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I .~~III:..'r.lr.1~ Figure 3: Mowing height nffects turf density and root length (adopted from Ferrarn 1.992) ~ I I I I I I I . I I I I I I I Healthy grass How Low to Mow? Mowing height is critically important. Traditional lawncare looks to the close. cropped putting green as the ideal turf. Unfortunately, close mowing can weaken the grass and expose the grass crowns to sunburn. It also exposes the soil to sunlight. which may encourage weed seeds to germinate. Keeping grass taller will actually shade out weeds. reducing them by more than 50% (Alliance forthe Chesapeake Bay 1994),Mowing taller also encourages thicker turf and deep roots (Fig- ure 3). Many grasses spread through stolons (shoots that run along the ground and producea newplanlat the tip) or rhizomes (underground horizontal stems that produce new plants). Since the blade tips contain chemicals that inhibit side shOOlS, mowing can stimulate the growth of sto- lons or rhizomes. However. turf trials at Purdue Uni. vcrsity found the spread of grass varies with mowing height. After 22 weeks, a freshly.sceded lawn that was mowed (0 3/4 inch height covered 42% of its plot. 1n conlra!it. a lawn mowed to 3 inches covered 80% orits plot (Schultz 19H9). Mowing high cncourngcs deep roots hcc.:ausc with more leaf surf<lcc. the grass plants ;.In; ;lhk tu manufacture Inure foou. Researchers at the MJchig~m Agricuhur.:!l Station found. closely cropped grass (I inch mowing hcight) hnJ less rool growth and ...IIIJlll regrowth, as weB as fewer lateral siems (Schultz J l}X9). T...hk J gives gt.:nera] JlIowing heights for ,hfkrcnl grass srecics. Mowed too close Mowing Frequency and Thatch Management Mowing frequency is also important. Mow too much or 100 often, and (he grass can be damaged. To keep the grass healthy. it is recommended that no more than one-third of the leaf be cut at a time. While following the "one~third" rule may mean mowing more fre. quently, it does not necess.arily mean spending more lime behind the mower. This is due to the fact that grass grows at different rates throughout the year. ;mmm.~\\llJ.JI\lm'l'II\\lh~~ When the grass is growing rapidly. it may be necessary to mow twice a week. At other times, mowing twice a month may be sufficient. Lastly, homeowners should learn how to recognize and measure thatch; too much thatch (over 1/2 inCh) is a sign of unhealthy grass, poor maintenance, andJor compacted soil, Thatch is a brown, straw-colored layer between the green grass and the soil. A small thOll.:h layer is actually helpful, it functions like mulch in a Dower-bed to conserve moisture and block weeds. When thatch is deep it may keep water. air and nutri- ents. from rel.lching (he grass roots. Sh..lllow watering, ovcrlcrtili7.ation and close mowing flll can increasc {he: thatch lnyer. Practicing low input lawncare and aeral- ing the soil can prevent exccssive thatch build-up. If thatch nuild-up has occured and sprinkle compost llver (he lawn (a practice called top dn:ssing) and acr;111; to encourage Ihatch decomposilion. :nttmI'G':'l'.o~A>>.."'\UJJ.l\i\\\I""'\"n'~/.'>:o.,~ Keeping grass tall (3 inches or higher) can prevent weed germination and lead to better root growth. Watershed Protection Techniques _ Vol. 2, No.1_ Fall 1995 259