Protection from Pollution

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The Scarboro Garden Scene
Protection from Pollution
Hedges, shrubs and trees all play a big part in reducing the transportation of airborne pollutants. According to the Royal Horticultural Society’s magazine, “The Garden”, particulate pollution causes about 4 million premature deaths worldwide per year: we in Calgary are very fortunate in that we suffer relatively little from this problem, but the edges of the Scarboro community clearly have more of a problem than the interior.

Plants with large, dense canopies and rough, hairy leaves are especially effective at catching particulate pollutants

reports an article in December’s RHS magazine. This applies to all shrubs and trees, but with our long winters, evergreens are very effective. Fortunately the protective barrier can also be an attractive component of our gardens. To be effective, hedges should be a metre high and a metre wide, but for many of us that is too much space to provide to this end – but a good compromise is to have a hedge that appeals to our eye, with a secondary line of defense consisting of shrubs interior to the outer hedge – hardy roses and other colourful shrubs are ideal, but dense evergreens would be better; light pruning of the shrubs will create denser foliage.
Caragana bushes are not in favour with people concerned with keeping alien species out of the prairie environment, but when controlled, they do help as windbreaks. A much more benign barrier can be produced by cotoneaster hedges, even those damaged by oyster scale quickly grow back after being treated effectively.
Small evergreens that collect airborne pollutants include dwarf mugo pines, junipers, Russian cypress and yew. William Reader, creator of Reader Rock Garden, planted spruce trees as a windbreak, and planted two lines of spruce with the second line offset from the first, in order to reduce wind velocity. Looking at hedges (and park fences) in Scarboro it is easy to see which direction our most frequent winds are coming from, and where we can best focus our efforts.
Cedars are densely cloaked in needles: they will trap small particles very effectively – I love the look of them, but as many of us have found out, growing them successfully depends so much on luck and location: they should probably not to be planted in windy western exposures.
Feb 12