Watching grass grow

Can you recommend a grass that does not need mowing? It's a question posed perennially to turfgrass professionals, and the answer is "no," unless you desire a meadow instead of a lawn. Although some new turfgrass cultivars do grow to lower maximum heights, they all require some mowing if you wish to maintain them as typical turf.

Fast growth, though it often results in more mowing, is beneficial because it allows turf to become established, to spread and recover quickly from injury. However, growth habit is as important as growth rate, and both affect your choice of species and maintenance practices for a particular site.

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For example, turf that will receive heavy wear, such as a sports field, should consist of types that spread quickly to fill in worn areas. Turf that must be mowed at low heights, putting greens being the extreme, must consist of grasses that tolerate close clipping.

When a turfgrass grows is as important as how fast it grows. Cool-season species grow quickly in spring and fall, but slowly in summer. Warm-season species grow best in hot weather. The conditions that predominate in your region affect your choice of species.

Growth rate factors Turfgrass growth rates involve many variables (see Table 1, page 30). Genetics determines potential growth rates and interacts with the environment and cultural practices to produce the actual growth rate. Conditions being equal, some turfgrasses are inherently (genetically) faster growing than others, even different varieties of the same species. Conversely, the same variety will grow at varying rates in varying conditions.

Grasses grow with one of two basic forms, or habits. Stolons (aboveground spreading stems) and rhizomes (belowground spreading stems) allow grass plants to spread horizontally. Grasses that grow via stolons or rhizomes are termed spreading grasses.

Other grasses lack stolons and rhizomes. These grasses grow in slowly expanding bunches and are termed bunch-type grasses. All major warm-season turfgrasses are spreading types, as are bentgrasses and bluegrasses. Most fescues and ryegrasses are bunch-type species.

Growth habit affects optimal mowing height. Bunch-type grasses grow upright and tend to perform better with higher cutting heights than spreading grasses. Also, finer-leaved grasses (for example, bentgrasses) usually tolerate closer mowing than coarser-leaved grasses (such as tall fescue).

Thus, you'll see putting greens-the most closely mowed turf-usually consist of creeping bentgrass or hybrid bermudagrass, which both are fine-leaved, spreading grasses. St. Augustinegrass, a very coarse-leaved species, and tall fescue, a moderately coarse bunch-type grass, do best when maintained at high mowing heights.

Examine the National Turfgrass Evaluation Program (NTEP) data for more complete information on which grass species and cultivars grow best at various cutting heights. NTEP provides extensive cultivar information on its website at www.ntep.org.

1. Environmental conditions. Environmental conditions play a major role in determining growth rates and also can affect growth habit. Temperature, available moisture and available light are some of the most important environmental factors that affect growth.

* Temperature. Cool-season grasses grow most rapidly in spring, followed by another growth flush in fall. Temperatures of 60 to 75 degrees F promote the greatest development, while above 85 degrees F, growth drops off. An exception is tall fescue, which tolerates heat better than the other cool-season turfgrasses. As long as temperatures are above 40 degrees F, it is possible for cool-season grasses to produce some growth.

Warm-season turfgrasses begin growth at 65 degrees F, thriving best in the 85 to 95-degree F range. Some species can continue to grow at temperatures as high as 110 degrees F. Below 55 degrees F, warm-season grasses generally cease active growth and may go into dormancy.

* Water. As a rule of thumb, most turfgrasses need about 1 inch of water per week in the warm season. During stressful periods, you should increase water by an additional 0.5 to 1.0 inch per week, or consider allowing the grass to go dormant (if it is a species that tolerates dormancy).

Soil quality relates to water availability. Adequate retention of rain or irrigation water is necessary for the best growth rates. Loamy soils provide good water retention while maintaining adequate porosity and aeration. You can amend heavy or sandy soils with organic matter for more optimal soil quality.

* Temperature. Turfgrass grows most rapidly in full sun. In shade, you should raise mowing heights as much as 50 percent to compensate for the more upright growth that grasses produce in low light. This not only improves the appearance; it allows the grass plants to retain more photosynthetic leaf area, a critical factor in shaded areas. Grasses poorly adapted to shade or mown too low will weaken and eventually die.

2. Cultural factors. Cultural factors that affect growth rates include fertilization (rates and timing), pH adjustments, aerification and de-thatching.

Fertilizing, liming, aerating and controlling thatch promote turfgrass growth. Just remember that more is not always better. Fertility should match the needs of the turf. Too much fertility can produce excessive growth that requires frequent mowing and ultimately can weaken the turf. You should lime turf if needed, but first test your soil to find out. Aeration should be a regular part of your maintenance program, but other measures such as vertical mowing or power raking may be necessary as well, depending on the turf.

Mowing within the proper range for each species promotes tillering and yields a denser turf. To a point, higher mowing heights favor turf growth and health. However, excessively high cutting heights may decrease density. Conversely, mowing too low reduces food production and storage, and rooting, which can lead to a host of secondary problems.

In mixed stands, mowing frequency should match the grass with the fastest growth rate. This will not harm the slower growing turfgrass in the mix.

All the above factors-environmental and cultural-interact to affect turfgrass growth rates. Prudent turf managers alter their cultural practices to compensate for less-than-ideal environmental factors. For example, during the heat of the summer, grass growth rates slow. You should then raise mowing heights to reduce stress to the turf and promote rooting. The combination of slow growth and higher mowing heights greatly reduces mowing frequencies of cool-season grasses, compared with spring and fall periods. In drought conditions, growth may cease altogether, sending the plants into dormancy (and seriously cutting into mowing revenues of lawn-care operators).

Table 2 (page 32) lists relative growth rates and habits of major turfgrass species, as well as typical mowing heights and frequencies. Mowing intervals vary according to the height of cut you use and environmental and cultural conditions, so it's hard to be more specific.

Golf course and athletic field managers tend to maintain turf at lower heights, while higher heights are more typical for home lawns and parks. As a general rule, you should choose mowing heights and frequencies to ensure that no more than one-third of the leaf surface is removed in a single mowing. Short mowing heights mean that mowing frequency must increase to adhere to the "one-third rule."

Cool-season turfgrasses * Bluegrasses. Bluegrasses generally spread rapidly, via rhizomes in the case of Kentucky bluegrass or stolons with roughstalk bluegrass. Most grow best when you mow them at heights greater than 1 inch. Cool, moist summers favor these species, with roughstalk bluegrass best suited for wet, shaded conditions. Under extreme heat, the sun-loving Kentucky bluegrass will only grow slowly, even with irrigation.

Some new cultivars of Kentucky bluegrass tolerate cutting as low as 0.5 to 0.75 inch. Breeders have selected these new cultivars for their low growth habit, which allows them to better tolerate closer mowing.

* Fine fescues. The growth rates of fine fescues vary. Creeping red fescue spreads fastest within this group, doing so via rhizomes. Chewings, hard and sheep fescues exhibit bunch-type growth, so they don't spread as much as creeping red fescue.

All fine fescues grow upright, with preferred mowing heights between 1.5 and 2.5 inches. These species grow well in cool summers and high altitudes, as well as cold and arid climates. Fine fescues grow slower than bluegrasses or ryegrasses, allowing for somewhat longer mowing intervals.

Among the cool-season grasses, fine fescues exhibit superior shade tolerance. Nevertheless, in these conditions growth is slower, more upright and more stretched out. Therefore, you should use a higher mowing height for fine fescues in shaded areas.

Unmowed fine fescues produce a meadow-like appearance with the tanned seedheads and unmowed blades. They reach full height by mid-summer. You should mow fescues grown in this manner once or twice a year to stimulate new growth.

Some cultivars of Chewings fescue tolerate mowing as short as 3/16 inch. Because of this ability, these cultivars are occasionally used for overseeding dormant bermudagrass greens.

* Ryegrasses. Annual and perennial ryegrass, known for their rapid germination, spread minimally by tillers, but exhibit rapid vertical growth. Perennial ryegrass mowing heights vary greatly, depending on the cultivar and the site needs. For example, some cultivars with low-growing crowns may tolerate mowing at 0.75 inch or less. In fact, perennial ryegrass is frequently used to overseed dormant bermudagrass putting greens. Mild winters and cool, moist summers favor the most rapid growth with this species.

* Tall fescue. Like perennial ryegrass, tall fescue grows vertically much faster than it spreads horizontally. A few cultivars have short rhizomes that aid horizontal spread. The greatest growth rates occur with moderate winters and warm summers, the conditions to which this species is best adapted. Thus, tall fescue performs well in the Transition Zone. Dwarf or semi-dwarf tall fescue cultivars require less mowing than their non-dwarf counterparts.

* Bentgrasses. Bentgrasses include creeping, colonial and velvet bents. Generally, creeping bentgrass spreads faster than velvet bentgrass, which spreads faster than colonial bentgrass. In my experience, however, velvet bentgrass may be more competitive in the long term than creeping bentgrass.

Stolons are the means of spread for creeping and velvet bentgrass. Weak stolons and rhizomes keep colonial bentgrass's growth at a slower pace, such that it behaves somewhat like bunch-type grass. The more upright growth habit of colonial requires higher mowing heights than are desirable for creeping or velvet bentgrasses, which are well-suited to greens heights. Some of the newer greens-only creeping bentgrasses require mowing heights of 1/8 inch or less to perform optimally.

Warm-season turfgrasses * Bermudagrass. Dense, low-growing bermudagrasses spread rapidly from stolons and rhizomes. Hybrid bermudagrasses grow at lower heights than "common" bermudagrass cultivars. This permits use of the hybrids on close-cut golf greens. Two relatively new bermudagrass cultivars thrive under extremely close mowing. 'FloraDwarf' grows to only about 0.3 inch even when unmowed and will tolerate mowing as low as 3/16 inch. 'TifEagle' requires mowing at least down to 1/8 inch daily, but can be cut as short as 1/16 inch and mowed two to three times daily.

Common bermudagrasses for home lawns grow more upright and necessitate mowing between 1 to 2 inches. Hot, humid summers promote the most rapid growth of bermudagrasses. Growth continues at temperatures as high as 110 degrees F. Shade tolerance is poor, however, and adequate growth is unlikely to occur in less than full sun.

* Buffalograss. Buffalograss tolerates low soil moisture well. This makes it a suitable species for low-maintenance sites. It spreads rapidly by stolons and reaches a maximum height of 4 to 6 inches. This species tolerates lower mowing heights if you wish to give it a finer appearance, and it requires less frequent mowing than bermudagrass.

* Centipedegrass. Centipedegrass grows rather slowly despite having stolons. Even though optimum mowing heights range from 1 to 2 inches, the slow growth keeps mowing frequency to every 10 to 14 days during active growth periods. Unmowed, heights rarely top 4 inches. Centipedegrass continues growing at temperatures as high as 100 degrees F.

* St. Augustinegrass. This species spreads fairly rapidly by stolons. Due to the coarse nature of this grass, preferred mowing heights are 3 to 4 inches, although some of the newer, lower-growing cultivars may be mown as low as 0.75 inch. However, I caution against lower heights because stands become thin as mowing heights decrease. Even cultivars that tolerate lower heights will do better at 1.5 inches or higher.

* Zoysiagrass. Many people associate zoysiagrass with slow growth, which is true of some older cultivars such as 'Meyer'. However, certain newer cultivars exhibit dramatically faster growth rates. With rhizomes and stolons, I have seen some types spread laterally as much as 4 feet from the original plug in one season. Finer-textured zoysiagrasses tend to have relatively low maximum heights, even though some still exhibit vigorous horizontal spread. Zoysiagrasses vary widely in their shade tolerance, but all grow slower in less than full sun. Zoysias continue growing to temperatures of 100 degrees F and, like other warm-season species, go dormant at temperatures less than 55 degrees F. Of all the warm-season grasses, zoysiagrasses and buffalograss survive the coldest winter temperatures, though considerable variation exists among varieties.

Many factors-genetic, environmental and cultural-affect turfgrass growth and development. While some factors are beyond your control, selecting suitable species and cultivars and using proper cultural practices will help you achieve the most vigorous turf possible.

Dr. Bridget Ruemmele is associate professor of turfgrass science at the University of Rhode Island (Kingston, R.I.).

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