Waterwise garden hub
Discover waterwise tools and expert advice tailored to WA gardens for the warmer months ahead.
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Improving your soil
In this article
- The importance of good soil and mulching
- The best way to mulch your garden
- How soil types vary across regions
Good soil is the foundation of a healthy waterwise garden. The healthier your soil, the more drought resistant your plants will be.
Improve the soil every time you dig
Sandy soil, commonly found in WA, has low water and nutrient holding capacity, which isn’t great for gardens. While many of our local native plants have adapted to our soils, they still benefit from improved soil health. The ideal soil type for most exotic plant species is a loam, made up of clay, silt and sand. It slows water movement through the soil, allowing more absorption for plants. You can mimic a loamy style soil and enrich your garden by:
- Adding clays to improve water and nutrient holding capacity.
- Adding compost for healthy plant growth.
The best time to improve soil is before you plant a new garden, preferably in late autumn. If planting a new garden, make sure the organic matter is thoroughly mixed through the top 30cm of soil for mass planting areas. When planting individual pots, mix organic matter with the existing soil that immediately surrounds the root zone. As a general ‘rule of thumb’ dig a hole twice the depth and width of the pot and discard a third of the existing soil and thoroughly mix in organic matter before planting. Improved soil encourages roots to establish quickly. If planting into an established garden bed, use the individual pot planting method.
Follow the tips below to create a healthier garden from the root up.
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Mulch is like sunscreen for your soil
Applying mulch to your garden can greatly reduce evaporation loss, improve the soil, reduce weed growth and improve the appearance of your garden. Applying a generous amount of waterwise mulch can help you save up to 20% of water in the garden.
Tips for mulching your garden
To help your garden thrive:
- Apply between 5–10cm of good waterwise mulch across the surface of the soil, keeping it away from plant stems.
- Choose a chunky coarse mulch for general shrub and tree garden areas. Chunky mulches allow water to reach to the soil surface and shade the soil, keeping plant root systems cool.
- Choose a composting mulch, such as straw and lucerne for vegie gardens and more delicate plants. These mulches break down and increase soil health over time, which results in healthy plants.
- Ensure mulch is from an accredited supplier and is certified weed, pest and disease free.
- Choose waterwise approved products displaying the Waterwise and Smart Drop Certified symbols.
For more tips on mulching watch this video:
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Wetting agents do wonders for your soil
Sandy soils are known to be water repellent (hydrophobic), making it a challenge to maintain a healthy garden in WA. The simplest way to improve the absorption of water in your soil and help it spread more evenly throughout is to add a wetting agent.
When should I apply wetting agents?
Always apply granular or liquid wetting agents at planting. Apply again at the start of winter, early spring (to ensure spring rains soak into the soil) and early summer. This helps your soil retain water and nutrients and minimises runoff and water wastage. Wetting agents require activating by watering in.
Watch this video to learn more about how wetting agents can improve your soil profile:
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Test your soil
Soil pH impacts the availability of minerals and nutrients for plant uptake and growth. Nutrient deficiencies in plants are often the result of pH problems (either too acidic or too alkaline) rather than insufficient fertiliser.
A simple pH test can help set up your garden for success, as well as save you time and money. You can buy a home testing kit from garden centres.
The ideal soil pH for most grasses and plants in Western Australia is fairly neutral at 6.0 - 7.0. Soil pH variance is best corrected before planting. If you already have an established garden or are unable to adjust your soil, there are a range of plants that can thrive in more hostile soils. Seek specialist advice at your local Waterwise Garden Centre.
Soil characteristics
Soil types across WA vary greatly. To keep your soil healthy, it's important to understand the soil characteristics of your garden. While some local native species of plants will grow in natural soil without any soil improvement, all still benefit from it, especially during the establishment phase. Planting most species in the regions will require some level soil improvement before planting in a home garden situation.
| Soil type | Becomes non-wettable | Water holding capacity | Nutrient holding capacity | Benefits from organic matter | Benefits from soil amendments |
|---|---|---|---|---|---|
| Sand | Very commonly | Poor | Poor | Greatly | Greatly |
| Sandy loam* | Occasionally | Medium | Medium | Greatly | Some |
| Clay | Very rarely | Good | Medium | Greatly | A little |
| Rocky or stony soils | Occasionally | Medium | Medium | Greatly | A little |
| Potting mix** | Very commonly | Good | Good | N/A | A little |
**Potting mixes are formulated for pots and not suited for garden beds.
Soil types in the South West vary greatly. Common soils include the deep sands on the coast to sandy peats, bare rock, gravel, loams and clays, and complex duplex soils where one type sits on top of another.
Soils in the Great Southern Region vary from deep sands to sandy peats, loams and clays and complex duplex soils where one type sits on top of another.
Soils in the Mid West region range from deep sands on the coast to sandy peats, loams and clays, and complex duplex soils where one type sits on top of another. There are also areas of rocky stony soils.
Soil types in the Goldfields region include sand, gravel and clay, with the most common combinations being sandy loam and loamy clay.
The area around Kalgoorlie is undulating plains on granite, which have areas of calcareous loamy earths with red loamy earths, red deep loamy duplexes and red shallow loamy duplexes. In some town gardens, the soil cover over rock is shallow and can have a limiting effect on root development.
The most common natural soil types in the Pilbara are sand, sandy loam and rocky stony soils. In some areas the soil is strongly alkaline with a pH level of 9 or above.
The most common soil types within the Kimberley town boundaries vary from sand, sandy loam and rocky stony soils. Black cracking clay is also common.