Overseeding Bermudagrass Turf
Richard L. Duble, Turfgrass Specialist
Texas Cooperative Extension
Text and images copyright © Richard Duble.
To some, overseeding is a simple operation-just scatter some seed and
wait until they germinate. But to the professional turfgrass manager or
golf course superintendent, whose success depends on the quality of his
product, overseeding is a complex operation that requires preparation, timing
and luck. Unfortunately, knowledge and experience do not always suffice.
Just plain bad luck, usually unfavorable weather conditions, can sometimes
ruin sound procedures.
The objective of a skilled turfgrass manager is to minimize the chance for
failure by proper seedbed preparation, planting adapted grass varieties
at the proper time and careful management during the seedling stage.
Seedbed preparation is just as important for overseeding as for establishment
of a new turf. Perhaps one of the greatest causes of a poor stand of winter
grasses is poor seedbed preparation. Thatch, compacted soils and weeds in
the seedbed can result in seedling diseases and thin stands of grass during
the early stages of overseeding.
Seedbed preparation does not begin two weeks before the date of seeding.
It begins several months prior to seeding. Light vertical mowing during
late summer and fall helps to reduce thatch in bermudagrass turf. Aeration
and topdressing also help control thatch, provide a smooth surface and create
favorable conditions for germination of winter grasses. Timing of each of
these practices is crucial to their success.
Light vertical mowing should begin in midsummer and continue through fall
when bermudagrass growth slows. Frequent vertical mowing so that the effects
are not noticeable after several days is the most successful program to
follow. Vertical mow golf greens weekly and sports fields monthly during
this period. The use of grooming mowers several times each week may substitute
for vertical mowing on golf greens. Infrequent and severe vertical mowing
results in unsightly turf and poor playing surfaces during late summer.
Aeration is also important to seedbed preparation. Late spring and summer
are ideal times to aerify to alleviate compaction, reduce thatch and help
develop a seedbed. Overseeded sites should not be aerated after September
1 because it promotes germination of annual bluegrass. Core aeration within
a month of the date of planting also results in the seed emerging in clumps
rather than in a uniform stand over the site.
Light and frequent topdressing also helps prepare a bermudagrass turf for
overseeding. Topdressing materials may vary between sites, but topdressing
for sand based rootzones should be free of sand particles larger than 1.0
mm in diameter and should contain less than 10% of particles (sand, silt
and clay) below 0.1 mm in diameter. Organic amendments may be added to the
sand to "soften" the mix and increase its moisture and nutrient
retention. Where organic amendments are high in fine sand, silt and clay,
the final mix should not contain more than 10% (by weight) of particles
below 0.1 mm in diameter.
Topdress turf growing on native soils with soil similar to that which exists
at the site. Generally, sandy loam soils are ideal for topdressing such
sites. More important than helping to prepare a seedbed, all of these practices
(vertical mowing, aeration and topdressing) help maintain an attractive,
smooth, resilient surface up to the time of overseeding. Of course, routine
mowing is the unwritten requirement that must go along with the other practices
to maintain fine bermudagrass sports fields and putting surfaces.
Where these cultural practices are followed, there is little else that needs
to be done at the time of overseeding. Disease control prior to the date
of planting is the only other requirement for seedbed preparation. A broad-spectrum
fungicide should be applied one to two weeks prior to planting. The fungicide
application will reduce populations of soilborne disease organisms that
attack seedling grasses. Fungicide treated seed can also be planted to reduce
seedling disease such as Pythium.
Annual Bluegrass Control
Annual bluegrass (Poa annua) can be controlled (but not eliminated)
through cultural practices. If overseeded sites are prepared as previously
described, perennial ryegrasses are the dominant overseeded grasses, planting
date is properly timed and seedling diseases are controlled, annual bluegrass
should not be a serious problem on overseeded sites. On the other hand,
where bermudagrass is severely thinned by vertical mowing immediately prior
to planting, the site is aerated in September or October when annual bluegrass
is germinating and a dense stand of overseeded grasses does not develop
rapidly, annual bluegrass readily invades the winter grasses.
Where turf managers find it necessary to use preemerge herbicides or Rubigan
for annual bluegrass control, they should be applied 60 days prior to the
expected planting date. Preemerge herbicides should not be used on poorly
drained sites or on sites that are moderately shaded. And, when used, herbicides
must be applied uniformly at recommended rates. Rubigan can be used on sites
not suitable for other preemerge products. Ideally two applications of Rubigan
60 days and 30 days before seeding, should be made. Finally, perennial ryegrasses
should be the dominant overseeded grasses planted where preemerge herbicides
are applied prior to seeding. Poa trivialis, fescues and bentgrasses are
more sensitive to preemerge herbicides than the perennial ryegrasses.
The use of preemerge herbicides, proper seedbed preparation and perennial
ryegrasses can effectively eliminate annual bluegrass as a problem on overseeded
The choice of grass varieties for overseeding influences cost, texture,
color, time required for a complete cover, cold tolerance, wear tolerance
and, to some degree, spring transition. But, as for the success of the overseeding
program, the choice of grass varieties is secondary to seedbed preparation.
The most expensive grasses in terms of seed cost per 1,000 sq. ft. are the
perennial ryegrasses. Mixing fescues, bentgrasses and/or Poa trivialis
with the ryegrasses reduces seed costs per 1,000 st. ft. and may improve
the characteristics of the mix in terms of cold tolerance, texture and spring
transition. Perhaps the least expensive overseeding grass that produces
attractive and good playing surfaces is Poa trivialis . The only
weakness of pure stands of Poa trivialis are wear tolerance and annual
Even with higher seed costs, most turfgrass managers prefer the perennial
ryegrasses or mixtures with a high percentage of perennial ryegrass. Their
fast establishment, wear tolerance and competitiveness with annual bluegrass
give the turf manager greater opportunity for success. And, in overseeding
operations, reducing opportunities for failure is important to the manager
and the facility.
Varieties of perennial ryegrass that consistently perform well include Birdie,
Caravelle, Citation, Delray, Derby, Fiesta, Gator, Goalie, Loretta, Manhatten,
Omega, Palmer, Pennant, Pennfine, Prelude, Regal and Yorktown. Grass mixtures
or blends containing perennial ryegrasses have also performed very well.
Poa trivialis in combination with the perennial ryegrass improves
the density, texture and cold tolerance of overseeded sites compared to
ryegrasses alone. Usually, 15 to 20 percent Poa trivialis is required
to make a noticeable difference. The addition of as much as 20 percent Poa
trivialis also reduces the cost of seeding. Varieties of Poa trivialis
that have been consistently outstanding include Sabre, Laser and Cypress.
Fine fescue, bentgrass and bluegrass can also be added to mixtures with
perennial ryegrasses to improve the color, texture and cold tolerance of
overseeded golf greens. Fine fescues are desired because of their very fine,
stiff texture and good wear tolerance. However, the fescues do poorly under
wet conditions and do not persist in hot weather. Improved varieties of
fine fescues that have performed well include Atlanta, Banner, Dawson, Highlight,
Jamestown, Marker, Scarlet, Southport, Vista and Warick.
Creeping bentgrasses are often used in overseeding mixtures because of their
fine putting quality and persistence into early summer. Cobra, Seaside,
Pennfine, Pennlinks, Putter, SR1020, Penneagle, and Emerald creeping bentgrasses
are most often used in overseeding mixtures. A relatively slow rate of establishment
is the major drawback to creeping bentgrasses for overseeding purposes.
Kentucky bluegrasses are used in overseeding mixtures to provide a dark
green color. They also have excellent cold tolerance and retain their green
color under freezing temperatures. However, the Kentucky bluegrasses are
very slow to establish a cover and contribute very little to an overseeding
mixture for the first several months. Varieties of Kentucky bluegrass that
have performed well in overseeding trials include Alble-1, Arista, Baron,
Mystic, Nugget, Pennstar, RAM, Touchdown, Vantage and Victa.
Most golf courses and sports fields are played straight through the overseeding
operation. Thus, it is important to maintain good playing conditions throughout
the period of overseeding. Playing condition is only one reason to begin
preparing for overseeding several months in advance of planting time. Other
reasons include maintaining an attractive appearance and giving the overseeding
operation every opportunity to succeed.
If the site has been prepared as described above (aerated, dethatched and
topdressed during late summer), only regular mowing is necessary immediately
prior to seeding.
Distribute seed in several directions to obtain uniform distribution. Water
lightly for several days to work the seed into the turf. Then, topdress
with sand or a topdressing mixture and smooth with a brush or carpet drag.
Watering is critical during the establishment period. But, avoid overwatering.
Wet, watersoaked sites are not playable and are prone to disease problems
during seedling establishment. On the other hand, the surface must be lightly
watered at frequent intervals to obtain rapid germination. Uniform application
of water is essential to uniform emergence of seedlings. Light watering
two to three times a day for 7 to 10 days is ideal. After seedlings emerge,
watering frequency can be gradually reduced to your regular schedule. Do
not continue the light, frequent irrigation schedule past the germination
period. Thorough irrigation at less frequent intervals is important to leach
salts below the rootzone and to promote root development.
Planting date plays an important role in the success of an overseeding program.
Planting too early increases problems with seedling diseases and with bermudagrass
competition. These two factors can seriously weaken and thin overseeded
turfgrasses. On the other hand, planting too late can prolong the time required
to obtain a complete cover because of low temperatures. The ideal planting
date occurs when soil temperature at the 4-inch depth reaches 72°F
and remains at that temperature or below for 48 hours. Generally, the time
to plant is after bermudagrass has nearly ceased growing, but before freezing
temperatures are expected. A more specific date would be two to three weeks
before the average first frost date. In the northern half of the bermudagrass
belt (North Texas, Oklahoma, Arkansas, Tennessee, North Carolina and the
northern regions of Mississippi, Alabama and Georgia) this date would be
October 1-15. In the southern half of the zone the optimum dates would be
October 15-November 1 and in southern extremes of Texas and Florida, November
1- November 15.
Seeding rate is also important to establishing a fast, dense cover of overseeded
grasses and to competing with annual bluegrass. Low seeding rates result
in thin stands of winter grasses and high populations of annual bluegrass.
On golf greens, perennial ryegrasses should be planted at 30 pounds of pure
live seed per 1,000 sq. ft.; Poa trivialis, at 10 pounds; fine fescues,
at 30 pounds and bentgrass, at 4 pounds. Mixtures of these grasses should
be planted at rates according to the percentage of each grass in the mixture.
For example, an 80-20 mix of perennial ryegrass and Poa trivialis should
be planted at 26 pounds per 1,000 sq. ft. (80% of 30 pounds plus 20% of
10 pounds, or 24 pounds of ryegrass and 2 pounds of Poa).
Sports fields are planted at about 30% of the seeding rate of golf greens.
Sports fields require 8 to 10 pounds of perennial ryegrass per 1,000 sq.
ft. or 3 pounds of Poa trivialis. Only the infield of a baseball field needs
a higher seeding rate. The infield needs about 75% of the seeding rate of
Mowing, watering, fertilization and pest management are all critical to
the successful establishment of newly overseeded winter grasses. Mistakes,
or poor judgement, with any of these practices can lead to poor stands of
winter grasses and heavy infestations of annual bluegrass.
Since play is continuous on newly overseeded golf greens, superintendents
must mow greens daily. Raising the mowing height to -inch and removing grass
catchers for about two weeks after planting will help develop a fast cover.
It is absolutely necessary to keep the mower razor sharp during this period
to prevent pulling up the young seedlings. Daily mowing at -inch during
this time will produce slow, but playable greens. After two weeks the mowing
height can be reduced at 1/32-inch increments to about 3/16-inch four to
six weeks after planting. Daily mowing with sharp mowers is essential throughout
this period. Greens should be mowed when the grass is dry to prevent tracking
seed onto the collars. It may be helpful to lightly water the greens at
daylight to wash dew off the foliage. Not only will that speed drying, but
it may help reduce disease development and leaf tip burning attributed to
Newly overseeded sites should not be kept wet and should not be allowed
to become excessively dry. Close attention to watering is important for
the first several weeks after planting to establish the grass and provide
playable conditions. Avoid late evening watering that keeps grass moist
all night. Diseases can develop and spread rapidly when grass remains moist
Fertilize overseeded sites with a complete fertilizer such as 12-4-8 at
about 1 pound of nitrogen per 1,000 sq. ft. Apply fertilizer immediately
after seeding so as not to "burn" the young seedlings. After seedlings
emerge, light applications of nitrogen will help produce a dense, healthy
stand of grass. Soluble nitrogen sources such as urea or ammonium sulfate
can be applied most effectively as a foliar spray at rates not exceeding
° pound of nitrogen per 1,000 sq. ft. per week. Nitrogen sources with
a low "burn" potential such as Nutralene, IBDU or Milorganite
can be applied in dry applications at rates between ° and 1 pound of
nitrogen per 1,000 sq. ft. Very low rates of soluble nitrogen, such as 2
to 4 ozs. per 1,000 can be applied as a foliar spray along with fungicides.
Seedling diseases such as Pythium and brownpatch must be controlled to maintain
a thick, healthy stand of winter grasses. Application of a preplant fungicide
and the use of treated seed will go a long way toward producing a disease-free
turf. Diseases are much more effectively controlled on a preventative rather
than a curative basis. Once a disease becomes a problem it can set overseeded
grasses back several weeks. Strict attention must be given to spray schedules
for disease prevention for the first several weeks after planting.
Where overseeded fields are covered with tarps during wet conditions, a
fungicide such as Subdue or Aliette must be applied before covering to reduce
Broadleaf weeds such as lawn burweed, chickweed and clover can be controlled
after winter grasses are established. Products such as Trimec, Weedone DPC,
Turflon II Amine and Confront can be used if label directions are followed.
It is important to develop an overseeding schedule well in advance of planting
time. A suggested program might include the following:
- Measure overseeded sites to determine the quantity of seed needed
- Decide on a variety or mixture and order seed in midsummer
- Select several new grasses or mixtures to observe on a practice putting
green or test location
- Vertical mowing schedule (begins during midsummer)
- Aeration (late summer)
- Topdressing (prepare topdressing material ahead of time)
- Preemerge herbicide or Rubigan (optional)
- Preplant fungicide
- Seeding rate (calibrate spreaders)
- Seeding date (soil temperature at 72°F at 4-inch depth)
- During seedling emergence
- After seedling emergence
- Fungicides (Pythium and brownpatch)
- Herbicides (broadleaf weeds)
- Before seeding
- After seeding
Most Common Causes of Failure
- Poor seedbed preparation
- Planting too early (too late)
- Seedling diseases
- Herbicide injury (pre- and post-emerge)
- Overwatering (or excessive rain)
- Fertilizer burn
- Mowing with dull mowers