The previous section of this article on light illustrates how much shade is cast by a hedge or building. It is a trade off sometimes between casting a shadow and protecting the greenhouse from wind. The diagram below illustrates that a hedge will, on average, provide an effective windbreak for around ten times it's height. This is a much greater distance than any shadow it will cast, even in winter.

If you are designing a garden which is liable to strong winds, the best protection is not a solid structure such as a wall or wooden fence. These cause the air striking them to be deflected above the fence at speed, only to descend at a short distance later. The best structure for wind protection is a windbreak such as a hedge.

A hedge will let around 50% of the air pass through it, slowing it's speed as it does so. The remaining air will be more gradually deflected upwards and will not reach it's previous speed until a good 10 or 12 times the height of the hedge later.

A hedge used as a windbreak needs three key qualities:

1. The correct density of foliage and branches
2. The ability to survive well in windy conditions
3. Be evergreen in order to provide winter protection

Hedges which fit these criteria include Privet, Yew, Holly, and many of the Conifers. These hedges will need regular cutting to avoid them becoming too tall and therefore casting too much shade.

 

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