EIGHT PRINCIPLES OF WATERWISE GARDENS
1. Planning the garden
Sound planning will ensure you create an attractive and sustainable garden saving you both time and money.
Before starting a plan it’s important to think about your current and future needs. You may want:
- an outdoor entertaining area (protected from the hot summer sun) which is linked closely to the living areas of the house
- a small area of lawn near this entertaining space (or you may not need any lawn)
- play areas visible from the house (if you have small children)
- vegetable and herb gardens which should receive at least six hours of sunlight per day (it is convenient for regularly used herbs to be placed near the kitchen);
- a sunny area for clothes drying ideally located near the laundry (it may be possible to incorporate compost/worm facilities in this area as well as storage areas for tools and bikes)
- a chicken run
- screening shrubs to provide privacy from the neighbours and protection from strong winds
- feature trees which will provide summer shade to the house and garden and help reduce evapotranspiraton and provide strong visual interest in the garden
- to divide garden into zones – higher water use plants (usually closer to the house) and lower water use plants further away from the house. These separate sections can be watered at different times during the week – rather than watering the garden all at once
- to consider the amount of time you would like to spend maintaining the garden
- to determine how much you wish to spend on a landscape plan and on landscape construction. Many tasks like installing plants and mulching can be performed easily by homeowners helping reduce labour costs.
A Landscape Architect can help you plan your garden and can recommend a staged garden construction.
>> For a list of Canberra Landscape Architects
2. Improve soils
Most soils in Canberra are either clay or shallow soils over shale. Clay soils can become compacted and slow to absorb water.
Soils can be improved by the addition of organic matter such as horse, sheep and chicken manure, preferably sourced locally, green manures, home made compost and gypsum. Organic material will need to be added on a regular basis, for example once a year. As well as improving nutrients and the structure of the soil organic matter is able to retain significant volumes of water - which is an added bonus for plants.
Remember locally occurring plant material is adapted to impoverished soils and should cope well in unimproved garden soils. Local species grown in improved soils will appear lusher than those occurring in local bushland due to the extra nutrients and water they receive.
3. Group plants with similar water needs together
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To water efficiently it is important to group plants with similar water needs together. Ensure you have a greater proportion of low water use plants in your garden than thirsty ones.
Many locally occurring native plants and exotic plants from dry regions (like the Mediterannean, parts of Africa and the Middle East) can be combined successfully in Canberra gardens. It is best to choose plants that occur in regions with low rainfalls, similar soil types and climatic extremes.
However, thirstier plants may have a role in our gardens. You may choose to create an oasis-like zone of higher water use plants close to the house. If well sited, a courtyard on the eastern or southern side of the home, may aid in keeping the building cooler over Summer reducing the need for energy guzzling air conditioners.
Plants which require significant amounts of water include hanging baskets, pot plants, annuals, lawns, vegetable, fruit trees and shallow-rooted shrubs from high rainfall areas.
Low water use, silver foliaged plants are grouped together including the highly textural Stachys lanata (Lamb's Ears) in the foreground, Nepeta (Catmint) and Westringia longifolia. Photo Edwina Richardson. |
4. Mulch
Mulch performs a number of beneficial roles in the garden – it helps protect the soil from drying out, suppresses weeds, adds organic matter to the soil and can reduce erosion. A layer of 75-100mm depth of coarse mulch is recommended over garden beds. Ensure mulch is not banked up around plant stems as this can cause collar rot leading to plant death. There are two main types of mulch – organic and inorganic.
Organic mulches include materials that break down. Readily available types from landscape suppliers include: pine flake, eucalyptus chip, 'Forest Litter', lucerne and pea straw. ‘Forest Litter’ is a recycled product produced from green waste at Canberra’s green waste recycling depots.
Studies indicate that coarse mulches are preferable to fine mulches. In fine mulches the smaller particles have a tendency to compact into an impenetrable layer, preventing water from reaching the soil. Depending upon the type of mulch chosen it will require regular replacement – for example an organic mulch like ‘Forest Litter’ may require topping up annually.
Groundcovers, which are low growing plants usually less than 500mm high, can act as ‘living mulches’ protecting the soil from the drying effects of wind and solar radiation. They can also act as soil binders, preventing erosion.
Inorganic mulches include products which don’t decompose such as gravels, ornamental pebbles and crushed brick and concrete. They suppress weeds and protect soil but don’t add organic material to the soil. Crushed brick and concrete products may alter the soil PH and should only be used around plants that can tolerate alkaline conditions. Remember to try to use inorganic mulches like crushed brick or concrete from local sustainable sources.
>> Choosing sustainable landscape materials.
5. Install drip irrigation
Drip irrigation ensures water is delivered to a plant’s root zone where it is most needed. There is significantly less evaporation of water applied with drippers than by conventional sprinklers. Run-off is reduced as the water is applied slowly. Use drip irrigation according to local water restrictions – aim to water deeply and less frequently.
Follow the three steps when using drip irrigation:
- Irrigate (recommended application rates for established shrubs are between 2 and 4 litres per week). Ideally water garden for 5 or 10 minutes. Leave for two hours to allow water to penetrate the soil.
- Investigate – using a hand tool like a trowel, dig down below the mulch to see how far the water has penetrated. If the water has been running off the surface your soil may be hydrophobic and require remediation eg with a soil wetter.
- Act - only turn the drippers back on for a short period (of 5 to 10 minutes) if the soil is dry.
For established plants, aim to water once per week, and if soaking rains occur, reduce watering accordingly. Anectdotal evidence suggests more plants die from over watering rather than under watering.
6. Reducing or removing lawns
During the 1980s almost 80% of water used outside the home was poured onto ACT lawns. In countries like England lawns can grow without a constant summer water supply - this is not the case in Canberra.
In the past lawns were almost always included in a garden design and covered significant portions of the garden. Although lawns are inexpensive to install and provide an instant effect, most lawns of exotic species require high amounts of water use in summer and regular maintenance like mowing, coring and fertilising.
When planning a new garden or remodelling an existing one, consider what the lawn is used for (Canberra is provided with many irrigated public spaces where large scale activities can occur such as soccer, cricket and kite flying.) Ask yourself the following questions: is a lawn desired for its visual appeal, does it provide a role in reducing solar radiation to the building or is it required for children’s play? When you have thought about your lawn requirements, consider how you might reduce your existing lawn. Think about substituting parts of the lawn with groundcovers, mulch or gravels if you are still wanting to achieve the appearance of an open space. Alternatively consider widening your shrub borders with some ground covers and strappy plants, thus reducing the total lawn area.
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Native grasses such as Microlaena stipoides (Weeping Grass) & Danthonia species (Wallaby Grass) can be used to create a low use lawn area. Lawns of Microlaena have been successfully established in Canberra and require minimal watering once established & occasional mowing.
Left: A lawn of Microlaena stipoides in Landscape Architect, Jennie Curtis' garden in Florey, ACT. Photo Jennie Curtis.
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ACTEWAGL are currently undertaking a trial of exotic turf grasses at Rosary Primary School in Watson to find the best grass mixes suitable for different applications.
>> For more information on exotic turf trials.
A number of gardens exist in Canberra where there the lawn has been removed altogether - reducing the need for ongoing maintenance and use of resources.
>> See Richardson Garden, Hackett Case Study
7. Regular maintenance
Regular maintenance such as soil improvement, pruning of plants, topping up mulch and adjusting irrigation systems can help reduce the amount of water used in the garden.
Irrigation systems should be regularly checked for leakages and it's important to dig down into the soil to see if the effective root zone is being wetted by the watering system. Anectdotal evidence suggests more plants die in Canberra from over-watering than under-watering.
8. Water harvesting
Water harvesting refers to collecting water on site that would normally be piped away via the stormwater system. There are a number of advantages of on-site water collection:
- water is stored in soils and made available for plants
- recharge of water aquifers
- reduction in the quantity of stormwater entering our drainage systems
- filter nutrients entering creek systems
- habitat provision
- recreates original drainage form such as ephemeral creek lines and the ‘chain of ponds’ which existed prior to European settlement.
Water can be harvested on the site in other ways, for example, through:
- Permeable paving includes unit paving (such as clay pavers), porous pavers and gravel. They allow water to infiltrate through sub-surface layers rather than being directed immediately away into the stormwater system.
- Swales are depressions or ditches with a longitudinal crossfall. They act to direct water away from a building either to garden beds or to a pond or wet area of the garden. Traditionally they were grassed however they can be lined with rocks and pebbles and wetland plants, such as Juncus.
- Bioswales are swales with a sub-surface layer of gravel or sand beneath them and buried pervious pipe. Low intensity flows filter through these permeable layers treating water both physically and biologically. Bioswales are best planted with native plant species which can cope with cycles of drying and wetting.
- ‘Dry creek bed’ is often a combination of a swale and small ponds designed to look like a natural creekline. It may become a main feature in the garden and directs water away from the building.
- Reed Beds have been used in commercial applications to slow down water from large impervious areas such as carparks. They are planted with wetland plants which trap nutrients & sediments helping cleanse water before it reaches downstream waterways. There is potential to apply these systems to residential settings.
- Temporary ponds (detention basins) – slow down the water movement on the site
- Ponds (Retention basins) – water is directed usually to the lowest point of the garden via a series of swales, dry creek beds or pipes. These are usually permanent water bodies which require topping up with rainwater during hot weather. Generally these ponds will require a pond liner to make them waterproof.
- Bogs are wet areas of ground with a high organic content where water loving plants such as Carex gaudichaudiana are grown.
- Interceptor channels are channels, approximately 300mm deep (a spade depth) and 100 to 300mm wide filled with rubble or gravel. They are generally placed parallel to contours. Water running down a slope is intercepted in the channels and made available to plant roots. These measures are particularly useful in clay soils which often become hard and impermeable to water during hot weather.
>> Fore more information on Water Sensitive Urban Design - Refer to ACTPLA Draft Guidelines
Stormwater is harvested in this garden pond in the Lawrence Garden, Higgins. The pond is topped up during the Summer months with rainwater collected in tanks. The pond is visually delightful and attracts a range of invertebrates and frogs. Photo Edwina Richardson. |
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As well as creating swales or ponds, water can easily be directed off paved areas onto garden beds rather than into the stormwater system. Remember to only pave where you ‘sit, stand and walk’. Incorporating porous materials into the garden like crushed brick, gravels and mulches means water can slowly soak in to the ground rather than rapidly running off surfaces. |
Generally, these passive forms of water collection cost no more than traditional engineered systems of drains and pipes.
Examples of water harvesting in public spaces in the ACT
- Ainslie Village, Ainslie, Canberra: designed by Landscape Architect Glen Wilson, was one of the first places in Canberra to incorporate a suite of water harvesting techniques.
- Innovation Centre, University of Canberra: designed by Landscape Architect, Jamie Dawson, of Envirolinks.
- David St Wetlands, O'Connor: designed by Landscape Architect, Jamie Dawson, of Envirolinks.
Visit demonstrations of gardens employing water harvesting
- Xeriscape Garden, Canberra Institute of Technology, Heysen St, Weston, ACT
- Lawrence Garden, Cussen St, Higgins, ACT. This garden illustrates how a number of changes that the owners implemented themselves relatively cheaply reducing their external potable water use by around 90%. The garden will be open through the Australian Open Garden Scheme in April 2008.
Example of Xeriscape garden employing water harvesting principles
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The 'Oasis Zone' at 9 Roma Mitchell Street, North Watson. The gravel area planted with Restio tetraphyllus is designed to intercept stormwater from the patio and allow it slowly infiltrate into the ground. This home and gardens was featured in the 'Ecoliving' display during 2006. |
>> Click here for Landscape Plan of Xeriscape Garden at North Watson by Landscape Architects JEA.
Traditionally water has been collected in the landscape with rainwater tanks. Tanks can provide a number of benefits - they collect summer rainfall that might otherwise not be generated from a dry catchment. They also slow down the first flush of stormwater which degrades local catchments. For people concerned about drinking recycled wastewater, which may soon be introduced to Canberra, they provide an alternate source of drinking water.
Rainwater tanks are most effective in Canberra when plumbed internally to provide the water for toilets, laundry and hand basins - rebates are available from the ACT government. One downside of rainwater tanks based on a whole of life analysis, is that they are a costly way to supply water compared to mains supply.
>> For information on grey water
>> For more information on installing water tanks in the ACT
References
ACT Government (2006) Think water, act water: strategy for sustainable water resource management in the ACT (2004-2005) Progress Report Office of Sustainability: ACT.
Cullen, Peter 'Water futures for Canberra: moving towards sustainability?' in Furnass, Bryan; Clark, Sebastian and Ramsay, Penny (2005) Making Canberra sustainable. Papers presented at Manning Cark House, October 2005. Ginninderra Press: Canberra.
Thompson, Paul (1991) Water in your garden. Lothian: Victoria.
Van Dok, Wendy (2002) (revised ed.) The water efficient garden. Water-efficient gardenscapes: Victoria.
Windust, Allan (2003) Waterwise house and garden. Landlinks Press: Victoria.
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