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Mowing Your Florida Lawn
L. B. McCarty and
J. L. Cisar
Mowing is one of the primary maintenance practices essential for a good
quality lawn. Mowing is the process which creates a lawn rather than a
pasture or a meadow. A smooth, dense turf surface is attained from
frequent and regular cutting of grass leaf blades at a constant height.
The metabolism and appearance of grass are changed by mowing. Immediately
after mowing, plant respiration increases and root growth temporarily
ceases.
The two main components of mowing are cutting height and frequency. Both
of these factors are dependent on the turfgrass species and level of lawn
maintenance. Several other practices involving the use of mowers are also
important in creating a quality lawn.
HEIGHT OF MOWING
The optimum cutting height is determined by the turfgrass growth habit and
leaf width. A grass that spreads horizontally can usually be mowed shorter
than an upright-growing, bunch-type grass. Grasses with narrow blades can
generally be mowed closer than grasses with wide blades. Bermudagrass is
mowed the shortest of the Florida turfgrasses because of its numerous
narrow leaf blades and low growth habit. On the other hand, bahiagrass
needs to be mowed the highest of the Florida turfgrasses to produce a good
quality lawn because of its open, upright growth habit.
Proper mowing height is important in creating a good quality lawn because
it encourages a dense stand of grass plants. A dense turf keeps out weeds
through competition for sunlight and nutrients. A weak thin turf allows
weed seeds to germinate and grow.
Turfgrasses can be mowed at heights other than their optimum if the
management practices are properly altered. Cutting turf below the optimum
height requires production of enough leaf blades to keep a dense green
lawn. To accomplish this, more fertilizer and water need to be applied to
stimulate growth. The disadvantages of low mowing heights are increased
pest problems and faster than normal thatch accumulation. Cutting heights
can get too low, and turf quality will be reduced because of severe
defoliation.
Mowing turf too low
probably ruins more lawns than any other turf management practice.
Cutting turf at the high end of the recommended height range requires a
reduction in the level of management (Table 1). Less water and fertilizer
are required since there are more than enough grass blades to give a good
appearance. Also, by reducing the amount of water applied, plants will
develop more extensive root systems and thatch accumulation will be
reduced. Other advantages of a high cutting height include better pest
tolerance and better survival from environmental stress, such as drought.
Table 1. Suggested mowing practices for Florida lawns.
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FREQUENCY OF
MOWING
The growth rate of the lawn determines how frequently it needs to be
mowed. The growth rate is influenced by weather conditions, level of
management, and grass species. The slowest growth rates occur in the
winter or under low fertility and irrigation, while the fastest growth
rates occur in the summer or under high fertility and watering practices.
Bermudagrass is a rapidly growing grass compared to zoysiagrass.
Low-maintenance grasses like bahiagrass and centipedegrass are frequently
mowed just to remove seedheads rather than to cut leaf blades.
The best recommendation on mowing frequency is to determine the need for
mowing based on growth of the turf. Mow often enough so that no more than
one-third the blade height is removed per mowing. For example, if your St
Augustinegrass lawn is mowed at a height of 3 inches it should be mowed
when it grows to a height of 4 to 4 ½ inches. The grass plant metabolism
is stressed every time the lawn is mowed, but the stress can be minimized
by removing only one-third of the leaf blade at each mowing. It is
important to always leave as much leaf surface as possible for
photosynthesis to provide food for regrowth.
CLIPPINGS REMOVAL
Leaf clippings result from mowing and a common problem is what to do with
them. Contrary to popular belief, clippings do not contribute to the
thatch layer; stems, rhizomes and Stolons produce thatch. On most lawns,
clippings should be returned to help recycle nutrients to our sandy soils.
If the lawn is mowed frequently enough, clippings cause few problems.
Problems arise when turf is mowed infrequently and excess clippings (e.g.,
clumping) result.
MOWING EQUIPMENT
Lawn mowers are available in a wide variety of sizes and styles with
numerous features. The two basic types are the reel mower and the rotary
mower. More recently, mulching, flail, and string mowers have been
introduced. Most mowers can be obtained as push or self-propelled models.
Front, side, and rear clipping discharge models are available. The choice
of mower often depends on personal preference. Points to consider when
purchasing a mower are the size of the lawn, turfgrass species, and level
of lawn maintenance.
Rotary mowers are the most popular because of their low cost, easy
maneuverability, and simple maintenance. A large motor is required to
horizontally turn the blade. The grass blade is cut on impact with the
mower blade. Most rotary mowers cannot mow lower than 1 inch and are best
used for higher mowing heights. The blade needs to be frequently sharpened
and balanced for the best possible cut.
A modification of rotary mowers is mulching mowers. These are designed to
cut leaf blades into very small pieces which are able to fall into the
turf rather than remain on top of the grass. Being so small, these pieces
can decompose quicker than blades cut to traditional size. The mower
blades are designed to create a mild vacuum in the mower deck until the
leaf blades are cut into these small pieces. Mulching mowers do not have
the traditional discharge chute as do most rotary mowers.
Advantages and disadvantages of mulching mowers:
Advantages
1. Clippings are returned to the turf; reduces yard waste and recycles
nutrients to the turf.
2. Mulching avoids contributing to land-fill overuse and eliminates
clipping collection and disposal costs.
Disadvantages
1. Becomes ineffective on wet or tall turf.
2. Blades must be kept sharp.
3. Current models are small and require higher horsepower.
Reel mowers are for highly maintained turf where appearance is
important. Reel mowers cut with a scissor-like action to produce a very
clean, even cut.
They are used at cutting heights of 2 inches or less. The number of blades
needed to produce a smooth, uniform cut will depend on the mowing height.
Generally, as the height is lowered, the greater number of blades needed
on the reel. Sharpening reel mowers is difficult and is best left to a
professional mower repair service.
String mowers are similar to rotary mowers, but the blade has been
replaced with a monofilament line. This is a definite safety feature when
operating the mower in some locations. A high-speed motor is needed in
these mowers to spin the line fast enough for a clean cut. String mowers
are most often used for trimming and hard-to-mow areas.
GOOD MOWING
PRACTICES
Follow these procedures and precautions for safe, good mowing:
Pick up all stones, sticks and other debris before mowing to avoid
damaging the mower or injuring someone with flying objects.
Never mow wet turf
with a rotary mower because clippings can clog the machine. Mow only when
the turf is dry.
Sharpen the mower blade frequently enough to prevent a ragged appearance
to the turf.
Mow in a different direction every time the lawn is cut. This helps
prevent wear patterns, reduces the grain (grass laying over in the same
direction), and reduces
the possibility of scalping.
Do not remove clippings. If clumping occurs, distribute these by re-mowing
or by lightly
raking.
Check your mower every time it is used.
Follow manufacturer’s
recommendations for service and adjustments.
Adjust cutting height by setting the mower on a driveway or sidewalk and
using a ruler to measure the distance between the ground and the blade.
Never fill a hot mower with gasoline.
Always wear heavy leather shoes when mowing the lawn.
Wash mower decks after use to reduce rusting, fungus and weed seed
movement.
Thatch and Its Control in
Florida Lawns
L. B. McCarty and J.
L. Cisar
Thatch is defined as an intermingled layer of dead and living shoots,
stems, and roots that develops between the zone of green vegetation and
the soil surface. Thatch consists of a loosely interwoven collection of
plant matter that imparts a sponginess to the turf. There is a gradual
decrease in organic matter size from the top of the thatch layer to the
bottom of the mat. Mat is very fine, dense, peat-like, and not very
compressible. When excessive (1 inch or more), thatch causes serious
problems in Florida lawn.
WHY IS THATCH A
PROBLEM?
Thatch accumulations are undesirable for a variety of reasons.
Thatch can
restrict water and air movement into the soil.
Dry thatch tends to
repel water rather than allow infiltration, and wet thatch enhances
disease problems. If your lawn has dry spots that are difficult to rewet
(unless you almost flood the areas), these are probably dry thatch spots.
Thick thatch makes
mowing very difficult.
As thatch builds up, mowing height actually increases above the soil line,
and the turf becomes very spongy, allowing the mower to sink into the turf
and scalp the lawn. This results in an uneven appearance and often a
mottled brown and green surface.
Thatch provides an
ideal habitat for insects and disease.
Thatch accumulation
is associated with an increased incidence of brown patch, dollar spot, and
leaf spot diseases as well as sod webworm insects.
A thatch condition
elevates the growing points (crowns), runners (rhizomes and Stolons) and
roots above the soil surface.
As a result, the lawn is prone to winter injury because elevated plant
parts are exposed to greater extremes in temperature. Winter kill of lawns
is often associated with thick thatch layers. Centipedegrass is especially
sensitive to winter kill from their Stolons being elevated and more prone
to cold temperatures in thatch lawns. Heavily thatched lawns also
brown-off quickly (go dormant) following the first exposure to cold
weather, and green-up more slowly in spring.
Thatch can
interrupt and restrict the downward movement of pesticides and fertilizers
into soil.
This reduces the
effectiveness of these materials, making pest control difficult and
producing a non-uniform, erratic response to fertilization.
CAUSES OF THATCH
BUILDUP
Thatch is basically a residue problem that occurs in most turfgrasses.
Thatch buildup has been attributed to numerous factors. Excessive plant
growth (when vegetative production exceeds decay) results in the
accumulation of thatch. Grasses depend upon constant regeneration for
survival, and new growth of creeping grasses covers the old, causing
residue accumulation.
St. Augustinegrass, hybrid Bermudagrass and zoysiagrass may have excessive
thatch accumulation; centipede grass and bahiagrass also form thatch, but
at a slower rate.
Improper management practices can also result in thatch accumulation. Over
fertilizing, overwatering and infrequent mowing are the biggest
contributors to a thatch problem.
In addition, failure to keep the soil environment favorable for bacterial
and fungal growth by pH control, adequate irrigation, and aeration
decreases the rate of decomposition of thatch residues, because these
organisms are responsible for decay of organic matter
Failure to remove clippings after mowing has been cited as a cause of
thatch buildup, but research findings do not support this concept. If
properly mowed, leaf clippings decompose readily and do not cause
thatch.
THATCH CONTROL
Effective control of thatch, requires a combination of several management
practices. These include reducing the buildup rate by reducing plant
growth and increasing microbial decomposition, and by periodic physical
removal by vertical mowing.
Cultural Practices
Fertilizer should be applied as necessary to maintain reasonable growth
and density. This will minimize weed invasion. Excessive succulent growth
not only increases thatch, but also often makes the lawn more susceptible
to pests.
A soil pH of 7.0 is ideal for maximum microbial activity and
decomposition. Liming of acid soils may help increase decomposition of
thatch residues and thus retard buildup. Proper watering can also aid
thatch decomposition. Maximum decomposition occurs if the soil is at
optimum moisture, not too wet or too dry.
Mowing practices can help control thatch buildup. Lawns should always be
mowed at the recommended height and frequency. Thatch seldom increases if
no more than ¼ to 1/3 of the leaf blade is removed at each mowing.
Cultivation and
Soil Topdressing
Periodic cultivation by coring (aerification) and soil
topdressing (application of soil to the turf surface) are standard
maintenance procedures for control of thatch on highly managed turf areas.
Mechanical cultivation removes small plugs of thatch and soil, thus
leaving small holes in the soil that allow penetration by air, water,
fertilizers, and pesticides. It also hastens decomposition by providing a
more favorable environment for microbial activity.
Coring does not
remove substantial amounts of thatch but does provide a more favorable
environment for microbial activity.
Topdressing increases decomposition by bringing soil microbes and moisture
into contact with the thatch. Frequent, light soil topdressings have been
repeatedly shown to be the most effective and consistent method to reduce
thatch.
Thick applications of
topdressing or sand are not recommended and will only compound the problem
by causing a layering effect and possibly increasing disease incidence.
This results in restricted water and air movement, and encourages shallow
root systems. Top dressing materials should be weed and nematode free soil
(sterilized is ideal) of the same type on which the turf is growing.
Topdressing should begin in early spring when temperatures are conducive
for turf growth. Light, frequent topdressing provide quicker results
compared to infrequent, heavier ones. Topdressing rates should not exceed
½ inch per application with lighter rates (e.g., 1/8 to ¼ inch) more
desirable. Topdressing should be repeated until the thatch layer is
reduced or cool temperatures slow or stop turf growth.
MECHANICAL THATCH
REMOVAL
Scalping
Close mowing or scalping is a procedure where the turf is mowed to a much
shorter height than normal in a non-recommended attempt to remove thatch.
However,
scalping is not a
substitute for vertical mowing.
Depending upon which turfgrass you have, scalping height will vary.
Rhizomatous grasses like Bermudagrass and zoysiagrass may be scalped to
the point of removing most of the green vegetation without killing the
turf. Centipedegrass and St. Augustinegrass spread by means of
above-ground runners called stolons. Removing these may kill the turf by
removing all of the stem tissue. Scalping is not recommended for
bahiagrass, Centipedegrass or St. Augustinegrass due to the potential of
turf damage.
Vertical Mowing
The most common method of mechanical thatch removal is the use of a
heavy-duty vertical mower. This specialized piece of equipment has evenly
spaced, knife-like blades, revolving perpendicularly to the turf, that
slice into the thatch to mechanically remove it. This removes both thatch
and mat, and simultaneously cultivates the soil and top-dresses the turf.
It is very important to use proper blade spacing when vertically mowing
different turfgrasses. Use a blade spacing of 1 to 2 inches for
Bermudagrass and zoysiagrass, 2 to 3 inches for Centipedegrass, and 3
inches for bahiagrass and St. Augustinegrass. Because of their underground
rhizomes, zoysiagrass, Bermudagrass, and bahiagrass may be vertically
mowed down to soil level in several directions without killing the lawn.
If all of the aboveground stolons are removed from Centipedegrass and St.
Augustinegrass, these turfgrasses may die. If thatch accumulation exceeds
2 to 3 inches, lawns should be vertically mowed carefully more than once,
but the lawns should be allowed to fully recover between mowings.
Vertical mowing is an effective means of removing thatch, but if not done
properly the grass can be so severely damaged that it may not survive.
Experience with the method and equipment, and knowledge of the type of
grass being renovated are essential. In many cases it may be advantageous
to have a reputable commercial lawn maintenance company remove thatch.
Thatch removal should be considered necessary when thatch thickness
exceeds 1 inch. Frequency of that removal will vary, depending on
intensity of management.
The best time to vertically mow grasses south of Orlando is March through
August; for grasses north of Orlando, the best time is April through July.
Vertical mowing at these times ensures quick recovery since warm-season
grasses grow rapidly during these periods.
After detaching, cleanup is necessary. Thatch removed from an average
sized lawn may fill several pickup trucks. This debris must be raked,
swept or vacuumed, and removed from the lawn. Following cleanup, the lawn
should be conventionally mowed closely to remove further debris. The lawn
should then be thoroughly watered (e.g., ¾ inch of water) to prevent
drying of exposed roots. Approximately one week following dethatching,
nitrogen fertilizer should be applied to encourage turf recovery. Apply 1
pound of actual nitrogen per 1000 square feet in a quick-release soluble
form (e.g., ammonium nitrate or ammonium sulfate). Be sure to irrigate
after nitrogen application to minimize turf burn.
If the preceding steps are followed, excessive thatch can be physically
removed. Such renovation greatly stresses the lawn. Special care will be
needed until the grass completely recovers.
Power Raking
This specialized machine uses evenly spaced, flexible, spring steel tines
that revolve at high speed to strip through turf and loosen debris for
subsequent removal. The machine and procedures are often confused with
vertical mowing. Power raking does not involve a cutting action, as does
vertical mowing. Therefore, it is not a substitute for vertical mowing and
thatch removal, but is used most often to remove a mat layer.
SUMMARY
The following steps should be followed to control thatch formation.
Mow at recommended
height and frequency.
Avoid indiscriminate use of fertilizer. Use minimal amounts of nitrogen,
and soil test for phosphorus and potassium levels.
Maintain a soil
environment conducive to rapid decomposition. This includes adequate
aeration, irrigation, and soil pH control.
Core cultivation (aerification) can help control thatch formation and soil
layering.
Topdressing with sand provides the best biological control of thatch.
Proper timing and rates are necessary to provide the best thatch control
with least chance of disease occurrence.
Use vertical mowers if mechanical removal of thatch becomes necessary.
Follow this with irrigation.
Topdressing
The application of a thin layer of soil to the entire turf surface
(topdressing) to level renovated areas or fill small depressions may be
needed. In addition,
proper topdressing
has been documented by research to be the best overall method of
controlling thatch.
Topdressing provides an ideal habitat for soil microorganisms, that
decompose thatch naturally. Topdress with soil similar to the native soil
on which the turf is growing and use as little as possible to minimize
layering. Never bury turf with topsoil when leveling or filling
depressions since this will kill it. Do not topdress St. Augustinegrass
heavily or conditions favorable for brown patch disease may develop.
Sterilized topsoil should be used to prevent weed seed introduction and
should be screened to remove foreign material such as small twigs and
rocks.
For more information call 850-469-0588
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