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Turf
 
                   
 
 
 
 
Maintaining a desired height
Mowers
Cutting height and frequency
Lawn clippings and mulching
Removing fallen leaves during autumn-winter
Trimming edges
Fertiliser
Types
Application
Thatch
Controlling thatch
Over-seeding a lawn
Watering
When?
How much?
Turf aeration
Scarifying
Slitting
Hollow tining

Spiking

Top-dressing
Rolling

Alleviating soil compaction

 

Routine care of grass lawns and turf

Management of turf ryegrass

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.

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Maintaining a desired height

Mowing

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.

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Cutting height and frequency

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.

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Lawn clippings and mulching

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.

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Removing fallen leaves during autumn-winter

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.

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Trimming edges

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.

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Fertiliser

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.

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Types

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.

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Application

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.

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Thatch

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.

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Controlling thatch

Using a power detacher can reduce the amount of thatch in a lawn. Detach in early autumn in preference, or alternatively in spring.

For long-term control, the causes of the thatch build-up need to be addressed by changing the existing maintenance practices.

Reduce the amount of chemical fertilisers being applied and reduce soil acidity (increased pH).

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Over-seeding a lawn

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.

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Watering

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.

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When?

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.

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How much?

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.

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Turf aeration

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.

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Top-dressing

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.

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Rolling

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.

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Alleviating soil compaction

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.

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