Berks County Cooperative Extension -

TURFGRASS - MOWING

Mowing grass generally.

On one level, cutting turfgrass may be viewed as regularly recurring warm weather chore. Considered from another level, proper mowing practices - and an appropriate fertilization program - are essential to maintaining a healthy, visually engaging lawn. Planning a mowing program involves taking into account the following factors:

Height of cut.
Frequency of cut.
Mowing equipment.
Disposition of clippings.

Cutting height.

While an extended discussion of botany is beyond the scope of this page, a very basic understanding of photosynthesis may serve to illustrate the need to consider cutting height. Plants, unlike animals, have the ability to manufacture their own food. The food manufacturing process, called photosynthesis, requires energy from sunlight, carbon dioxide from the atmosphere and moisture from the soil. If any of these ingredients is temporarily unavailable, food production will cease. If any ingredient becomes permanently unavailable, the plant will die.

Turfgrass must have an adequate leaf (blade) surface for photosynthesis to occur. While the measure of adequate leaf surface varies among turfgrass species, it is important to remember that most turfgrass will suffer interruption of the food manufacturing process if it is cut too short. Suggested cutting heights for the cool-season turfgrasses commonly planted in Pennsylvania are set forth in the following table:

Species	Mowing height (inches)
Kentucky bluegrass	1.5 to 2.5
Perennial ryegrass	1.5 to 2.0
Fine fescues	2.0 to 2.5
Tall fescues	2.0 to 3.0

Cutting frequency.

When mowing grass, the general rule is to remove no more than one-third of leaf tissue. Infrequent mowing of rapidly growing grass removes too much leaf tissue, resulting in psysiological trauma to the grass and reduction in the photosynthesis (food making) process. In the spring when conditions for leaf growth are ideal, it may be necessary to cut turfgrass more frequently than once a week. If a mulching mower is used and the clippings are returned to the lawn, infrequent mowing leaves behind clumps and trails of clippings that encourage disease development and invite insects. If heavy accumulations of clippings result from infrequent mowing, simply allow the clumps to dry, collect them and use them as mulch in the vegetable garden or elsewhere. Where, however, the lawn has been treated with a broadleaf weed killer in advance of mowing, the clippings should not be used as mulch for three or four months to allow for dissipation of the herbicide.

Mowing equipment.

While reel-type mowers produce a finer cut than rotary style mowers, rotary mowers will produce an acceptable cut if the blades are properly adjusted and kept sharp. Dull blades may cause damage to the lawn. Mulching model rotary mowers are designed to reduce the size of the the grass leaf to aid in decomposition. It is, however, not necessary to purchase a mulching mower to recycle clippings. Acceptable results may be obtained using an ordinary lawn mower.

Disposition of grass clippings.

While many homeowners remain committed to collecting (bagging) grass clippings and placing them in the trash stream, there are undisputed advantages to recycling or returning clippings to the lawn. Recycling conserves expensive and dwindling landfill space. Returning clippings to the lawn adds nitrogen to the soil, decreasing the amount of fertilizer required to sustain a healthy lawn. Recycling is less labor intensive than bagging clippings.

Some homeowners are concerned that returning clippings to the lawn will contribute to thatch buildup. If proper mowing techniques are followed, returning the clippings to the lawn will not cause or add to an accumulation of thatch since the clippings decompose rapidly.

Sources: The Penn State Master Gardener Manual
Lansdschoot, Leave Grass Clippings On Lawn, http://www.aginfo.psu.edu/News/march98/grassclip.html, November 27, 1999
Document created: 15 December 1999; Revised: 3 March 2001