Soils for nature

It’s important to know what sort of soil you have in your garden. This can help you work out what plants will grow best.

Sydney has many different soil types that fall in to two major groups:

• sandy soils, which come from sandstone
• clay soils, which come from shale or volcanic rocks.

Some soils may be a mix of the two. Some plants only grow well on one of these soils, whereas others will adapt and grow on both.

Soil pH is an important consideration for Sydney gardeners. Most soils in Sydney are acid (pH of less than 6.0). You can find out what your soil pH is with a simple test that you can buy from a nursery or hardware shop.

Soil colour is also important. Colour is a good indicator of drainage. Brighter subsoil colours like red, brown and yellow are usually associated with well drained soils. Dark browns usually mean the soil contains a lot of organic matter, whereas paler colours in the subsoil like murky yellow and grey usually indicate poor drainage.

Before you choose plants for your garden, find out what varieties suit your soil conditions. Read the label before you buy a plant as this usually includes information about soil type.

Looking after your soil and the life in it

Healthy soils are home to many soil animals including insects, invertebrates and worms that:

• help aerate our soils
• help water to penetrate more deeply
• eat fallen plant matter and convert it into nutrients for plants.

Microorganisms, including bacteria, fungi and tiny worms, are also essential for healthy soils. These organisms:

• help plants take up nutrients or change nutrients into a form plants can absorb
• help break down dead plant or animal matter
• reduce the likelihood of plant diseases.

If your garden has sandy soils, remember, these soils often:

• drain quickly
• have good aeration
• are usually low in nutrients
• may require more water
• suit many local native plants.

Many native species grow well in sandy soils including grevilleas, banksias, waratahs, hakeas or acacias. Adding organic matter and mulch is a good idea for all gardens, particularly sandy gardens.

Find out more about recycling household food waste into compost and worm farms.

If your garden has clay soils, these soils often:

• drain slowly
• hold more nutrients to support plant growth.

Healthy soil will have a balance of organic matter, invertebrates like worms and insects, microorganisms and fungi.

It’s easy to keep your soil healthy:

• Mulch your soil with leaves, bark or other types of organic matter to retain moisture, reduce weeds, improve water filtration, improve air circulation, nutrient availability for plants and provide food for soil organisms.
• Avoid pine bark – the invertebrates that break down organic matter don’t like it.
• Avoid using pesticides, fungicides and herbicides – they also kill the good invertebrates, fungi and microorganisms.
• Avoid working clay soil in your garden when it’s wet. This can compact the soil and damage the soil structure, making it more difficult for plants to grow.

Fungi – including mushrooms, toadstools and bracket fungi on logs – are important organisms that help maintain soil health. 

Many fungi work in a symbiotic or mutual relationship with plants to help them take up nutrients. In return, fungi get to access the nutrients in the plant’s roots. 

Avoid using fungicides to control problems like powdery mildew or black spot. You’ll kill the good fungi as well as the ones you don’t want. This means less healthy soil and plants. Dispose of infected leaves in a bin, don't compost them.

Record fungi you see and help put Sydney’s fungi on the Australian fungi map.

• Check your soil’s pH with a kit from your local nursery or hardware store. If your soil pH is too low or too acidic, you can increase it by sparingly adding agricultural lime or dolomite. If your soil is too alkaline you can reduce the pH by adding well-rotted manures and compost.
• Add organic matter and mulch to your soil.
• Don’t work or turn over your soil when it is wet, this will help maintain your soil structure.