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Plant and Soil Communities

As gardeners we tend to forget that many plants will only grow in a particular soil and climate area. We deal with the plants that have been bred especially to be generalists, or to grow in the range of garden soil types that may not resemble natural soils. A plant from the nursery comes home, often with little thought as to its original home, and we hope it grows. Or if we really hope it grows, we manipulate garden soil to resemble natural conditions, mimicking drainage or nutrient levels.

Another aspect of Australian plants is that the history of using them in a garden situation is measured in decades, not thousands of years of cultivation as for many European plants. Wheat and seed grasses have been manipulated by growers for thousands of years, and even fruit trees were being grown by the Romans and then British monasteries to produce the fruit we know today. The advances in propagation and nursery practice today have made many plants a lush, juicy and flowery version of their earlier selves.

However, many plants are found only on particular soil types, and may never be suitable for garden use. The best way of seeing different plant communities is to drive through bushland observing both road cuttings (rock and soil) and the associated plant community. By keeping a careful eye on both, it is interesting to see how the plants change with topography and soil type.

On a trip to Rockhampton, QLD I had the opportunity to see plant and soil communities close up. Rockhampton is on the tropic of Capricorn. Many plants such as the abundant palms were different from Victorian species, but there were many familiar eucalypts, melaleucas and casuarinas.

One plant community grew only on a serpentinite rock derived soil, which is high in nickel and magnesium. It consisted of 5 tree types including acacia, iron barks, and melaleucas, and a mid story of numerous grass trees and smaller acacia. The ground level had 12 different types of grass and succulents, including many germinating grass trees. One special plant was a small blue flowering shrub, stackhousia tryonii which absorbs nickel into its system. This is known as hyperacculmulation, and nickel concentrations can be 400 times higher in this adapted plant than another nearby species.

Other plant-soil associations seen included a certain acacia growing only on granite, and QLD gums such as brigaloo and coolabah growing on basalt. Also interesting were the samphires, a group of succulents (some are edible) that grow on salt pans, and are one of the few plants to tolerate extremely high salt levels. Mangroves will only grow in tidal flats, where each species has a different preference for the amount of time their roots are submerged. Others such as casuarinas and acacias were very tolerant, and grew well almost anywhere.

Stay tuned for more Tales from the Potting Bench. If you would like to see a particular topic in a post feel free to email me. Click here to email 

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