Symbiotic associations between plant roots and fungi. The fungal network dramatically extends the plant's effective root system, improving water and nutrient uptake (especially phosphorus). Found in most healthy soils.
Mycorrhizal fungi form intricate networks around plant roots, essentially extending the root system's reach into the soil. The fungi receive carbohydrates from the plant through photosynthesis, while the plant benefits from the fungus's superior ability to absorb phosphorus, nitrogen, and other minerals from soil that the roots alone couldn't access. This relationship is particularly valuable in Australian gardens where many native soils are naturally low in available nutrients.
Two main types exist: arbuscular mycorrhiza (AM), which penetrate root cells and work with most garden vegetables and ornamentals, and ectomycorrhiza (EM), which form sheaths around roots and associate with many Australian native trees and shrubs. Mycorrhizal fungi are especially important in drier climates across zones 9-12, where they help plants cope with water stress by improving soil structure and water retention.
To encourage mycorrhizal activity in your garden, avoid excessive soil disturbance, reduce chemical fertiliser use (which can inhibit fungal growth), and incorporate organic matter like compost. Many native Australian plants have evolved strong mycorrhizal relationships, making them excellent choices for low-maintenance gardens. You can purchase mycorrhizal inoculants from Bunnings or specialist nurseries to introduce fungi when planting, especially useful in heavily cultivated soils or when establishing new garden beds.