Controlling Exposure to Toxic Chemicals, Smoke and Pollutants with Windbreaks

Plants can be used as windbreaks, hedges or screens to form a living, physical barrier.  You can also construct windbreaks from timber, cement, etc which will give you instant shelter and a chance to establish small wind tolerant species.

There are many reasons for creating a plant barrier:
  • To filter unwanted air borne chemicals (such as pollens, smoke, pollutants) that can affect health and wellbeing. To collect dust from the atmosphere that is consumed by bacteria on the leaves.
  • To increase oxygen levels in the air
  • For privacy – a row of plants provides privacy from neighbours and the street.
  • To improve your outlook – a row of plants can block out your view of unsightly areas.
  • To control noise   this is done best in conjunction with an earthen mound. A single row of plants might not stop much noise.
  • To control wind and temperature, eg. to minimise the effect of hot, dry winds.
  • To form a microclimate so that species can be grown that would not normally survive.
  • To provide a physical barrier, eg. to contain animals and children.
  • To create a visual barrier within the garden, eg. a low hedge enclosing a rose planting.   

What is a Windbreak?
A row of plants used to slow or deflect the wind is known as a windbreak. The plants in the windbreak may have dense foliage that deflects or stops most of the wind, or open foliage and branches that allow some wind through but at a greatly reduced velocity.

HOW DO WINDBREAKS WORK?
Windbreaks function by directing wind upwards and away from the area that needs shelter.

When designing and planting a windbreak consider the following points:

  • Reduction in wind is determined by the height and width of the planting.  Wind velocity is reduced for a distance from the windbreak of about 5 to 10 times the height of the planting.
  • If you have a vertical windbreak such as a cement wall, the wind will rise directly upwards, but will then drop very quickly back down on the other side of the wall.
  • Dense plantings will provide greater wind control, however very dense plantings may have the opposite effect by creating an area of turbulence immediately behind the windbreak. For this reason, it is best to create a windbreak that allows some wind to filter gently through the planting.
  • Two or more rows of planting will give greater protection. Two or three parallel rows of plants of different heights can be very effective in reducing wind velocity (ie. plant a row of shrubs in front of a row of taller growing trees).
  • For large exposed areas (eg. farm paddocks), staggered plantings are effective. 

The best windbreaks
The most effective windbreaks are made up of several layers of plantings (with some spaces between them) starting with low shrubs and working up to tall trees.  This sloping wall of vegetation will gradually push the wind upwards and allow it to come back down a long way away with little turbulence.  Some of the wind will pass through the windbreak, which reduces turbulence – this is why it’s important not to plant too densely.

QUICK WINDBREAKS
If you don’t have the time to wait for plants to establish in a windy spot, you can always construct a fence, wall or trellis in the short term.  If you’re building a windbreak, then the principles are much the same as if you were planting one.  Solid walls will only offer limited protection, as the wind will be “dumped” down on the other side of the wall.  A porous barrier such as lattice or an open-weave fence that filters and slows the wind will be more effective.

CHOOSING WINDBREAK PLANTS

When you choose plants for a windbreak, you should plan ahead and think about what the plants will be like when they are full established.  Think about the following points:

  • Choose plants that suit your climate and soil – seek advice from a local nursery person.
  • Find out whether the plants need regular clipping to keep them dense.
  • Include fast-growing plants (eg. wattles) in the windbreak, as well as slower-growing long-lived plants.  The fast species will do the job in the short term while the slower species will take over later, and live for longer.

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