Perennial ryegrass is not well adapted to sandy or gravely soils.
It is best adapted to medium-textured, silt loam soils and clays.
While it can be maintained on sandy soils with irrigation and regular
fertilisation, it tends to be replaced by other grasses over time.
It performs best when irrigated over summer. It survives summer
drought best on heavy soils but is often killed on light sandy or
gravely soils.
Perennial ryegrass prefers a neutral soil (pH 5.5 - 6.5) and good
availability of phosphorus and potassium. Regular nitrogen fertilisation
is needed to maintain good colour and active growth. Perennial ryegrass
will grow more quickly and will need more mowing than fine grasses
such as browntop and fescue.
Regular cutting of the grass encourages tillering of the plant
to create a dense, healthy sward with an even, attractive finish.
Mowers
Two main types are available. A cylinder or reel mower type that
incorporates a roller provides the finest finish for a lawn and
creates stripes. A rotary mower type, which includes the hover mower,
is suitable for utility lawns. For both types, sharp blades ensure
that the plants can recover quickly with a reduced chance of contracting
diseases. On areas to be used for ball games, the direction each
time the lawn is mown should be varied to prevent a development
of a grain, which is caused by grass growing in one direction. It
affects the run and speed of the ball.
For the first cut of a new lawn, cut the grass when it reaches
5 cm, to a height of 2.5 cm, and gradually lower the cutting height
in subsequent mowings until the desired height is reached. Frequency
of mowing depends on the desired range in which the height of the
grass is to be kept, which is governed by type of grasses grown,
how the lawn is used, and the time of year.
For optimum appearance, cut the lawn as required to keep the grass
within a range of the lowest desired height, and the highest height
being two-thirds that height. That is, cut the plant no more than
to one-third of the initial height above the soil.
For high-quality lawns, cut the turf to 1.5 cm as needed throughout
the year. For utility lawns, cut the turf to a height of 4 cm as
needed in winter, and to 2-3 cm on a weekly basis during spring
and autumn.
Short lawns look neater but they suffer more stress, have shorter
roots and fewer new plants are made. This means that short lawns
require very careful management of watering, fertilising and mowing
to survive through the summer months.
In the heat of the summer when grass growth is low, the frequency
of mowing can be reduced while maintaining the desired lawn height
to enable the turfgrasses to withstand drought and summer heat.
And since many weeds need light to germinate, weeds are suppressed
when the soil is shaded by taller grass. Regular cutting allows
for short clippings, which fall down between the grass plants where
they mulch the soil, contribute to lowering soil temperatures and
enhancing moisture retention in the root zone of the soil.
Two or three different cutting heights in a lawn add texture and
interest to the garden. Areas used for playing or walking should
be cut to 1-2.5 cm, as this height protects the surface against
wear. Areas under trees can be mown every 2 weeks to a height of
5-10 cm to help retain soil moisture.
Rule: Mow when the grass has grown by 50%, so
you don’t have to cut off more than one-third of the blade.
If the lawn is less than 7 cm in height, grass clippings can be
left on the lawn after cutting, rather than removing them with a
catcher. The clippings decompose quickly, returning nutrients to
the soil within two weeks after mowing. The macro elements of the
clippings comprise nitrogen, phosphorus and potassium at a ratio
of 5:2:3. Trace minerals are also present. The amount of nitrogen
returned to the soil is as much as 88 kg/ha. Since nitrogen is the
most expensive component of all lawn fertilisers, it pays to leave
clippings.
Clippings also enhance the habitat for beneficial microorganisms.
Earthworms ingest the clippings at night, further increasing the
aeration and fertility of the soil, and maintaining a thatch base
that allows the lawn to feel springy when walked on. If the thatch
is removed, worms will migrate to other more favourable habitats.
If the worms migrate, or are killed, a deep thatch can result, causing
the soil to become compacted and less fertile.
However, for taller or ranker turf that mats after mowing, the
clippings are best removed.
Raking and removing or mowing fallen leaves during autumn-winter
is recommended otherwise a layer of leaves can reduce evaporation,
increase humidity and lead to lawn diseases.
Create a neat finish by trimming the lawn edges with long-handled
edging shears, circular edger, mechanical edging machine or nylon-line-trimmer
with an adjustable head for edge trimming. Trimming before mowing
with a rotary mower with catcher will allow the edge cuttings to
be removed with the clippings to enhance the finish. If the lawn
edges become irregular, recut them with a half-moon edger, cutting
against a plank for a straight line.
Regular applications of fertiliser ensure a vigorous healthy lawn.
Most of the nutrients essential for growth are plentiful within
the soil, except for nitrogen (N), phosphorus (P), potassium (K)
and iron (Fe). Nitrogen is removed in grass clippings, and is essential
for producing further growth that is stimulated by mowing. Nitrogen-deficient
grass is yellow-green, and lacks vigour.
Nitrogen produces deep green leaves, rapidly growing leaves and
shorter roots. Phosphorus facilitates metabolic functions plus energy
storage and use. Potassium is used to create cell components, and
it helps regulate respiration and transpiration. It helps the plant
grow, withstand environmental stress and resist disease.
Fertilisers should contain N, P and K. Select a fertiliser that
contains a mixture of slow and fast release N. This allows the lawn
to green up with 2-3 days and stay green for several weeks. Iron
can be used to control moss and some broad-leaved weeds. Iron darkens
the grass, making it appear greener without stimulating growth.
Some nitrogen fertilisers (e.g. ammonium nitrate) can lower soil
pH (i.e. increase acidity), which makes the soil unsuitable for
earthworms. This is liable to increase thatch but reduce earthworm
casts.
Two applications of fertiliser a year are sufficient. Apply in
late spring and early autumn. Nitrogen applied in summer may stimulate
lush growth and encourage diseases.
Apply fertiliser uniformly to avoid variations in growth and the
risk of killing the grass due to toxic doses.
For even application when applying the fertiliser by hand, apply
the recommended amount to small squares.
Using a continuous belt or drop spreader ensures even coverage
over large areas. Divide the fertiliser into two batches, and apply
half in one direction and the rest at right angles to it.
If using a spinning disc or broadcast spreader, set the machine
to half the application rate and make adjacent runs at half the
distance apart of the machine’s spread. Apply a known weight
of fertiliser to a known area at the recommended rate, to avoid
fertiliser toxicity.
To prevent corrosion to metal parts of the applicator, wash the
applicators with water after use.
Thatch is not just a collection of grass clippings caught between
blades of grass. Thatch is primarily grass root stolons and rhizomes.
In a healthy lawn, earthworms and soil micro-organisms break down
the thatch naturally. Thatch is a favourite food for earthworms.
It does not cause problems when it 1-1.5 cm thick and it acts as
a mulch, but if thatch becomes thicker than 1.5 cm, it suppresses
growth of grass, keeps water from penetrating the soil, and becomes
a perfect medium for fungus.
The thickness of the thatch can be ascertained by cutting with
a spade a 7 cm deep plug from a typical lawn area. Examine the sample
for a brown to yellow-tan layer, starting at the base of the grass
stems. There will be little soil in this layer, just a dense tangle
of roots.
Thatch can be a problem on a lawn that is intensely fertilised
and watered or on a lawn that receives infrequent cutting of on
acid soils with a low pH. Pesticide use is also implicated where
thatch build-up is a problem because some pesticides kill earthworms
that normally feed on bury dead grass. Frequent shallow watering
causes grass roots to grow at the top 1.5 cm of soil, creating ever-thicker
layers of thatch.
First, get rid of thatch and weeds on the parts of your lawn to
be over-sown. Use a hard steel rake and work it back and forth across
the sore spots on your lawn. Or rent a power rake or a power detacher.
You’ll have plenty of organic debris for the compost pile!
The rake or detacher will create shallow grooves in the soil,
which will catch the new grass seed that you spread. Scatter the
seed, rake it in, and water it as you would any new lawn.
The best time to seed is in late summer when weather is ideal,
relatively few weeds are sprouting, and it’s the best time
to mend your lawn.
Established turf generally withstands dry periods, but growth
is retarded in prolonged periods of moisture stress. To maintain
growth and colour in the lawn during dry spells, the lawn needs
to be watered. Under drought stress, turfgrasses dry up and the
leaves roll and turn a dull purplish colour, a process called dry
wilt. However, too much water may induce wet wilt, which occurs
when the soils become saturated, and the movement of oxygen into
the soil and carbon dioxide out of the soil ceases. Then, the plant’s
root system is unable to take in oxygen and give off carbon dioxide
and, as a consequence, the plant will soon die. Furthermore, excess
moisture can bring about disease pressure from fungi such as that
causing leaf spot.
Water any turf just before it begins to wilt. This stage can be
recognised because the grasses develop a dull purple cast, and the
leaf blades begin to roll or fold. Further, the grass does not spring
back after the lawn has been walked on.
Preferably, water early in the morning when conditions are calm
and temperatures are low, so less water is lost to evaporation.
Watering in late evening has the additional benefit of reducing
water loss to evaporation, but because the grass usually stays wet
all night, watering at this time can induce disease outbreaks.
On very hot days, when ground temperatures exceed 35°C, applying
3 mm at midday will alleviate heat stress. Small reductions in plant
moisture have large effects on turf because 90% of the total mass
of a healthy grass plant is water. Transpiration of water through
the stomata helps reduce the ambient temperature surrounding the
leaf. This reduces the stress experienced by the plant. The effect
is similar to perspiration in humans, where it reduces our internal
body temperature. Stomata in turf grass plants close when the internal
temperature reaches approximately 35°C or if the internal leaf
humidity drops below 100%. The internal leaf temperature often exceeds
the air temperature because the leaf is exposed to sunlight. A brief
watering at noon reduces the leaf and soil temperature while putting
the water in the root zone when the plant most needs it.
Water to a depth of 10-15 cm. Deep watering encourages development
of an extensive root system, enabling the plants to utilise nutrients
and water in the soil more efficiently than shallow root systems.
Light, frequent sprinklings produce shallow root systems, making
the lawn more susceptible to drought and soil-borne insect pests
that feed on roots, such as grass grub (Costelytra zealandica),
striped chafer (Odontria striata) and manuka beetle (Pyronota
species).
Fact: Turf requires about 109 cm of water per
growing season.
The soil type affects how much water is needed to wet soil to
the desired depth (Figure 4). About 1.3 mm water is required to
achieve the desired wetting depth if the soil has a high concentration
of sand, and about 2 mm of water if the soil is a loam. For soils
rich in clay, 25 mm of water is necessary to wet the soil to the
desired depth.
General guide: Turf needs about 21 mm of water
once a week during summer, with a supplementary irrigation at noon
during hot days.
The amount of water being applied can be determined by placing
a flat-sided container under the irrigator, and measuring the depth
of water in the container after a certain time has lapsed. Then
a timer on the sprinkler can be set so that the appropriate amount
of irrigation water is applied, after adjustments have been made
for natural rainfall.
The depth to which the water has penetrated can be determined
by either digging a spade spit and observing the depth to which
the dark-shaded water layer extends to, or by using an electric
moisture meter.
Rule: It takes at least 20 L water to wet 1 m²
of lawn to a depth of 21 mm.
Aeration of the soil allows deep root growth, enhances establishment,
and reduces soil compaction and excessive thatch. Methods of aeration
include scarifying, slitting, hollow tining (coring) and spiking.
Aerate during spring and autumn. Dry summer conditions make the
turf more susceptible to drought.
Scarifying
Scarifying removes thatch, permitting air to enter the lawn surface
and enhancing thatch degradation by micro-organisms. Rake the lawn
with a wire or spring-tined rake, or a powered scarifier, in two
directions, one at right angles to the other. Moss should be killed
prior to scarifying to prevent it spreading to other parts of the
lawn during scarification.
Slitting
A slitting machine comprises flat knife-like blades that cut slits
through the thatch to a depth of 8-10 cm, allowing air into the
soil.
Hollow tining
A mechanical or hand tiner removes cores of grass, thatch and
soil, making a series of holes across the lawn about 10 cm apart.
The cores need to be filled with a sandy top-dressing to prevent
them from closing.
Spiking
Achieved by using a mechanical or hand spiker or roller aerator,
or a garden fork. Angle the spikes back slight to raise the turf
gently, to encourage deep root growth by creating fissures in the
soil.
Immediately after autumn maintenance work, and on a dry day, apply
a soil-sand top-dressing to fill in core holes, level the surface,
and keep the lawn open and aerated, which helps breakdown the thatch
layer. A sandy mixture of a one to one mix of medium-fine sand and
sieved soil is suitable. Apply the mix at 1 kg/m² after scarification,
but if the lawn has been both scarified and hollow tined apply the
dressing at 3 kg/m². Using a spreader 1-2 m wide, brush the
mix into the surface and any core holes to level surface irregularities
and ensure that it does not smother the grass.
Rolling is not essential, but if conducted once in spring it helps
to resettle the lawn surface after the previous autumn maintenance
work and any frost heave. It also enhances recovery of turf that
has suffered attack by grass grub (Costelytra zealandica)
by increasing the contact between the pruned roots and the soil.
A roller or cylinder mower may be used. Avoid repeated rolling through
the year as this can cause compaction with associated problems,
particularly on heavy soils.
Poor drainage restricts oxygen and mineral intake by grass roots.
Pools of water remaining on the lawn after heavy rain or watering
signify that the soil drainage needs to be improved. This can be
achieved by installing drainpipes in the soil.
