Catch and conserve water
In his new book, The Sustainable House Handbook, JOSH BYRNE provides a wealth of tips for designing an energy-efficient and waterwise house and garden, using his own home in Perth as a model. In this edited extract, Josh discusses permeable surface treatments, and how hydrozoning and soil conditioning can help you capture and use water efficiently
Stormwater is rainfall that hits the ground. In urban areas, where the ground surface is largely impervious because it is covered by asphalt, concrete and paving, stormwater is directed to drainage basins and waterways to prevent flooding. In the process, it collects pollutants, such as nutrients from fertiliser, and hydrocarbons from car tyres, oil and fuel residue.
If you intercept stormwater close to where it falls, you slow the transportation of contaminants and reduce the size of the downstream infrastructure required to mitigate flooding. Enabling stormwater to infiltrate the ground supports deep-rooted vegetation, which, in turn, helps to shade and cool the surrounding environment.
With that in mind, our garden in Perth has been designed to act like a sponge. We’ve kept paving to a minimum, and favoured permeable surfaces that allow rain to quickly penetrate, replenishing soil
LEFT
Josh has favoured using permeable surfaces, including gravel paths, in his Perth garden to significantly reduce stormwater run-off. moisture and recharging the underlying aquifer we rely on for irrigation. Permeable surface treatments include decking with spaces between the boards to allow water through, and pine bark and gravel paths.
We’ve also used gravel for the driveway. To render it suitable for vehicle traffic, lightweight recycled plastic drainage cells were installed to make the surface secure while minimising compaction. The drainage cells, which lock together, were installed over a geotextile fabric liner that allows water through but prevents the cells and gravel sinking into the sand. The cells were then filled and covered with locally sourced coarse gravel. In addition to allowing water to penetrate, the gravel driveway was quick to install (it took less than a day), was similar in cost to mid-range paving, and looks great. We can also hear people coming as they walk towards the house.
water management
Once you’ve captured your water, be it rainwater, greywater, groundwater or mains water, the next consideration is how you use it. Plants have various water
needs – native plants, for instance, have very different needs to lawn, fruit trees or vegetables. Hydrozoning involves grouping plants in the garden based on their common water requirements. Each hydrozone can be serviced by a separate irrigation station (or multiple stations, depending on the zone’s size) to enable tailored and efficient watering.
Importantly, in each irrigation station you can use an irrigation emitter best suited to that group of plants. By using the same emitter type in a zone, and distributing the emitters to provide uniform watering across the zone, it is possible to accurately set an irrigation run time to water a particular plant group without under- or over-watering.
We have the following hydrozones and irrigation emitter types in our garden:
Vegetable garden Irrigated with groundwater using substrata drip line.
Fruiting and ornamental exotic trees Irrigated with groundwater using substrata drip line.
Turf Irrigated with groundwater using rotary sprinklers.
Containers Irrigated with groundwater using spray stakes.
Greenhouse Irrigated with groundwater using misting sprinklers.
Perennial plantings Includes a mix of herbs, shrubs, small fruit trees and vines; irrigated with greywater (with top-up capability using groundwater) using substrata drip line.
Native plantings Irrigated with groundwater (for establishment and dry periods only) using substrata drip line.
There is a deliberate correlation between the water requirements of the hydrozones and their size – the largest zone (native plants) requires the least water, while the high-water-use zones are kept small and intensive. Planted areas requiring irrigation are evenly balanced with areas of decking, gravel and mulch pathways that don’t
need water. Importantly, these areas are shaded so as not to create hot spaces, and are bordered by plantings to create the perception of lushness.
soil conditioners
To improve the water-holding capacity of our sandy soil, we’ve added soil conditioners. Generous amounts of compost were initially applied to garden beds to increase the organic matter.
This approach is beneficial for all soils, including clay, where it helps to improve structure and boost microbial activity. We’ve also added bentonite clay to the vegetable garden and fruit tree areas to further improve water and nutrient retention for these hungry plants.
We mulch all areas regularly to keep the plant roots and soil life cool, retain moisture and suppress weeds. In most areas, coarse pine bark mulch with irregular particle sizes is used, as it allows rain and air to pass through and is less likely to blow away. Pine bark mulch is also long-lasting.
Lupin mulch, which is made from the by-product of local lupin crops, has been applied to the productive areas, including the vegetable beds and fruit trees, where it is an excellent source of organic matter for building up soil and providing hungry plants with nutrients. Lupin mulch breaks down quickly, so it needs to be topped up regularly and is best for protected areas.
Other suitable mulches for these types of plants and protected productive areas include lucerne, pea hay and sugarcane mulch. As always, it makes sense to use products that can be sourced locally.
We apply pelletised poultry manure and rock-mineral-based trace elements to productive and exotic ornamental plantings on a seasonal basis, and continue to improve the soil with homemade compost. The vegetables and fruit trees receive regular applications of liquid kelp and fish emulsion, however, the native garden beds don’t receive regular fertilising now that they are established.