TREES AND...
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Road-building rules (hard surface and quick draining of water) are the complete opposite to those relating to tree growth i.e. water and oxygen availability. Often, with roadside tree planting, maximum growth is inhibited by a hard compacted surface.
In addition the tree has no space to spread roots due to various obstacles (cables, water, drainage and sewer pipes, etc.) In principle 0,75 m² root space (substrate) per m² crown projection is needed. For street trees several factors are important when it comes down to soil: water, nourishment and air. Any disturbance of these factors can lead to serious growth and disease problems for a tree. Too little or too much water can affect a tree's growth. 10 to20 volume/percent water is necessary for optimum growth. Unfortunately many street and park trees receive no nourishment due to potentially valuable humus being lost when fallen leaves are disposed of, instead of being left to feed the tree's roots. The only way of closing this cycle of lost humus is to use compost bearing in mind that, of ultra importance for root development, good airing of the ground is important. The fact is that with many tree planting schemes its roots are strangled through lack of air in the ground. 20/40% volume of air is required plus sufficient oxygen i.e. more than 10% To achieve a good result especially in terms of town trees, a balance between nutrients, water and air is essential, It is important, therefore, to use a suitable mixture e.g. compost (10to20%) +soil in the space where the tree is to be planted. It is possible to mix compost with calibrated "tree" soil. Such mixtures are sold under the name "tree sand"
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