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A THOUSAND or more Eucalyptus mannifera for the tramway have arrived at the Yarralumla Nursery.
They are potted in rigid, 400mm plastic pots, of which I understand will be progressively potted on into larger pots for eventual planting in 2018.
I’m not going to discuss here the poor choice for this project, but why when they decided to contract the growing of these trees, are they being grown in rigid pots?
Some years ago, Yarralumla Nursery found a better way of growing eucalyptus. Because of the nature of the eucalyptus root system, they started using Spring Rings to overcome the problem of trees becoming root bound in rigid pots.
In a rigid container there is no alternative but for the roots to grow in circles. When planting out, either the circling roots have to be disentangled or pruned and neither is a good solution.
Circling roots provide no stability with the result, particularly in a wet year, of the possibility of trees toppling over.
A Spring Ring is a length of heavy duty plastic of various widths, perforated by hundreds of holes with the undulating surface raised, similar to an egg carton. The plastic is formed into a circle and held in position with clips, but no base.
The Spring Ring is placed on plastic sheeting and filled with potting mix to which the tree is planted. As the fine roots develop they grow through the myriad of holes to the outside of the container. These shrivel in contact with the air, known as air pruning.
Rather than thick roots circling inside the pot, a mass of fine roots develop evenly throughout the potting mix.
The mass of fine, healthy fibrous roots mean a better uptake of nutrients leading to faster growth and healthier plants.
This growing method has been acknowledged by expert wholesale tree nurseries around the world and, for example, only trees grown this way were specified for the landscaping of thousands of trees at London’s Olympic Park. They have been used and specified for more than 10 years by the Royal Botanic Gardens at Kew and the Edinburgh Botanic Gardens
From Holland to Germany and Italy the major tree growers all use Spring Rings.
One of the largest growers of advanced trees in the UK is Majestic Trees, which grow thousands of advanced trees from one metre to a massive 12-metres tall, weighing up to eight tonnes. Their trees are grown in Air-Pots. When advanced trees are provided for such projects as the Thames Embankment in London, they cannot be allowed to fail by being grown in the wrong container.
So the question is, with all the expert advice available, did the Yarralumla Nursery not specify these eucalypts to be grown in Spring Rings?
They have in the past made extensive use of Spring Rings and yet all these eucalypts were grown in rigid pots? Travelling in the tram could be a hazardous ride!