower blades must be kept sharp and well adjusted for all lawns containing these grasses.
To look their best, lawns must be watered whenever the soil becomes so dry that the grass begins to wilt. Overzealous watering, however, can encourage moisture-loving weeds, such as Poa annua. In most cases, it is best to let the lawn dry out somewhat between waterings. When watering is needed, enough water should be applied to thoroughly soak the root zone.
The amount of water and the time required for it to soak into the root zone varies according to the type of soil. For example, sandy soil wets quickly but holds little water, while clay soils wet slowly but hold large quantities of water. As a rule, a growing lawn uses about 1 inch of water a week. 1 this moisture is not provided by rain or water held in the root zone, it should be supplied by watering.
All lawns profit from fertilization, northern lawns especially in the autumn, southern lawns especially in the spring and summer.
The newer varieties of grass generally need more fertilization than the older, traditional ones. Bentgrasses and Bermudagrasses, for example, require more feeding than the fescues and Bahia.
Luxurious turfs may require 8 pounds or more actual nitrogen per 1,000 square feet a year. Species requiring little nitrogen, such as the fine fescues, centipede, and Bahia, may look well with only 2 pounds (0.9 kg) of actual nitrogen a year.
Although nitrogen is the main nutrient that spurs growth and promotes good color, the other major plant nutrients- phosphorus and potassium- should also be included in most areas. Fertilizer mixtures, called complete fertilizers, are typically rich in nitrogen with lesser amounts of phosphorus and potassium.
Some weeds can gain a toehold in almost any lawn, but most can be controlled with the use of chemicals.
The growth of annual grasses, such as crabgrass, can be prevented with pre-emergence chemicals spread on the soil before any seeds have sprouted.
Repeated spraying with arsonates can be used to control these weeds after they have sprouted.
There is no effective way of selectively killing perennial grass weeds in a lawn of perennial grasses, but chemicals such as dalapon, amitrole, and paraquat can be used to spot-kill the unwanted vegetation. There are also chemicals available for sterilizing the entire soil bed before a lawn is started.
It should be noted, however, that many chemical herbicides are toxic to animals and can be dangerous to use. They should be used only with great caution, and the instructions on the container should be followed carefully.
Controlling Insect Pests
Lawns may be attacked by several types of insect pests, including grubs, webworms, and chinchbugs. Usually they can be successfully controlled with insecticides, but it is important to select one that is not persistent or harmful to other forms of life. In some instances biological control of lawn insects is feasible. For example, Japanese beetle grubs can be infected with bacteria that cause milky disease.
Birds and other predators are often helpful in keeping a lawn free of troublesome quantities of insects.
Dense, heavily fertilized lawn grasses, especially bentgrasses and Bermudagrasses, may build up a layer of old vegetation called thatch. Powered thinning machines can usually reduce the thatch. Machines that punch holes in the soil will also help control thatch and on heavily trodden ground may also be beneficial by allowing air and water to reach the root zone.
Unless absolutely necessary, rolling should be avoided since it tends to compact the soil. If the surface is uneven it is best to level it with about a quarter inch (6 mm) of topdressing containing weed-free soil. Topdressing helps promote decay of thatch and is often used on golf greens and other well-kept turfs.