LIKE many enthusiastic gardeners, when we moved to our present home we enthusiastically began to renovate the existing garden and to plant many Australian plants.
Out came plants beyond their use-by date, and in went banksias, grevilleas and more.
Many of our new plants in one particular garden bed were dead in less than a year. Leaves yellowed, and almost overnight, some died. In other parts of our garden most plants thrived. The reason for the deaths in that one particular garden bed lay in the history of the soil.
We recalled that there had been roses that were replanted in a friend’s garden.
We made an educated guess as to what fertilisers had been applied over the years. Mystery solved. Most fertilisers available commercially contain a higher amount of phosphorus than some Australian plants can manage.
These particular plants have evolved with specialised root systems which can extract sufficient phosphorus for the needs of the plant.
They originate from areas with poor soils which contain very low amounts of phosphorus.
These specialised roots (called proteoid roots) are found in plants such as banksias, grevilleas and hakeas. This group of plants belong to the Proteaceae family. They still require small amounts of phosphorus to grow well, they just don’t need too much.
Many Australian plants are not susceptible to excessive amounts of phosphorus, but it’s wise to choose low phosphorus slow-release fertilisers.
Check the NPK analysis - the P level should be three per cent or less.
If you are establishing a new Australian plants garden where there may have previously been plants that were regularly fertilised, it’s a good idea to select plants that are not phosphorus-sensitive.
There is plenty of choice – a few suggestions are native peas, daisies, brachychitons, kangaroo paws, eremophilas, bottlebrushes, correas, croweas, small eucalypts, wattles, tea trees, westringias.
CHECK YOUR SOIL: Many Australian plants are not sensitive to phosphorus.
DISTINCTIVE PLANT: Use a low-phosphorus fertiliser on banksias.