Every drop counts
Green open space is important!
The Royal Botanic Gardens advocate green open space for a number of considerable benefits.
- Community wellbeing - our mental and physical health is supported through passive and active recreation in green open space
- Environmental cooling - plants can reduce the air temperature by 2-8 oC. Turf areas can be 15 oC cooler that adjacent asphalt. This cooling ability of plants will increase in importance during a warming climate.
- Carbon storage – soils with healthy plant cover tend to store more organic matter (carbon).
- Scientific value - there are over 10,000 species of plants in the Royal Botanic Gardens. Many of these plants are irreplaceable, endangered or even extinct in the wild. It is important for conservation that the survival of these plants is supported by an adequate supply of water.
However, the Royal Botanic Gardens also promotes efficient irrigation (where needed) of green open space so that energy and water is not wasted.
The importance of conserving green open space! In the foreground is Guilfoyle’s Volcano (circular area) under construction within the Royal Botanic Gardens Melbourne. The buildings of Melbourne city can be seen in the background. (Photo used with permission - Karl von Moller Feb 2009)
People enjoying solace in green open space at the Ian Potter Foundation Children’s Garden RBG Melbourne.
How does the Royal Botanic Gardens conserve water?
Horticultural staff have extensive training in current irrigation management principles and efficient operation of the irrigation system.
Turf areas are being converted to warm-season grasses such as Kikuyu, which are more water efficient than cool-season turf like Ryegrass. Warm-season grasses typically use up to 30% less water than cool-season species.
A weather-based irrigation scheduling system is used that accounts for plant requirements, climatic conditions, soil water-holding capacity and rooting depths to maintain plant health, rather than promote excessive growth. This means that plants are not watered too frequently – increasing the opportunities to make best use of any rainfall. Efficient irrigation scheduling means that the right amount of water is applied at the right time.
Mulch is used on garden beds. About 1500 cubic metres of recycled plant material is composted to apply 300 cubic metres of mulch to garden beds every year. The mulch depth is typically between 50-75mm. The mulch minimises soil water losses from evaporation and improves water-holding capacity of the soil.
The RBG Melbourne uses water-sensitive design principles for all new landscape areas. The Water Conservation Garden, indigenous plant landscape at Long Island, and the more recent Guilfoyle’s Volcano development are key examples of this approach. The following collections feature plants adapted to dry conditions:
- Arid Garden (cacti and succulents)
- California Garden
- Cycad Collection
- Grey Garden
- Lower Yarra River Habitat (indigenous plants of Melbourne)
- Southern Africa Collection
- Water Conservation Garden
- Guilfoyle's Volcano
Through the use of an Automatic Weather Station, rainfall, solar radiation, air temperature, wind speed and relative humidity are continuously monitored and these readings are used to estimate the evapotranspiration rate of each plant category in the Gardens.
The performance of the irrigation system equipment, sprinklers and sprays is routinely checked through irrigation audits, and the system is regularly maintained. A well-managed irrigation system ensures a high level of water use efficiency, which saves water.
Irrigation water use is regularly monitored, compared with past years and climatic conditions, and reported monthly across the Royal Botanic Gardens to assist the development of 'water-saving consciousness' in the culture of the organisation.
Irrigation Index and Aggregate
An Irrigation Index is a management performance indicator to compare estimated water needs with what was actually used in the landscape.
A value of 1 or less is an "ideal rating". If a value of 1.08 was obtained, this can suggest overwatering by 8%.
Since 2001, the average annual Irrigation Index has been 1 or less compared to Ii 3.2 in 1994-95.
Irrigation is used to support the health of the living landscape when rainfall is insufficient. The Garden's target aggregate of irrigation and rainfall is a total of 900mm per annum.
Due to improvements in efficiency, the annual average irrigation amount has been reduced to about 458mm compared to 965mm of irrigation applied in 1994-95.
The Irrigation Index is a management performance indicator to compare estimated water needs with what was actually used. A value of 1 or less is an "ideal rating". Values higher than 1 suggest overwatering has occurred.
How can you conserve water in your own garden?
Decide what areas or plants actually need additional watering
Many plants will survive on the water supplied by natural rainfall. For example, locally-native species are adapted to the weather conditions in your area. Many plant species from arid and Mediterranean climates can also survive for long periods without rain or supplementary irrigation.
Irrigate your plants according to weather conditions
How often you water your plants will need to be adjusted from week to week. Depending on rainfall, no irrigation may be needed for established plantings in winter compared to once every 7-14 days in summer. Regularly adjust timers and controllers to ensure the right amount of water is applied at the right time.
Group together plants with similar water requirements.
Some plants need more water than others. By grouping plants with similar water requirements, you can help to prevent over-watering or under-watering individual plants. It can also simplify the design and operation of an irrigation system.
Choose plants with adaptations that make them natural water savers.
In general, plants with hairy, succulent, wax-coated leaves or with fine, stiff foliage are more likely to be adapted to growing in dry environments. Grey- or silver-foliaged plants are also usually suited to dry conditions.
Apply a layer of mulch annually to help minimise water-loss from the soil.
Mulch improves the long-term water-holding capacity of the soil (through the gradual increase of organic content) and also restricts weed growth that may compete with plants for water. It should be applied in layers no deeper than 50-75mm maximum thickness. Mulch that is too thick or too fine will actually prevent rainfall and irrigation from reaching the soil.
Consider replacing part or all of a lawn with a woody groundcover or change to selected *warm-season grasses or locally native grassland.
Cool-season grasses such as Ryegrass usually need regular watering. *Warm-season grasses such as Buffalo, Couch or Kikuyu use water more efficiently (up to 30% less) and more readily tolerate drought. Locally-native grasses are adapted to seasonally dry weather.
*Some warm-season grasses can be environmental weeds and invade natural habitats. Please check if this will be a problem for your local area with horticultural experts or local government prior to planting any of these species in your situation.
Water deeply between the evening and early morning.
This is when evaporation from soil and transpiration from plants is at its lowest. Watering deeply provides a larger 'reservoir' of water in the soil and also encourages the development of deep root systems that help your plants cope more readily with dry conditions.
A day or so after watering dig some small holes around your garden to check how far the water has penetrated into the soil (wetting front), and note how deep the fibrous roots of your plants penetrate down into the soil – this is known as the effective root zone. Often in urban landscapes this zone won’t be much deeper than 30cm. Appropriate adjustments can then be made to the watering time to ensure that the full depth of the effective root zone is moistened. About 10mm (sandy soils) to 30-40mm (loamy soils) of water may be needed to wet the soil to a suitable root-zone depth.
Get to know your garden and its water needs.
Conditions within a garden can vary dramatically. There might be cool, shady areas or hot, dry areas; sections with well-drained soils or boggy soils; sloped or flat areas. Take advantage of this by choosing plants that are suited to the 'local' conditions or microclimates of your garden.
Understand the performance of your irrigation system or sprinklers
There is more to watering your plants than just turning on a tap or setting a timer. A well-designed irrigation system will apply water uniformly and at the correct precipitation rate. High watering rates can result in runoff rather than infiltrating the soil. Check the uniformity and application rate by using a number of catch-cans (pet food tins are suitable) spaced evenly between sprinkler heads. Measure depth of water in tins (in mm) after watering .For many soils, the precipitation rate should be less than 10mm per hour. If this is being exceeded, cycle your irrigation by operating for short periods with time for soaking allowed in between. Significant variation of water depths between the catch-cans can suggest poor efficiency. Consider changing sprinkler types and/or spacing. The watering diameter of sprinklers should reach each other, or what is termed 'head to head' spacing. Seek irrigation system advice from a Certified or Qualified Irrigation Designer.
Good maintenance keeps a dry garden in great condition.
Regularly check for pests and diseases, and keep your garden weed free. Ensure that your sprinkler system is operating efficiently to avoid wasting water.
Improve your soil.
In new garden beds, incorporate no more than a 4cm deep layer of quality, well-composted, fine organic matter in the top 20cm of the soil profile. This should improve the water-holding capacity of the soil. For established gardens, the regular application of mulch will also improve water-holding capacity by gradually increasing the organic content of the soil.
RBG Cranbourne and the Australian Garden
The Australian Garden at RBG Cranbourne, showcases the amazing plants of Australia. Visitors can discover the unique ecology of Australian plants, their adaptation to dry conditions and how to use Australian plants in their home gardens.
Water sensitive landscape design ensures that the Australian Garden is a low water-use garden, demonstrating the beauty of Australian plants.
Since 1994 the Royal Botanic Gardens has led the way in water conservation for large landscapes.
RBG Melbourne is recognised as one of the world’s finest botanic gardens. There are over 10,000 species and 50,000 individual plants in the 38 hectare gardens, including trees and plants of great cultural value. Many of these plants are irreplaceable, endangered or even extinct in the wild. It is important that the survival of these plants is guaranteed by an adequate supply of water.
Through expert management and efficient irrigation, RBG Melbourne has reduced its water consumption, while maintaining the beautiful, heritage gardens, during 13 years of prolonged drought.
The Royal Botanic Gardens is working with South East Water Limited to minimise water usage during water restrictions.
Water conservation achievements
Reduction in water use
For the last few years RBG Melbourne has used only 40-50% of the amount of water for irrigation that was used a decade ago. This has occurred during 13 years of sustained ‘driest on record' drought conditions since 1996. There has also been about a 30% visitor increase to the Gardens since 2006 which can increase landscape stress and watering requirements. We have achieved water savings through staff training and awareness of water issues, irrigation system development, and improved horticultural practices.
With the continuing partnership and support of South East Water Limited, an audit of domestic water use was commissioned for all RBG-managed facilities in December 2005. This has continued to contribute to a reduction of around 20% in domestic water consumption for 2006-07 compared with 2005-06. Overall, there has been a 36% reduction in domestic water consumption since 2001.
- In 2003, RBG Melbourne won the Sustainable Garden, Garden Design Category of the savewater! awards® for the Water Conservation Garden. RBG Melbourne was also recognised for efficient water use as one of two finalists in the Efficiency in Government, Government agency category of the savewater! awards®.
- In 2004, RBG Melbourne was again recognised for efficient water use by winning the Garden Design/Construction Category of the savewater! awards® for the Long Island project.
- In 2005 and 2006, RBG Melbourne was a finalist in the Gardens Management category of the savewater! awards®.
Urban Landscape Water Management Research
The Royal Botanic Gardens has been dedicated to strategically improving landscape water management for over 15 years. It is important to provide this urban water management expertise to others through the internet, presentations, publications and workshops.
- Irrigation Association Australia May 2006 national conference presentation (PDF - 972 kb) - The development and evaluation of landscape coefficients to determine plant water requirements in the urban environment
- Irrigation Australia May 2008 National Conference presentation and paper Developing water management strategy for complex landscapes (WORD - 232kb)
- Irrigation Australia June 2010 National Conference presentation - Developments in soil moisture sensing for improved landscape water management
More water conservation information
Royal Botanic Gardens
Last updated 25 Oct 2011