Saving water with automatic irrigation systems.
Your irrigation system needs to provide you with the flexibility to alter the time and duration of watering for various seasonal conditions. In Adelaide it is preferable to water early in the morning. Since we have distinct seasons we need to alter our watering accordingly. It is futile to attempt to water the garden by hand. The time required to water effectively is beyond the majority of working people. Automatic watering systems are a necessity. However they need to be programmed properly or they can waste huge amounts of water.
It is also important to use good quality sprinklers and drippers.
Water conservation through soil preparation.
The most important part of water conservation in the garden is soil preparation. On Adelaide's soils it is vital to create a well drained soil that retains water at depth. Treatment of the clay soils varies from that of sandy soils but putting 100mm of sandy loam over them is definitely not the way!
Poorly trained and unskilled landscapers often install gardens over thin layers of imported loam. This is a recipe for high water use and poorly growing plants.
Once the soil has been properly prepared and the plants are in the next most important step is to mulch. Most people (including some landscapers) put mulch on too thinly and fail to maintain it. Again this costs money through evaporation of water.
Most plants need a depth of 300mm of well drained soil to grow well. Ideally the soil should be aproximately 40% clay, 40% sand and 20% organic material with air and water spaces. Most of the Adelaide plains has an alkali clay based soil and the coastal strip is sand or sandy loam. The Adelaide Hills are largely acid clays.
To improve clays we need to add sand and aged compost. To improve sandy soils we add aged compost because it is nearly impossible to add clay to sand.In practical terms we add 100mm of sand and 50mm of aged compost over the clay soil and dig in to a depth of 300mm. On sand we add 100mm of aged compost and dig in to the same depth.
Finally the improved soil is rotary hoed and you are ready to plant. Planting holes should be the same depth as the potting mix the plant comes in but should be aproximately twice as wide as the pot. This will give the roots an easy time as they grow outwards.
Once the planting is complete we need to add carefully selected mulch at a depth of 35mm-50mm. It is important to select the appropriate mulch for your plants. The wrong mulch can accelerate evaporation of water from the soil which is completely the opposite of what we need.
Watering by automatic system twice a week with supplementary hand watering in the first two to three weeks will be sufficient. After that you should be able to water once a week or even less automatically with hand watering of individual plants if they wilt. On clay soils and sloping ground the most effective way to water is pulse watering. A rule of thumb is that you want to apply one hour of water. However if you apply it continuously you get massive runoff from slopes and an impervious layer can develop on flat ground. I recommend that you water early in the morning. Apply water in ten minute bursts separated by twenty five minute breaks. Naturally you need an automatic system to set this up.Once the garden is fully established it should be possible to water as little as once per month for most of your drought tolerant plants and once per fortnight for your more sensitive plants.