COOL SEASON GRASSES
These grasses grow best during the spring and fall seasons when
it is cool. Cool season grasses struggle during the summer. They
may or may not go dormant during the winter cold. These are mostly
bunch grasses, meaning they grow in bunches and do not have
stolons or rhizomes. The exception is Kentucky bluegrass which
produces rhizomes. Three cool season grasses (perennial ryegrass,
annual ryegrass, and tall fescue) grow by producing shoots in
bunches (tillers) from the base of each plant. Therefore, it is
important to have uniform seed distribution when seeding cool
season grasses to avoid bunchy turf.
Ryegrass, (Lolium species) are one of
three types: perennial ryegrass (L. perenne), annual
ryegrass (L. multiflorum), and hybrid crosses between the
two (L. hybridum). Ryegrasses normally do not grow
year after year in the southwest in the low desert. Therefore
perennial ryegrass is not truly perennial in the low elevation
deserts of the southwest. However, the higher the elevation and
the cooler the temperatures, ryegrass can grow year after year.
Perennial ryegrasses are better adapted to closer mowing
conditions than annual ryegrass, since they have many narrow
leaves on each individual shoot. They also have more shoots per
square inch of turf than annual ryegrass.
Perennial ryegrass can be identified by recognizing
some prominent features. The underside of the leaves are very
shiny and smooth. The leaves have a series of ribs on the surface
which cover the entire leaf surface. In the middle of the leaf
there is a visual depression which forms the midrib.
Perennial ryegrass can be mowed as low as 1/4"
with special management. Moreover, it is adapted to mowing heights
of 3/4" to 1 1/2" with a reel mower. It also is suitable
for mowing heights of 1 1/2" - 2 1/2" using a rotary
mower, which is more common in the landscape industry, and for
Perennial ryegrass is often sold as a blend. A blend is
two or more varieties of the same species of grass. An example of
a perennial ryegrass blend would be 50% Palmer and 50% Prelude.
Each of these are perennial ryegrasses. A mixture is two or more
different species of grass mixed together. A mixture of Kentucky
bluegrass and perennial ryegrass may be available at high
elevation nurseries and garden centers. This is a mixture because
it contains two different species (Kentucky bluegrass and
perennial ryegrass) or more.
Annual ryegrass is lighter in color then perennial
ryegrass. It also has a wider leaf blade, and the mid vein is not
as distinct as that of perennial ryegrass. An enlarged appendage
can be found on annual ryegrass where the leaf attaches to the
grass shoot. It resembles large collars on a dress shirt and is
called an auricle. These auricles wrap around the shoot and are
termed "clasping auricles." These are easily noticed on
annual ryegrass but much less so on perennial ryegrass.
Annual ryegrass does not tolerate frequent close
mowing. It is best adapted to mowing heights of 2 to 3 inches
using a rotary type mower.
A cross between annual ryegrass and perennial ryegrass
has produced a new species of grass called Lolium hybridum.
The intention is to have a grass with better qualities than annual
ryegrass, along with the ease of spring transition of the annual
ryegrass, as well. Most varieties are more upright than the
perennial ryegrasses and are lighter in color. The varieties "Transtar"
and "Froghair" have been sold in Arizona, mostly to golf
courses and landscapers who need to be assured of an easy
transition back to bermudagrass in the early summer.
Annual and perennial ryegrass varieties should never be
mixed together in a seed mixture. The resulting lawn will look
very weedy and have differences in color, texture, and result in
Note that hybrid ryegrass is not a mixture of
annual and perennial ryegrass, but is a separate grass species by
During the fall, bermuda grasses can be over seeded
with ryegrass. Both annual, perennial ryegrasses or the hybrid can
be used. These grasses germinate quickly and have excellent
seedling vigor, thus establishing turfs easily. (For more
information concerning ryegrasses, see Extension Bulletin No.
8652, Over seeding bermuda grasses.)
Tall Fescue, (Festuca arundinaceae) is
a cool season grass which has improved turfgrass qualities. It is
more heat tolerant than the ryegrasses. Other fescue species are
sometimes planted in higher elevation locations. These include:
Sheep fescue, (F. ovata), California fescue, (F.
californica), Red fescue, (F. rubra), and others.
Tall fescue has a deep root system that allows better
survival during drought periods if soil moisture is available.
It's normal range of adaptation does not include the low desert
areas of the southwest. It does have fair shade tolerance, and has
been used to some success in heavily shaded areas, replacing St.
Augustine grass, because of its ease of maintenance, year round
color, and shade tolerance.
Tall fescue has leaves which are about as wide as
annual ryegrass, both of which are wider than those of perennial
ryegrass. The vein pattern is different from the ryegrass as well.
Tall fescue has a flat leaf with many large veins clearly visible
on the leaf surface. It does not have midrib like perennial
ryegrass. Also, hook-like hairs are found on the leaf margins,
pointing toward the leaf tip. These hairs can be felt by running
your thumb and finger along the leaf margin starting from the leaf
tip towards the base. Tall fescue is easily established from seed
in the middle of September in Tucson, and by the first week of
October in Phoenix. In high desert areas planting is best done in
September; the second choice is spring. Fall planting allows
better root development so that the root system is developed
before the hot summer weather. The underlying bermuda or St.
Augustine must be eliminated first, by spraying the actively
growing warm season grass with Round-Up herbicide in the summer.
Tall fescue is not to be used as an overseed on top of
bermudagrass. The result will be a clumpy and irregular lawn.
On prepared ground, tall fescue should be planted at
the seed rate of 8-10 lbs. of seed per 1000 square feet. Increased
seeding rates will result in a weakened lawn condition over time.
Tall fescue is best mowed with a rotary mower at 2.0 or 2.5 inches
as the base height. For shady areas and during the summer months
in the low desert, raise the mowing height to 3.0 inches. Return
to lower mowing height during the following November.
Kentucky bluegrass (KBG), (Poa pratensis)
can be established from either seed or sod. Sometimes
Rough-stalked bluegrass, (Poa trivialis) a finely
textured, bright green perennial grass is mixed in shady lawn
mixtures for its tolerance of shade, and damp soils, along with
creeping red fescue (Festuca rubra). KBG produces rhizomes
but no stolons. These rhizomes help produces a thick dense turf.
Leaf blades have a tip that is shaped like the front of a canoe.
Leaves have a prominent midrib and fine obscure veins. Because KBG
produces only rhizomes and no stolons less thatch is produced than
bermuda grass. Certain varieties of KBG are fairly shade tolerant,
such as `Glade' and `Nugget'. KBG is sometimes sold as seed with
other grasses. These may include fine fescue (for shade tolerance)
and perennial ryegrass (used as a nurse or companion grass). Do
not purchase seed of a KBG mixture which has 10% or more ryegrass
seed in the mixture. KBG are best planted in the fall in high
desert locations or spring in mountain areas like Flagstaff. KBG
will not perform well in low desert areas, and should not be used
in fall overseeding of bermudagrass lawns.