Mow high, mow often, and leave the clippings.
Proper mowing gives grass a competitive advantage over weeds and helps keep your lawn healthy. Over the course of the season, mowing is the single most time-consuming lawn-care chore. You may as well do it right!
How high? For a healthy, low-maintenance lawn, set your lawn mower to trim grass to a 3-inch height or higher. This is because the roots underground mirror the shoots on top. The shorter you mow, the smaller the root systems.
Small root systems leave your lawn more vulnerable to drought, insects, and invasive weeds. Short lawns also require more frequent fertilization. Longer grass helps cool the soil surface, reducing water loss from the soil and decreasing competition from warm-season weeds, such as crabgrass.
How often? It depends. Let the grass be your guide, using the One-Third Rule: Never remove more than one-third of the grass blade when you mow. That means if you are cutting your lawn to a 3-inch height, you should mow before the grass is more than 4.5 inches tall. During the spring flush, you may need to mow every 3 to 5 days. During the summer slump, the interval may be two weeks or more. If you are cutting the grass shorter, you will need to mow more often.
When to start? Start mowing in spring when the One-Third Rule says it's time: When the grass reaches 4.5 inches if you are maintaining a 3-inch cut. Stop mowing in fall as growth slows, usually about the time that the daily average temperature falls below 50
° F for a week. Don't leave the grass more than about 4 inches long because it can mat down and encourage snow mold.
What about the clippings? Leave them. They do not cause thatch, contrary to popular belief. (Thatch usually occurs only when turf is excessively fertilized and soil is compacted, cool and moist.) If you follow the One-Third Rule, they won't smother the grass plants. They will quickly dry out and work their way down to the soil surface where earthworms will help incorporate them. Mulching mowers chop clippings finely to speed the process.
The clippings return nutrients to the soil, so you need to fertilize less. They can also cool the soil and help it retain water. Do not blow or leave clippings where they will wash into streets or sewer drains and end up polluting our waterways. Clippings are high in phosphorus, a major non-point source pollutant. If you have a lake, pond, or stream on your property, establish a natural buffer zone between your lawn and the water. Allow the vegetation to grow long in the buffer so that clippings don't get into the stream. The buffer can also filter out other potential pollutants.
Anything else? Keep your lawnmower blades sharp. Dull blades tear the grass instead of cutting it cleanly. The wounds cause the grass to lose more water, increasing irrigation needs or moisture stress, and also leave the plants more vulnerable to diseases.