Windbreaks and hedgerows: shelter, habitat, and food

Shelter is a design decision

On open ground, the wind is the loudest thing on the land. It dries soil, drifts snow, chills animals, and pulls heat out of houses. A well-placed line of trees and shrubs doesn't stop the wind. It slows it down and spreads it out.

The USDA National Agroforestry Center lists what that buys you: better crop yields, snow spread more evenly for soil moisture, fewer livestock losses from cold, and lower heating costs for farmsteads.

How a windbreak bends the wind

Windbreak design is measured in H, the height of the trees. University of Nebraska–Lincoln Extension, in a guide sponsored with USDA, explains that a windbreak slows the wind for 2 to 5 times its height upwind and up to 30 times its height downwind. For 30-foot trees, that's up to 900 feet of calmer air.

Density matters more than most people expect. The same guide says a windbreak that blocks 40 to 60% of the view gives the largest protected area and excellent erosion control. Below about 20%, it does little. Above about 60%, it starts to create turbulence behind it. Gaps are worse than nothing: they funnel wind through faster than in the open.

Design for your goal

The USDA Natural Resources Conservation Service sets design standards for windbreaks, Conservation Practice Standard 380. It defines the protected zone as 10H downwind and 2H upwind, measured by the tallest row at 20 years old, and asks that windbreaks run perpendicular to the problem wind. The density it calls for depends on what you're protecting:

• Spreading snow evenly across a field: 25 to 50% density, with windbreaks no more than 20H apart.
• Catching snow before it reaches a road or yard: at least 50%.
• Sheltering livestock: at least 65%.
• Cutting heat loss from a home: over 50% on the windward side.

Rows, length, and placement

For a farmstead, the Nebraska guide describes two or three rows of conifers, one or two rows of tall hardwoods, and at least one row of shrubs. A windbreak should run unbroken for at least ten times its height. NRCS adds that short "legs" at right angles to the main row help when the wind shifts.

NRCS farmstead guidance recommends planting on the north and west sides of the home, set back 2 to 5 times the height of the tallest tree, or 100 to 200 feet where snow is heavy, with rows about 15 to 20 feet apart.

What it's worth

Studies cited by NRCS found that windbreaks can cut winter fuel use by 10 to 30%. In one Nebraska example, a sheltered house used 23% less fuel; in South Dakota, a sheltered house used 34% less electricity. In southern Idaho, field crop yields rose 1 to 7% with windbreak protection. These are older studies, and results depend on the site, but the pattern is consistent.

The Nebraska guide notes other effects too: slightly higher humidity behind the trees, and livestock that use less feed when sheltered. One caution: sheltered areas can frost on calm, clear nights, because the trees also slow the air that would mix the cold away.

Hedgerows: shelter that feeds

A hedgerow is a living fence. NRCS defines it as dense perennial vegetation planted in a line. Hedgerows for wildlife include at least one row of woody plants, and pollinator hedgerows should provide abundant pollen and nectar, with plants blooming from early spring through late summer, protected from pesticide drift.

The Xerces Society's hedgerow guide suggests at least three flowering species for each bloom period: early, middle, and late. Since about 70% of North American native bees nest in the ground, it advises avoiding landscape fabric where possible. Space shrubs about 4 to 10 feet apart and wildflowers 2 to 3 feet, plant in fall when you can, mulch against weeds, and water about an inch a week for the first two years.

Make it edible

A windbreak can feed you too. NRCS standards encourage species that produce edible fruits and nuts, as long as the windbreak still does its job, and prohibit invasive species. In practice that can mean hazelnuts, serviceberries, elderberries, or nut trees in the rows, chosen to suit your zone, with conifers for winter protection and deciduous trees on the south and west sides of buildings for summer shade.