Lawns are a biological system
comprising soil, fungi, bacteria, invertebrates and nutrients required
to support a monoculture of a desired plant species, usually a grass.
They provide an amenity area, a nitrogen-rich leaf litter for composting,
and a firm area underfoot for safe playing.
This information provides an understanding of the principles of
lawn care and information required to maintain lawns in a green,
firm and hardwearing condition. Regular maintenance of established
lawns is required to maintain a monoculture of one particular grass
cultivar in the face of competition against weed species. Frequent
tasks are mowing and watering. Annual tasks include fertilising,
controlling moss and other weeds, pests and diseases.
New Zealand scientists have had considerable involvement in the
development of turf-type perennial ryegrass. The first true turf-type
perennial ryegrass cultivars were bred in the USA in 1975. At that
time the New Zealand Government was concerned that wholesale importation
of inferior turf varieties could result in contamination of our
own turf seed industry, so they introduced an “Acceptable
Cultivar List”. Only varieties that were tested and found
to have merit were allowed into the country. There was a fear that
the dwarf turf- type perennial ryegrass would spread their pollen
and cross contaminate our important pasture ryegrass seed industry.
After careful assessment it was realised that by using normal isolation
practices different varieties could be kept from cross pollinating,
so that now the production of turf ryegrass seed is an important
crop in New Zealand.
The first use of a turf ryegrass on sports turf was in the late
1970s when the cultivar Manhattan was imported from the USA and
sown in the Basin Reserve cricket pitch. Since then we have imported
turf ryegrass mainly from breeders in USA and some from Europe.
New Zealand breeders have been breeding successful varieties since
In recent years there has been a significant move away from the
use of fine grass species such as browntop (Agrostis capillaries)
and fine fescue (Festuca rubra subspecies rubra),
to the use of turf-type perennial ryegrass for lawns and turf. The
main reason for this change has been the dramatic improvement in
the quality of turf-type perennial ryegrass varieties. The rapid
germination and quick establishment of perennial ryegrass, even
in cold conditions, means that homeowners and contractors find the
new turf cultivars easy and reliable to establish. The lawn can
often be used four to six weeks after sowing, most months of the
The earliest turf ryegrass varieties were only marginally finer
than pasture types. Later, the varieties became finer, denser and
cleaner cutting. Modern turf ryegrass can be mowed at 12 mm and
from a distance look as fine as any lawn. The colour of perennial
ryegrass is usually darker than fine grasses.
Turf ryegrass did not gain immediate acceptance because it sometimes
suffered from poor persistence. In drier regions, ryegrass could
disappear completely over a single summer while in other areas it
appeared to perform well. In the 1980s, New Zealand scientists,
along with international collaborators, found that the surviving
grasses contained a fungus that grew within the plant. Because of
this, the fungus was called an endophyte (pronounced “end
- oh - fight”) with the generic name of Neotyphodium.
The association between the plant and fungus was synergistic, as
both organisms benefited. The endophyte gave the grasses resistance
against attack from insect pests, including argentine stem weevil
(Listronotus bonariensis) and black beetle (Heteronychus
arator), and contributed to their survival. The resistance
was due to the release of a number of different alkaloids, including
peramine. Infected plants did not have disease symptoms. The fungus
could only be passed on to non-infected turf through the seed of
infected grasses, and this helped explain why only some of the grasses
in the turf contained the endophyte and others did not. Its entire
life cycle takes place inside plant tissues. A plant does not become
infected from its neighbours, nor can it infect other plants. Since
it does not affect the appearance of the grass plant, its presence
can be detected only by laboratory analysis. Although seed may decrease
in endophyte over time, plants that are infected maintain their
endophyte fungus. It is best to plant endophyte seed within two
years of harvest because the fungus deteriorates gradually over
time, becoming attenuated and non-viable in three-year-old seed.
Within a year of the pasture discoveries, New Zealand turf grass
breeder, Alan Stewart, working at Pyne Gould Guiness Seeds in Canterbury
determined that almost all of the overseas-bred turf varieties lacked
endophyte. In collaboration with Dr Reed Funk, a plant breeder at
Rutgers University, USA, he soon determined that the endophyte also
gave resistance to sod webworm (Scoparia species) in turf
in the USA and to a wider range of other pests, making it valuable
in turf throughout the world. Endophyte presence in ryegrass is
now known to affect over 40 invertebrate pests, mostly those insects
feeding on the lower part of the tiller rather than root feeders
such as grass grub (Costelytra zealandica).
Turf breeders in the United States continue to produce a large
number of new turf ryegrasses with finer leaf texture and darker
colour each year, now all containing endophyte. Future research
is likely to lead to endophyte strains for turf, which will provide
resistance to an even wider range of insect pests than at present.
Endophyte-enhanced varieties also have increased growth and vigour,
making the varieties more tolerant of drought stress, summer weed
invasion, and other possible turf diseases. The advantages of endophyte
are most obvious during the late summer and fall months. Breeders
in New Zealand have concentrated on producing varieties adapted
to our climate. In particular they have led the way in introducing
active winter growth into turf ryegrasses so they perform better
on our winter sports fields.
Perennial ryegrass is versatile. It has excellent wear resistance
and is used on sports grounds and cricket pitches. Provided it is
sown heavily and kept frequently mown, it can be mown at 5 mm in
tennis courts, at 12 mm in golf course tees, at 15 mm on golf course
fairways, at 12-15 mm in a home lawn, at 20 mm in a cricket outfield,
and at 25 mm in a sports field.
Pasture ryegrass is nothing like turf ryegrass. It is coarse and
open textured, and produces lots of vertical leaf growth. The leaf
tips produce stringy white fibres making turf difficult to mow cleanly,
even with a sharp mower, and causes a frayed looking white colour
to the leaf tips. The stalky seed heads produced by the ryegrass
over a prolonged period over summer are also difficult to mow. Conversely,
turf types are fine, dense and compact growing, and mow cleanly.
Turf ryegrass produces seed heads over a short period and vegetative
growth resumes once it is cut.
Some of the new turf ryegrass varieties are so dark they are almost
black. The extremely dark colour presents the buyer with a dilemma.
While the very dark colour looks good when the lawn is newly sown.
Over time it will inevitably become invaded with browntop, Poa
annua and other grasses to form unsightly contrasting light-coloured
patches in the turf. Choosing a medium green-coloured grass means
that the lighter patches of the other grasses will be masked somewhat,
and the turf will still look good.
Much of the perennial ryegrass seed sold to homeowners is of indifferent
quality. Furthermore, seed that is stored for over 18-24 months
under normal seed storage conditions will lose its endophyte. Buyers
wanting to ensure they purchase seed of good quality should seek
the following information.
1. Is it a named turf variety that has been bred in the last 10
2. Is it a variety with high endophyte content?
3. Is the seed less than 18-24 months old?
4. Has it a high germination as evidenced by a recent germination
5. Does the purity and germination certificate state a high purity
The Australian grass micolaena (Microlaena stipoides)
produces hardly any vertical growth and requires less water and
mowing than conventional, warm-season exotic grasses.
Exotic, short-growing grasses that produce a small amount of clippings,
such as a type of couch grass code-named C118, grows horizontally
instead of vertically, and also requires less mowing than conventional
Turf grasses are suitable plants for monoculture because they
rejuvenate continuously. Turf species have a limited height, though
the leaf blade grows after cutting from an intercalary node just
above the soil (Figure 1). It produces new shoots from creeping
horizontal stems, thereby replacing old shoots, which die over time.
Turfgrass species have the ability to cover vast areas.
Turfgrass plants are made up of two components, the shoot system
and the root system (Figure 1). The shoot system is responsible
for manufacturing the food supply that is used by the plant, while
the root system is responsible for taking in water and nutrients,
and as such is more important in maintaining healthy turf.
Figure 1: The components of a grass plant.
A turf grass seed is made up of the seed coat, the embryo, and
the endosperm (Figure 2). The seed coat is the protective covering
on the seed, but is not hard and does not prevent germination. The
embryo inside the seed develops into the new turf grass plant. The
endosperm provides the food supply for the developing embryo. Once
the seed has started to germinate, enzymes are released to break
down the food reserves (endosperm) in the seed to provide the nutrients
As the embryo grows, the number of cells and their size increase.
The first part of the embryo to enlarge and break through the seed
coat is the primary root or radicle. The primary root develops into
a temporary (seminal) root system, which supplies the nutrients
and water for the early stages of seedling growth. Just after the
primary root emerges, the plumule, which is encased by the coleoptile,
breaks through the seed coat and begins developing into the first
shoot. The coleoptile is not a true leaf in that it does not have
the ability to carry out photosynthesis but rather is a protective
sheath for the plumule. Once exposed to light, the plumule photosynthesises
and continues to grow.
The growth and emergence of the coleoptile and plumule are dependent
on the food supply in the endosperm until photosynthesis begins.
Thus, placement of grass seed at the proper depth (2-4 mm deep)
is of utmost importance since the endosperm may be used up before
the new shoot can reach the soil surface and start making its own
Figure 2: Hypogeal (cotyledons remain below the soil surface) germination
patterns and structures of a typical grass seed.
The seminal root system is active for only a few weeks and is
composed of only a few roots. It decays two weeks after germination,
and the plant develops an adventitious root system, which arises
from stem tissue rather than from root tissue. The adventitious
roots, located at the base of the shoot, serve the plant's needs
for the rest of the plant's life. This system is characterised by
extensive branching and is very fibrous.
Fact: Soil supporting Kentucky bluegrass turf
can contain 1000 roots/cm³, including half a million roots
hairs, with a combined length of 1.2 km and a surface area of 420
Turf grass species have either an annual system, regenerating
their entire root system every year, e.g. perennial ryegrass, or
a perennial root system, retaining a portion of their roots in subsequent
years, e.g. Kentucky bluegrass.
A turf grass plant has a compound shoot system made up of a single
repeating unit called the phytomer, which comprises the leaf blade
and sheath and a bud at the base of the leaf sheath. The shoot does
not have elongated internodes so that the phytomers are stacked
on top of each other.
Peeling back the leaves of a turf grass plant will reveal that
the leaves that are pulled off consist of the blade and sheath.
The bud located at the base of the sheath will either not be visible
or will have developed into a tiller, rhizome or stolon.
The growth of the shoot system is similar to a collapsible telescope
that is made up of a series of concentric rings where the eyepiece
is the innermost and smallest ring. The youngest leaf of a turf
grass plant can be compared to the eyepiece of the telescope. The
oldest leaf of a turf grass plant corresponds to the outermost section
of the telescope. As a new leaf begins to grow, it emerges from
the leaf sheath of the next oldest leaf. The shoot system of a grass
plant originates from the crown at the base of the shoot. This is
where all leaves originate. The growth of the leaf is due to intercalary
meristems located at the base of the leaf blade and leaf sheath,
and away from the apical meristem. A meristem is an area of the
plant where new cells are produced by division of older cells.
Turf grass plants withstand mowing because their intercalary meristem
is located below the mowing height. Many broadleaf plants cannot
withstand mowing because their apical meristem is removed during
the mowing process. The leaf of a turf grass plant cannot grow indefinitely.
Once it has reached full expansion it will stop growing and remain
below the mowing height. The newest growth is always removed during
The bud at the base of the leaf sheath can either remain dormant
or develop into an intravaginal tiller, where it remains inside
the leaf sheath of the previous leaf, or an extravaginal tiller,
where the new tiller penetrates the leaf sheath and develops into
a stolon or rhizome. All turf grass species have intravaginal tillering,
e.g. perennial ryegrass, while some species have extravaginal tillering
in addition, e.g. Kentucky bluegrass.
Plants have the unique ability to photosynthesise; the process
of converting carbon dioxide and water to carbohydrates (sugars)
and oxygen with energy supplied by the sun. This process accounts
for 90% of the plant dry weight whereas only about 10% is derived
from minerals through the soil. Photosynthesis is summarised in
the following reaction:
CO2 + H2O
= CHO + O2
The carbohydrates (CHO) are then used by the plant to make energy
or stored for future use. Photosynthesis is highest in bright sunlight,
but cool season turf grass plants such as creeping bentgrass or
Kentucky bluegrass reach their maximum photosynthetic potential
at about one-third full sun.
The end product of photosynthesis is the simple six-carbon sugar
glucose. Cool season plants form two three carbon sugars, which
are combined to form glucose. This is called the Calvin cycle and
these plants are referred to as C3 plants. Warm season grasses like
zoysia and crabgrass have a different photosynthetic cycle and form
an intermediate four-carbon sugar prior to conversion to the six-carbon
glucose. These plants are referred to as C4 plants and have marked
differences in metabolism and response to environmental stresses
compared to C3 plants.
Photosynthesis decreases as temperatures increase beyond a maximum.
This is because the enzymes that attach to the CO2
molecule begin to lose their affinity for CO2
and begin to attach to O2, thereby decreasing
the photosynthetic rate. Oxygen is isolated from the photosynthetic
apparatus of C4 plants so these plants are more efficient at photosynthesis
than C3 plants, especially at warm temperatures. But C4 plants are
less efficient at photosynthesis in low light or cool temperatures
than are C3 plants. This explains why a C4 weed like crabgrass is
not a problem in the shade or during cool temperatures in spring
Carbohydrates are broken down in the process of respiration to
release energy, water and CO2:
CHO + O2 = H2O
+ CO2 + Energy
The energy is used to maintain life in processes such as protein
synthesis, transpiration and mineral uptake. Respiration occurs
constantly during the life of a plant. Like humans, respiration
in plants is highest at warm temperatures; the higher the temperature,
the higher the respiration. Respiration is very high in C3 plants
in hot weather. In prolonged hot weather, respiration may deplete
all of the carbohydrates in a C3 plant. C4 plants tend to have lower
respiration at high temperatures than C3. Thus C3 plants are not
vigorous during hot summer weather whereas C4 plants thrive in hot
Plants grow in two ways: cell division and cell elongation. Cell
growth takes an enormous amount of energy, which is derived directly
from photosynthesis or indirectly through stored carbohydrates.
Fact: For cool season plants, shoot growth is
at a maximum between 21 and 27°C. It is minimal between 0 and
10°C, and drops off sharply above 27°C. Maximum root growth
occurs when soil temperature is 16°C. Root growth occurs as
long as soil is not frozen but is minimal until soil temperatures
rise to 7°C. It ceases at temperatures above 21°C.
Growth is the first process inhibited by water stress. More growth
occurs at night because there is no water stress, unlike during
the day when plants are actively transpiring and creating a water
In turf grass plants, carbohydrates and other products are stored
primarily in the stem bases and crowns, but also in rhizomes and
stolons. These products are utilised for respiration during periods
of stress to help maintain the plant when photosynthesis is not
occurring or occurring at a low level. Storage products are also
used whenever the plant is forced to grow, such as after mowing
and nitrogen applications, recovery from a stress, or breaking winter
dormancy. The more carbohydrates that are stored in the plant, the
stronger it is.
These four processes can be combined into one equation to describe
Photosynthesis – Respiration = Growth + Storage
The left side of the statement symbolises net inputs whereas the
right side is net outputs. When photosynthesis is high, it provides
enough energy to support the other three functions. If photosynthesis
decreases for any reason, the storage products must provide for
respiration and growth if it is occurring.
The easiest way to maintain the maximum photosynthetic potential
of a plant, regardless of weather, is to maintain the turf at the
highest possible mowing height for the species.
Scalping a turf removes much photosynthetic potential and the
plant must "borrow" energy from storage to maintain respiration
and regrow. Repeated scalping will deplete storage, leading to poor
health and possibly death.
There is a direct relationship between cutting height and the
total storage volume of the root system, as the turfgrass plant
develops a balance between its top parts and its root system. When
the turfgrass plant is mowed, the plant no longer needs the same
size of root system, and the root system is reduced to achieve balance.
The lower the cutting height, the shallower the root system becomes
(Figure 3). A shallow root system impairs the plant’s ability
to withstand drought stress, and root pruning from grass grub (Costelytra
zealandica), striped chafer (Odontria striata) and
manuka beetle (Pyronota species).
Figure 3: Effects of mowing height on root depth of turfgrasses.
Furthermore, cutting height influences the ability of the plant
to protect itself from summer heat. The temperature-sensitive growing
points (crown) of the turfgrass plants are at or near the soil surface,
and are insulated to a certain extent by the surfaces of more mature
leaves. Reducing the cutting height subjects the plant to a greater
likelihood of high-temperature injury. As a consequence, the plant
may die, and the turf gradually thins out during summer.
Application of fertiliser stimulates turf grass photosynthesis,
respiration, and growth, but storage reserves are used. Respiration
increases because there is more plant material to keep alive. Fertiliser
application has different effects on plant metabolism at different
times of the year due to the varying physiology of the turf grass.
In spring, photosynthesis increases because it
is cool and sunny, respiration is minimal because of cool temperatures,
and growth is naturally increasing, which slightly depletes storage.
By fertilising under these conditions, growth is forced, increasing
respiration slightly and further depleting reserves and compromising
the plant later in the summer.
During the heat of summer, photosynthesis is
down, respiration is up, and as a consequence growth is reduced,
and storage decreases because it is being used to supply respiration.
An application of fertiliser forces growth, which increases respiration
and further depletes storage. Regardless of the amount of fertiliser
applied, photosynthesis is not increased because of high temperatures.
In autumn, cool season turfgrasses are under
the least stress and are thriving. Photosynthesis increases to a
high rate, respiration decreases to a minimal amount, and storage
is occurring despite the growth. Fertilisers applied at this time
will increase photosynthesis but since it is fairly cool, growth
will not be stimulated significantly and more carbohydrates will
be stored. With average temperatures of 10°C, fertilising increases
photosynthesis and since temperatures limit growth and respiration,
storage is increased dramatically.
Growth is stimulated by applications of nitrogen, especially at
rates above 300 g N/m². Thus nitrogen should be applied in
autumn to enhance turf density and rooting, rather than in spring
or summer when it stimulates unnecessary leaf growth.
By maintaining a proper balance between these four processes in
the plant, turf managers can maintain a healthy turf capable of
tolerating stresses. Proper cultural management is essential for
maintaining these processes in the plant.
The 16 nutrients required by turfgrasses for optimum growth are
listed in Table 1. Usually, only N, P and K are not available in
the soil in quantities sufficient for good growth, and must be periodically
added as a fertiliser. In acidic or alkaline soils, iron or magnesium
may be bound up in the soil particles, and may be required as a
Table 1: Primary sources of nutrients required by turfgrasses.
The turfgrass plant requires more N than any other nutrients.
Grasses usually contain 4-5% of their dry weight in N. Nitrogen
is a component of chlorophyll, and is crucial to the growth and
developmental processes in the plant. Since the addition of N increases
shoot or leaf growth at the expense of root growth, it is possible
to produce a turf with a large amount of green leaf growth but with
a restricted root system. Therefore, reasonable amounts of N are
generally desirable so that N that is surplus for top growth is
channelled into the roots.
However, high N levels produce a turf grass plant with thin cell
walls, making it susceptible to attack by fungi or insects, and
a high water content in plant tissue, increasing the requirement
for irrigation and making the plant more susceptible to heat and
drought stress. Furthermore, N-stimulation of leaf growth can deplete
nutrient reserves in the roots, reducing the ability of the plant
to survive dormant periods. Therefore, for these reasons alone,
application of N in summer is not recommended. A good fertility
programme should produce a reasonable amount of top growth, but
not at the expense of root growth.
Phosphorus facilitates energy transfer and storage within the
plant. The roots are a primary organ for energy storage and are
dependent on P levels in the plant. The demand for P is greatest
during formation and germination of seed. Since the turf plant is
not maintained for its seed production, its need for P is low. Therefore,
turf fertilisers for established lawns are low in P. Because germinating
seed has a high requirement for P, along with its property of being
fairly immobile in the soil, particularly clay soils where it may
take years for P to move a few centimetres, a fertiliser containing
a higher level of P, such as an N-P-K ratio of 1-2-2, is recommended.
Potassium regulates water relations in the plant. The absence
of adequate amounts of K and high N levels results in thin cell
walls and high water content. Increasing the ratio of K to N in
the plant induces thicker cell walls and higher cell moisture content,
allowing the plant to be less susceptible to fungal or insect attack,
and more tolerant of droughts. Furthermore, the rate of leaf growth
is reduced, thereby reducing the demand for nutrients by the leaves
and allowing the nutrients to be available for stolon, rhizome and
Potassium is easily leached in the soil, and may also be lost
from the plant through its leaves during rain or irrigation. Thus,
K should be applied to the soil at regular intervals at a constant
Thanks to Bill Walmsley, New Zealand Sports Turf Institute, for
his article which was abridged for the section ‘Perennial
Ryegrass for Lawns and Turf’, and Sam Wakelin for the drawings
in Figure 1, Figure 2 and 3. Thanks also to Robert Lamberts for
the photographs of weeds.