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The Effects of Mowing on the Growth of Turfgrasses
Combining the Science and the Art of Mowing

Robert L. Green, Ph.D., Plant Science Dept., Cal Poly Pomona

The Effects of Mowing on the Growth of Turfgrasses

Mowing serves cultural and physiological purposes to maintain the quality and function of turfgrasses. Whether the turf is providing a lush patch for children to play or creating recreational areas such as sports fields or putting greens, mowing practices can affect both the aesthetic quality and health of turfgrasses. Robert Green, Ph.D., of Cal Poly Pomona analyzed mowing practices and turfgrasses in a study on the affects of mowing.
Photo: Toro

The Effects of Mowing on the Growth of Turfgrasses

This table measured the effect of mowing height on Tifway Bermuda grass during the study.
Photo: J.B. Beard, Texas A&M Univ.

Mowing is a primary cultural practice on turfgrasses to sustain quality and function, in terms of providing an area that is aesthetically pleasing with uniform appearance. Mowing is also functional by providing recreational areas and a playing surface, such as with a baseball field where bounce of the ball is important or on putting greens where a true putting surface is needed. Mowing is interrelated to other cultural practices, such as irrigation, fertilization, and pesticide applications, along with season and climate.

Basically, mowing removes a portion of shoots including leaves and stems. Physiologically, mowing removes tissue that is involved in the production of carbohydrates through the process of photosynthesis and tissue that is involved in the production of plant hormones, which regulate plant growth. Mowing is a form of plant stress.

Turf Adaptations
Grazing as a form of mowing is not new to turfgrasses. There were concurrent evolutionary developments of grass species and grazing animals beginning during the Eocene epoch, 45 to 55 million years ago. This resulted in natural selection toward those grasses that were morphologically adapted to survive close and continuous defoliation. One adaptation of turfgrasses that allows them to survive close, continuous defoliation is that the major growing point is located at the base of the plant, called the crown. This area is vital to the turfgrass plant because lateral shoots, adventitious roots, and leaves are initiated from this region.

In contrast, broadleaf plants have their major growing point at the plant apex, which would not be well suited to defoliation, though pruning is fine. Another adaptation of turfgrasses is that they spread laterally by tillers, stolons, and rhizomes. This spreading ability is important for turfgrasses to form sods. Tillers are primary lateral shoots that arise from within the basal leaf sheath. Secondary lateral shoots that arise outside the basal leaf sheath and elongate horizontally aboveground are called stolons, while shoots that elongate underground are called rhizomes. Turfgrass species vary by type(s) of lateral stems they possess and resultant growth habits.

The table on page below shows the relative ranking for nine characteristics along with other information for eight common turfgrasses.

Mowing Factors
General factors to consider when describing the effects of mowing include growth habit (how a turfgrass spreads), turfgrass use, and leaf growth rate influenced by climatic and cultural influences. Many cool-season turfgrasses, such as tall fescue and perennial ryegrass, possess a bunch-type growth habit, basically spread by tillers, and require a relatively higher height of cut (HOC).

The Effects of Mowing on the Growth of Turfgrasses

The Relative Ranking For Nine Characteristics For Eight Common Turfgrasses

The Effects of Mowing on the Growth of Turfgrasses

The study examined the effect of mowing height on weed occurrence in a well-established seashore paspalum turf. The right-side plot has been mowed too low, resulting in less dense turf and providing an opportunity for weeds to grow.
Photo: J.B. Beard, Texas A&M Univ.

Many warm-season turfgasses, such as bermudagrass and zoysiagrass, possess a creeping growth habit, spread by stolons and/or rhizomes, and require a lower HOC. In terms of turfgrass use, the mowing requirements (HOC and mowing frequency) are different for a turfgrass used in a park compared to a turfgrass used in a sports field. In terms of leaf growth rate, the mowing requirements of cool-season turfgrasses are different during spring and fall compared to during summer and winter, while the mowing requirements of warm-season turfgrasses are different during the summer compared to during the spring, fall, and winter.

Mowing Effects
Specific effects of mowing include its impact on aboveground and belowground plant growth. Mowing at a lower HOC (within the mowing tolerance range for a particular turfgrass species) generally results in a higher quality: more shoots and leaves per unit area (higher density); narrower leaves (finer texture); more chlorophyll per unit area (greener turf); and smaller tillers (finer texture). It also alters growth: increased shoot growth per unit area; decreased root growth and mass and shallower roots; and decreased rhizome and stolon growth.

Reduced rooting can result in adjusted fertilization and irrigation practices. A relatively lower HOC can also result in reduced traffic and wear tolerance due to: smaller tillers and shoots; increased succulence of shoots; reduced plant biomass per unit area; reduced root biomass; shallower root growth; reduced carbohydrate reserves; and reduced recuperative potential. Generally, turfgrasses are less tolerant when exposed to stress, such as drought, shade, and high temperatures - primarily cool-season turfgrasses. A relatively lower HOC would result in mowing more frequently when following the one-third guide of mowing turfgrasses (removing only one-third of vertical shoot growth at each mowing).

Conversely, a higher HOC would result in mowing less frequently. The one-third guide allows for the least amount of physiological shock due to mowing along with allowing the root system to adapt and potentially increase in size. Mowing at a lower HOC also can result in altering the turfgrass community composition. For example, a lower HOC during the warm season can give Bermuda grass an advantage over tall fescue.

Mowing turfgrass below the mowing tolerance range or mowing too frequently can result in: carbohydrates reserves being depleted; decreased shoot growth; decreased shoot density; decreased sod-forming ability; decreased root mass and depth; turfgrasses prone to weed invasion; and turfgrasses very prone to stress. Mowing turfgrasses above the mowing tolerance range or mowing too infrequently can result in turfgrass that exhibits steaminess, puffiness, and excessive thatch. Turfgrass is also prone to scalping. Moderate mowing practices affect sod formation by stimulating rhizome, stolon, and tiller development.

Proper mowing practices involve adjusting to several factors: HOC is within the mowing tolerance range for the turfgrass being used; climate and stress; shade; applications of irrigation, fertilizer, and pesticides; mowing during turfgrass establishment; and following the one-third guide for mowing and associated adjustments for mowing frequency. However, HOC and mowing frequency are often dictated by practical considerations, such as how the turfgrass is being used and available resources rather than sound agronomics. Lastly, it is good to remember the stresses that turfgrasses are exposed to. Mowing and temperature, along with traffic, can create a difficult situation for plant growth. It would be practical to recall the "art of turfgrass management" with the "science."

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September 20, 2018, 6:23 am PDT

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