Every so often you come across an idea that challenges conventional wisdom yet leaves you marvelling at its simplicity. I came across such an idea recently and have become convinced that it has the potential to revolutionise the establishment of an extensive range of trees and shrubs in all sorts of situations where they would struggle or probably perish. The technique has been christened 'long stem planting' by a very innovative electrical engineer by the name of Bill Hicks who has spent the last fifteen years turning on their head long held laws for the establishment of a very wide range of Australian trees and shrubs. Whilst this technique was pioneered for environmental restoration projects it has also been highly successful in garden situations where it has been trialled.
One of the basic laws of gardening is that when it comes to planting trees and shrubs that the plant must end up at the same level that it had been at in its pot. The consequence of burying the crown of the plant is usually suggested to be that it will succumb to crown or stem rot and be dead within a very short time. Bill Hicks became involved in an environmental restoration project in the NSW Hunter Valley where willows were being planted to prevent the erosion of riverbanks. Whilst willows were very good at solving the erosion problem Bill was alarmed at their invasive nature and their long term weed potential. Bill questioned why indigenous species could not be used instead of willows. The consistent answer he received was that they would wash away in the next flood before they could establish enough to stabilise the bank. Bill suggested simply planting native seedlings much deeper and was met with the conventional wisdom that this would be a waste of time. One to one and a half metre high seedlings of various species of Acacia, Eucalyptus, Callistemon, Leptospermum and Melaleuca have been planted up to a metre deep using a water lance. The system has proven itself to be consistently successful in not only providing greater survival and establishment of plants, but also in preventing the erosion that led to the use of exotic species such as willow that have since become a weed problem. Bill’s work has also inspired a range of other horticulturists to test the technique in other environments and with vastly different groups of woody plants
The long stem planting technique first developed by Bill Hicks has been adapted to a variety of other environmental projects around NSW with vastly different species and in all sorts of soils and microclimates. At one extreme Sydney Golden Wattle (Acacia longifolia) shrubs deep planted into coastal sand dunes have shown much higher survival rates in a situation where there was minimal maintenance of the plantings. On the other hand a trial conducted in a rainforest regeneration project on the NSW Central Coast showed similar promising results with species such as Sandpaper Fig (Ficus coronata), Cheese Tree (Glochidion ferdinandi) and Plum Pine (Podocarpus elatus). Extensive root systems that had formed on the buried stem areas were observed when samples of trees from both projects were dug up to try and establish why the plants were establishing so well.
The success of long stem planting results from the ability that many woody plants have to form what are known scientifically as adventitious roots (a term for roots that emerge from an area of the plant where they would not normally be expected to form). Gardeners are familiar with such roots because they are the type of roots formed when you successfully strike a stem cutting. One of the most astonishing results I saw in researching this story was a group of Sydney Blue Gums (Eucalyptus saligna) in a garden situation. Dozens of tree seedlings planted about 30cm deep had grown up to 5 metres in height in less than a year. None of the seedlings was watered in when they were planted yet the survival rate was over 95%.
There appear to be a number of reasons why the technique often achieves quite spectacular results. The most obvious one is that the plant forms a much more extensive adventitious root system that complements the original root ball formed in the pot and gives a much greater surface area to take up water and nutrients from a more extensive part of the soil profile it is planted into. The extra root system would also replace any curled or girdled roots that may have formed in the pot. The greater planting depth also puts the initial root ball into a part of the soil profile that usually has a reservoir of moisture that does not dry out as readily as at the soil surface.
It should also be said that some failures have occurred with the technique. Woody species that do not readily form adventitious roots have struggled, as have plants put into very adverse soil conditions such as compacted, heavy clays or soils that are prone to waterlogging.
The range of experience with long stem planting for environmental restoration has consistently demonstrated the potential of this idea for situations where limited watering and weeding is possible. As well as giving environmental restorers a powerful new tool to help establish trees and shrubs, this technique also holds amazing promise for gardeners as well.
Further information:
• Rehabilitating Australina streambanks with longstem native tubestock
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