Monday, November 9, 2009

Wild & Windy Protection

In winter many gardens are ravaged by cold winds. Now's the time to plan for next year's planting of a windbreak or shelterbelt. In mild winter areas, it's still not to late to plant before the rains get too heavy. (We can only hope for rains that "get too heavy" in the 3rd year of drought in California.)

The shelterbelt's height should be 1/5th to 1/20th the distance to be protected. While a windbreak can reduce the wind's speed by 50% for a distance of up to 20 times its height, the best area of protection usually extends distance of about five to ten times the height of the windbreak. Plan your windbreak so that the mature size of the trees is sized to the area you wish to protect.

All windbreaks work best when their length is perpendicular to the prevailing winds. Shelterbelts needn't have a angled slope of short to taller trees to be effective. In fact, vertical, narrow windbreaks are usually the most effective in keeping the stronger winds lofted over the largest sheltered area. One row of the right tree is much more effective than wide, multi-row planting.

A completely solid windbreak causes some of the wind to whip up over the top and down to create a blustery vortex, like a sideways tornado, on the very side you're trying to protect. Allowing some of the air to pass through a windbreak makes the best diversion. A partially permeable windbreak allows some of the wind to slip through and form a gentle buffer of laminated air. This blanket of layered air helps to keep the blistery wind aloft after it passes over the top of the windbreak for a much longer distance than if there were no permeability. The most effective windbreaks are 50 percent permeable. (Not like the picture above. Taken at an uninformed suburban landscape.)

Other important considerations with windbreak designs include:

- Use evergreen trees for winter protection and deciduous trees when only summer buffering is required.

- The wind's speed is also reduced in front of the windbreak, the windward side, for a distance of two to five times the height of the trees. (This is a good place to plant young tree seedlings which can grow to be sturdy, well-rooted trees without the need of staking.)

- Don't leave any gaps in the windbreak as the wind will be funnelled through the opening at a speed up to 20 percent greater than its normal velocity.

- Make sure the windbreak is far enough away from the house to not cast a shadow on south-facing windows in the winter.

- Most edible trees make poor windbreaks, exceptions include: wild plums, Russian olive, Siberian peashrub and hackberry.

- Remember, the roots of the wind break are .5 to three times wider than the foliage and will compete for water and nutrients with other landscaping, water and feed accordingly.

- All the research and diagrams for windbreaks are based upon flat land. Those with hilly property will have to carefully observe the wind's patterns and plan carefully, predicting the wind's flow on complex topography can't be done without a $10 million dollar Cray computer.

Let me know what you think.

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