With water restrictions the norm in South East Queensland, there are concerns that grassed areas will be replaced by dust.
Aside from the impact on aesthetics, cleanliness and the health of people with respiratory problems and allergies, a poor lawn can drop the overall value of your property by 5 to 10%. Unless you are completely prohibited under the by-laws of your local council from watering lawn and there is no natural rainfall, the following simple measures will enable you to sustain your lawn.
The development of a strong, healthy root system is encouraged when grass sod or seed has been established on a thick layer of friable topsoil. The deeper this layer, the greater the opportunity for turfgrass to establish deep, drought-tolerant root systems. In areas were the topsoil is shallow, this may require a combination of rotary hoeing and topdressing with a sandy loam prior to planting.
During times of drought, it is essential to aerate. If your lawn has not been aerated within the last 12 months, make this a priority. Many grassed surfaces have become compacted through trafficking and past deluges of rainfall, forming a surface hard pan. These surfaces prevent applied water from entering and becoming successfully stored within the soil.
Compaction layers can be broken up using a soil aerator. You can get a contractor to do this work, or hire equipment and do it yourself. The aeration equipment will spike the lawn, opening up a channel for water and oxygen.
As the surface of a soil dries out, it is not uncommon, particularly with sandy soils, to encounter the problem of water repellency. To test for this, fill an eye dropper and dispense a single droplet onto a dry exposed soil area. If this droplet does not soak into the ground within about five seconds you may have a problem. The longer it takes for the droplet to soak in, the more severe the problem. In some cases, droplets are still intact after 10 minutes.
Repellency is caused by the upper-most soil layer and the granules in it becoming coated with organic compounds from decomposing organic material. Sand is more prone to water repellency than clays. When water is applied, the soil dispenses it sideways, causing localised dry spots, a problem which is more pronounced in times of water scarcity. Soil rewetting agents can partially solve this problem. Products and professional advice regarding the range of soil rewetting agents on the market may be obtained from your local nursery.
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When considering how available water might be usefully applied to lawns, critically examine the micro-environments that exist in your yard. Shaded areas and areas receiving run-off from any incident rainfall near the roof-line or paths and driveways will not require as much water as high-sunlight exposed areas. Water use can be reduced in these areas.
During drought you cannot expect to have a lush, green, European-style lawn. The objective for lawns under drought conditions should be to maintain sufficient living top growth and root systems to hold soil in place. Under these conditions you need to accept that some varieties of grass will shut down and become straw-coloured or start to purple. When the rain does arrive, however, it is then a quick path to re-greening and improved vigour.
It can be tempting to re-design gardens to replace turf with gravel or paving. The consequence of this however is reduced flexibility in how this open space may be used, the additional build-up of reflected summer heat, and absence of all the attributes associated with having a living lawn.
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Turf species and varieties
Under Queensland conditions, both green and blue couch have demonstrated drought tolerance over a sustained period. There are a number of varieties of green couch (Cynodon dactylon) and blue couch (Digitaria didactyla) on the market. Of the green couches, the older varieties, Wintergreen and Greenlees Park, are still widely used, despite the introduction of a number of more specialised new releases. Blue couch is widely naturalised over much of Queensland and is sold as common Queensland blue, Aussiblue and Tropika.
Under dry conditions, the couches wilt and then tend to become straw-like. Their root systems are robust and generally survive to produce a rapid greening response as soon as water becomes available.
Sales of newer species like the buffalo grasses (Stenotaphrum secundatum), zoysia grass (such as Zoysia japonica) and seashore paspalum (Paspalum vaginatum) are increasing. Independent research is underway at the Queensland Primary Industries and Fisheries to study the drought tolerance of the buffalo grasses.
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Your times of access to water and when and how it is applied is subject to local council by-laws. Check with your local council for details. Within these constraints: less frequent but thorough watering will encourage greater root depth.
Infiltration is improved if the lawn is wetted, the water allowed to soak in for a short period and then the surface is watered again. This will allow the moisture to penetrate deeper into the soil, encouraging deeper roots, which are able to access more available soil moisture. Frequent light watering encourages shallow roots, and the plant will quickly require more water.
Water at night as the evaporation levels are far lower than during daylight hours. Use a sprinkler rose with a cut-off mechanism on the end of your hose when hand watering to obtain an even distribution of water that falls gently onto the grass. If bucket-watering, use a watering can.
As overall lawn growth is reduced during times of restricted watering, fertiliser use should also be temporarily minimised.
Each pass of the mower blade over a lawn produces a level of stress on the turf. Under moist conditions this is of little consequence as the grass is growing rapidly and is capable of a quick recovery. In droughted lawns new leaf blades do not readily regenerate. Reduce the frequency of mowing and increase the mowing height to retain more individual leaf blades as the lawn starts to thin out. Do not remove more than the top third of leaf growth at a single mowing.
It is also important to keep the mower cutting blade sharp. This will help to avoid feathering or tearing of the leaf blades and the subsequent die-back.
The best type of mower to use during a dry period is a mulching mower. This will return the clippings onto exposed soil surfaces and assist in the retention of any available moisture. Mulching will be most effective when some leaf blades are being recycled into the lawn, rather than just seed heads.
During times of stress, where possible try to minimise traffic on the grassed area. Trampled leaves and stems do not readily recover in times of restricted growth.
Avoid applying herbicides for weed control on droughted lawns. Although the herbicides may be registered for use on your lawn type, they may cause additional subtle stresses on your grass and exacerbate existing problems with lawn vigour during dry times.
Tips for managing turf in dry times
- prepare the soil surface to encourage the formation of deep grass roots
- treat water repellent soils
- water thoroughly and at night to reduce evaporation.
- split your watering times to reduce runoff.
- water according to the needs of different areas.
- accept a lower standard of lawn surface.
- use a mulching mower.
- reduce mowing frequency and increase the mowing height.
- minimise traffic.
- do not apply herbicides.