The Big Phosphorus Issue - Australian Native Plants

Using Australian native plants in the home garden is one of the true joys of gardening in our sun-baked country. However, many gardeners are often discouraged from using native plants because they have a reputation for being fussy and think they need to be kept separate from exotic plants in their garden. While this is true for some native species, many can be treated as regular garden plants. The reason they have acquired this reputation is that some native plants are sensitive to phosphorus. Understanding this distinction can make using natives in your garden easy and rewarding.

Acacia terminalis

What is phosphorus?

Phosphorus is an essential nutrient in soil, vital for plant growth. It is a fundamental element in plant cells and plays a critical role in cell division and the development of new shoots. This makes phosphorus especially important for the growth of seedlings and young plants. It can be sourced organically or applied through chemical fertilisers.

Why don’t. Australian natives like phosphorus?

A few, but not all, Australian native plant species are sensitive to phosphorus. Rather, they have evolved to be highly efficient at extracting the limited phosphorus available in native soils. Plants within the Proteaceae family (such as Banksia, Grevillea, and waratah) have developed specialised ‘hairy’ roots called "proteoid roots" through the process of evolution. These roots spread out in a fine mass, allowing the plant to absorb nutrients from Australia’s ancient, nutrient-depleted soils. When overloaded with phosphorus, these plants struggle to cope, often suffering and eventually dying with sustained exposure. On the other hand, the majority of Australian natives can thrive in richer soils containing higher levels of phosphorus.

Which Australian natives are phosphorus sensitive?

Generally speaking, if grows on coastal heathlands, sandy/sandstone soils or arid soils, generally it will be sensitive to excess phosphorus. Plants growing in rainforests or wetter areas are likely to be more tolerant of phosphorus in their diet. Herbaceous natives also seem to be more forgiving to higher phosphorus levels.

Phosphorus sensitive natives include but are not limited to: Many Acacias, Banksia, Grevillea, Daviesia, Hardenbergia and Kennedia.

Why is this important?

Understanding how phosphorus affects Australian native plants is crucial for effectively fertilising and maintaining your native garden. This knowledge is also important when planning your garden. For example, if you want to incorporate Australian natives into your existing exotic garden, it’s advisable to choose natives that are tolerant of phosphorus-rich soils and fertilisers to avoid overfeeding them. Additionally, when designing your garden and selecting plants, you might consider creating a section specifically for phosphorus-sensitive plants, allowing you to manage them with low-phosphorus fertilisers, thus avoiding potential issues. Just as you would group plants with similar light or soil requirements, phosphorus sensitivity is another factor to consider in your garden planning.

Much of this can be avoided when you choose to fertilise your garden with organic inputs Read my comprehensive guide to organically feeding natives.