Saving Water in the Garden
General design principles
Hydrozoning
Soil improvement in the garden
Soils for containers (including hanging baskets)
Mulching
Changing an established garden
Maintenance
Bedding plants
Fruit and vegetables
Approximately half of all household water use is outside the home. Climate change and growing demand for water mean that water efficiency is more important than ever. Rainfall in WA has been decreasing since the mid 1970s and our aquifers are falling as less water filters naturally into them. Inflows into our dams continue to decline and although we have another desalination plant on the way, it is essential that each household with a garden plays their part to reduce their water use. There are several ways you can plan and maintain your garden so that it will need less water, but still be a thriving, attractive and colourful place to be.
|
Planning
Edited by John Colwill
Before planting you will need to investigate and analyse
- Orientation, sun and shade, the prevailing winds.
- Topography, water run off.
- Soil types, water holding capacity compaction, water repellence, fertility levels.
- Availability of accessible ground water.
- Views both inwards and outwards.
- Overall area available for the garden.
And consider your other needs for
- Utility spaces (clothes drying, compost and storage areas).
- Outdoor living spaces (barbecues, seating areas).
- Special needs (vegetable garden, swimming pool; etc.).
- Functional and aesthetic requirements.
- Plant preference and design styles (native / exotic, formal / informal etc.).
- Maintenance expectations.
- Budget available.
General design principles
- Do not plant areas unless it is necessary for functional or aesthetic reasons.
- Maximise the use of non-planting treatments such as paving and mulches.
- At the same time, beware of excessive unshaded paving which can be hot and glaring.
- Vary materials and arrange planting to frame and shade paved areas.
- Make use of windbreaks, pergolas, screen, lattice, shadecloth and vines to shelter the house, outdoor living areas and plants.
- Keep planted areas dense and consolidated. Sparse scattered plants are more difficult to water efficiently than ones that are in defined areas.
- Keep lawn to the minimum consistent with functional and aesthetic requirements.
- Avoid planting lawn on slopes or in narrow necks or paths which are difficult to water efficiently and maintain.
- Garden design blueprints in a variety of themes are available from leading nurseries.
Hydrozoning
|
Apply the principles of hydrozoning to plant selection and arrangement:
- A broad selection of plants may be used, but keep high water-demand plants to a minimum.
- Arrange plants having similar water requirements together (hydrozoning) and take this into account when deciding soil improvement and mulching, and when managing irrigation.
Some leading nurseries label their plants with drop icons signifying the appropriate hydrozone, described in three categories:
- Primary (3 drops) high water use plants.
- Secondary (2 drops); moderate water use plants.
- Elemental (1 drop); low water use plants.
Soil improvement in the garden
Adding organic matter to the soil improves both its moisture and nutrient holding capacity thus saving on water and fertiliser. It is particularly important to improve the top 15-20 cm of soil where the feeder roots of plants will develop. Old animal manures, compost and proprietary products are ideal soil improvers. Mix them in equal parts with the soil prior to planting out.
Use these points as a guide
- Shrubs, groundcovers and climbers 30 cm in depth and up to half a metre across.
- Trees 40 cm deep and 1 metre across and bedding plants 25 cm deep for the whole bed.
- Garden soils are just as prone to becoming non-wettable as are lawn areas.
- A regular application of a soil wetting agent in spring is recommended.
Soils for containers (including hanging baskets)
- Choose the best quality potting mix you can afford, preferably one approved by the Australian Standards Association.
- The water and nutrient holding capacity of potting mixes can be further enhanced by the use of water absorbent polymers. Some potting mixes already contain them.
- Most plants are now grown in soil-less mixes which become non-wettable if allowed to dry out. Soil wetting agents are also very useful, and may need to be applied more than once a year.
- A regular application of a soil wetting agent in spring is recommended.
Mulching
|
Mulching is enormously beneficial for all plants. The mulch should be spread over the entire planted area to a minimum thickness of 50 mm.
Organic mulches are preferred because they
- Break down over time and feed the plants.
- Improve the soil organic matter content as they break down.
- Reduce evaporation loss from the surface.
- Encourage earthworms and soil microbial activity.
- Restrict weed growth. Any weeds which do germinate are easy to remove.
- Prevent wind and water erosion.
- Protect the roots from daily temperature fluctuations.
- Improve the appearance of the garden area.
Mulching material
- Raw materials like woodchips, chipped tree waste or similar, whether bought-in or homemade, are ideal mulching materials. However, if the mulch is watered regularly you may need to add some extra nitrogen in the form of animal manures, blood and bone, etc, to prevent the natural breaking down process from drawing nitrogen away from the plants.
- Materials such as lucerne hay, pea straw, seaweed and compost can be used for mulch, but since they are more expensive and break down quicker, they are best used within the drip zone of plants.
- Lawn clippings do not make a good mulch, they are best composted. However, if mixed with a coarser material like chipped prunings or woodchips they can be used as a mulch.
- Old newspapers can be used under a mulch as a weed control layer, however, thick overlapping layers of newspapers may prevent water penetration.
Applying mulches
- For general garden use mulches should be spread at 50-75 mm thick.
- Always leave a breathing space of 50 mm around stems and trunks of plants.
- Organic mulches enriched with animal manures are enormously beneficial when applied thickly (to 30 cm) around the drip zone of fruit trees. They should be topped up as necessary during spring, summer and autumn to maintain a minimum thickness (after settling) of 15 cm.
- Vegetable gardens should be mulched with ´softer´ mulches such as compost, pea, hay or lucerne straw or seaweed.
- In garden areas mulches should be topped up as necessary; perhaps twice a year in both autumn and spring.
- Mulches should never be raked up, turned over, dug in or disturbed in any way. To do so will damage the fine feeder roots which plants develop in the zone between the mulch and the soil.
Changing an established garden
If your garden has grown like topsy with little bits all over the place you can change it round.
- Most of the high water use plants have shallow root systems and can be easily transplanted in winter into their respective groups.
- Hardy, low water and drought tolerant species cannot normally be moved because of their very deep root systems.
- The type, area and location of lawn in the garden can be reconsidered. If you choose to convert some areas of lawn to a lower water use treatment make sure that the replacement plants or ground treatments are more water efficient than grass. Check with your local member of the Nursery Industry Association.
Maintenance
- Do not force plants on with large amounts of strong fertilisers. These produce lush growth that has a high water transpiration rate and is more prone to insect and fungal attack.
- Slow release fertilisers, including animal manures, are the best type. They produce steady, healthy growth and minimal leaching of nutrients into the ground water.
Bedding plants
- Plan your flower beds to be mass displays.
- Do not place a few plants here or there in odd spaces all over the garden, but rather group your flowers together in a suitable area which can be watered independently of other areas of the garden.
Fruit and vegetables
These are generally high water use plants which need a sunny position. Site very tough shrubs on the exposed side to act as a windbreak and protect them. Slowing down the hot dry winds is a very important water saving feature. It will also prevent damage to the more delicate plants.
Prepared with the support of
Nursery Industry Association
Irrigation Australia
Australian Institue of Landscape Architects
Turf Growers Association
Landscape Industry Association
Independent Lawn Mowing Contractors.