After mowing my lawn a couple of weeks ago, I noticed that the tops of the grass blades appeared tattered. This was a clear sign to me that my lawnmower blade needed sharpening. While most gardeners take it for granted, mowing is actually a very important lawn cultural practice, one that not only affects turfgrass appearance, but turfgrass health as well.

Dull mowers tear or shred grass blades rather than cut them. Rotary mowers, which are most commonly used on home lawns, give the lawn a grayish cast when the mower blades are dull. This shredding causes the tips of the mowed leaves to turn brown, and entire leaves may die within a few days. These wounds also provide handy entrance points for certain diseases. A rotary mower depends on impact cutting by a high speed, rotating blade. In general, it is better adapted to a higher cut, and coarser bladed grasses.

Dull or poorly adjusted reel mowers also leave a torn leaf tip or a series of abraded bands across the leaf blade. A reel mower shears the grass with a scissors action and is better for fine bladed grasses and for a low mowing height. You should sharpen both types of blades regularly.

If you mow your grass so short that yellow or brown stem tissue is exposed, you're "scalping" your grass. Scalping can occur when your mower wheel drops into a depression, when the soil surface is uneven, or when you're not mowing frequently enough. Scalping weakens lawns by damaging plant crowns, making them more susceptible to diseases and weed invasion.

You can prevent scalping by mowing regularly, and at the proper height for the grass species. Cool season grasses, such as Kentucky bluegrass, the fescues and ryegrasses, grow the most during spring and autumn, and will require more frequent mowing at those times. A good rule to follow is to mow often enough so that no more than 1/3 of the height of the grass is removed at any one time. For example, if you like your tall fescue at 1-1/2 to 3 inches, mow it when it reaches 2-1/4 to 4-1/2 inches in height. This may mean mowing it twice a week during the spring, but only once every 7 to 10 days during the summer. In the hot Central Valley, the mowing height for cool season grasses should be raised about 1/2 inch from mid-May through September to prevent heat damage. The suggested height for Kentucky bluegrass, red fescue, tall fescue and the ryegrasses is from 1-1/2 to 3 inches.

The warm season grasses, such as bermudagrass, St. Augustine and Zoysia, grow most rapidly in the summer and require frequent mowing at that time. During the winter they require little or no mowing, unless they are overseeded with ryegrass for winter color. They are mowed shorter than the cool season grasses. The suggested mowing height for common bermudagrass is 1 inch; mow dwarf bermudagrasses at 1/2 to 3/4 of an inch; St. Augustine at 1-1/2 to 2 inches.

If either warm or cool season grasses are mowed too low, the lawn may become bleached, shallow-rooted and weakened to the point where it becomes more susceptible to weed invasion and diseases. Mowing too high results in quicker thatch accumulation, especially with the warm season grasses.