BUSTING THE MYTHS: Myth #2 You can’t fertilise Australian native plants

All plants require a good balance of nutrients in the soil to thrive and native plants are certainly no exception.

Native plants have adapted to thrive on our older (low nutrient) soils and work in conjunction with soil bacteria to utilise all available nutrients. It is more important to have a healthy, living soil than to rely upon chemical fertilisers which detrimentally affect soil bacteria. If your plants are showing signs of nutritional deficiencies you are better off to use organic or slow release fertilisers which present minimal threats to soil bacteria. To promote a healthy soil you are better off to apply mulch to the top of the soil which slowly breaks down and improves the soil structure over time. Avoid incorporating mulch and other organic matter into the soil when planting native plants. This practice is best left to your vegetable garden.

The myth that you shouldn’t fertilise natives plants usually stems from the fact that some natives prefer lower concentrations of Phosphorus. Species that prefer low Phosphorus fertilisers are generally those from the Proteaceae and Mimosoideae families such as Waratahs, Grevilleas, Banksias, Wattles. These plants naturally occur in Phosphorus-impovorished soils and are extremely efficient at utilising the small amounts of available Phosphorus. Many of these species develop “proteoid” roots so excess amounts of Phosphorus in the soil can become toxic to these species.

Other native species such as Callistemons, Melaleucas, Leptospermums don’t mind higher amounts of fertiliser in the soil.

So how should we fertilise our native plants?

Check the NPK
When using fertilisers on Phosphorus-sensitive plants, check the NPK ratio (Nitrogen, Phosphorus, Potassium) and make sure the Phosphorus (P) level is 3% or lower.

Use Slow Release Fertilisers
Slow release fertilisers (which include organic fertilisers) release the nutrients gradually in a measured dose. Avoid using heavy duty chemical fertilisers as they kill soil bacteria and can also cause chemical imbalances in the soil that lock up nutrients so that they become unavailable to plants.

Be careful of soil improvers
When using soil improvers such as lime or dolomite, be careful as it can raise the pH of the level to be too alkaline for many natives and will prevent them from being able to utilise the nutrients in the soil. If you do want to improve your clay soil, gypsum is a better alternative as it won’t affect your soil pH

Manures and Compost
Chicken manure is high in Phosphorus and should be avoided on Phosphorus sensitive plants. Mushroom compost should be avoided as it raises soil pH and can kill soil bacteria. As a rule of thumb we generally discourage using manures and compost around natives as it is difficult to attain how much nutrient will be released.

Seaweed
Applications of Seasol or equivalent are beneficial for improving the soil biology by encouraging micro-organisms.

In summary:

• Natural soils are good and over stimulus of soil sometimes leads to problems
• A healthy soil is a balanced soil
• Organic matter is best applied to the surface of soil rather than incorporated into it.
• Before applying fertiliser to your plants, assess whether your plants actually needs it. Visual assessment of the leaf will indicate requirements.
• Choose species that are appropriate to your soil type. If you need help in selecting plants or assessing your site conditions consider a consultation by Wariapendi.