Mowing is a violent physical removal of living tissue, causing a severe shock to the grass plant. The shock results primarily from a reduction of the food available to the plant. Grass lives mostly on food manufactured in its leaves rather than drawn up from the roots.
Through the process of photosynthesis, the blades use energy from sunlight to combine carbon, oxygen, and hydrogen into sugar, starches, and fibers. The sugars then combine with soil minerals to make proteins, plant oils, and fat. The soil minerals make up only 5 percent of the solid material in the grass plant. The balance is the carbon, hydrogen, and oxygen which the blades take from the air. Cut those blades, and you reduce the ability of the plant to manufacture food.
The important point to remember is food manufactured by the leaves is used for both top and root growth. The longer the top growth, the deeper the roots, the shorter you cut your lawn, the less the root will grow. This is very important to the health of your lawn. A plant with deep roots will be better able to withstand drought and fight off diseases. Strong roots also serve to store food that has been manufactured in the leaves. Every time you mow, the grass is torn, and if the mower blade is dull, the mowing creates ports of entry for disease.
Mowing also has its good points and if properly done, it can make a lawn thicker and more weed resistant. Mowing prevents the grass from seeding, but many grasses respond by tillering through the spread of stolans and rhizomes, thus a thicker lawn. Mowing encourages tillering because the blade tips contain chemicals that inhibit the growth of side shoots. This works much like pruning a plant, pinch off the terminal bud, and side shoots grow. Studies show that mowing lawns high not only reduces exposed ground surface greatly discouraging weed seeds from germinating, but promotes a longer root system, less susceptibility to insect invasion, and helps to hold moisture. An important part in a good organic program starts with mowing your lawn at a height of 3 ½ inches and 2 ½ inches for the last cutting in fall to discourage snow mold.
Grass clippings are a good source of free fertilizer and an important part of a low maintenance fertilizing schedule providing up to 1/3 of the nitrogen needed by a lawn. Research has found that clippings begin to decompose within a week after cutting (with nitrogen from the clippings showing up in new the growth), this should dispel the fear that leaving the clippings on the lawn will lead to thatch. Therefore an organic managed lawn will recycle grass clippings back on the lawn. Chemical fertilizers slow the activity of decomposers- earthworms, bacteria, fungi, and other microorganisms- and can stall the breakdown of clippings causing thatch.
Follow the basic rule of not cutting more that 1/3 of the height of the lawn, approximately 5 to 7 days in spring and up to 14 days during periods of summer drought .Grass cutting will leave a clean lawn year round as long as you follow this rule. During early spring periods of extreme wet, the lawn might not be cut as clean as normal.