Both water and wind can erode soils, carrying your valuable topsoil downstream or downwind. Water erosion happens most often on sloping ground that is bare and exposed to the elements. Erosion by wind occurs mainly in areas with high prevailing winds, such as on hilltops, over flat prairies, and along the ocean.
Water erodes soil in two ways: one is by the action of raindrops breaking the soil surface into tiny crumbs that are splashed and set in motion by the force of the raindrops. Although not seriously damaging in itself, this is the beginning of more serious erosion.
The other way water erodes soil is by its cutting and carrying power as it courses downhill. The more concentrated the water is, the faster and more damaging the erosion. This type of erosion can dig up slopes overnight and create huge gullies in days.
Because of the power of large amounts of water, it is difficult to stop erosion in steep gullies. About the only ways are to construct retaining walls to slow the flow of water, or fill the gully with large rocks or other objects too large to be moved by the water.
However, it’s relatively easy to stop erosion where the water hasn’t had an opportunity to build up force. It can be done by placing a protective cover over the soil or by shaping the land to eliminate the slope.
Protecting the Soil
The beginning of preventing erosion is to break the force of raindrops on bare soil by covering the soil with something. A mulch or a cover of plants works well for this. The next step is to slow down the water running over the surface. Mulches and ground covers do this job, too, as does erosion control netting.
Mulches are quick and easy to apply, inexpensive, and quite effective. Raindrops that hit a mulch are reduced to a gentle trickle when the reach the soil, and sink into the soil rather than running over its surface. However, most mulches must be reapplied at regular intervals. If erosion is a serious problem, such as on steep hillsides or regions that get torrential downpours, select a coarse or fibrous mulch, such as bark chunks, straw, or pine needles. Hold the mulch in place with erosion control netting on steep hillsides.
Ground covers take longer to establish than a mulch, but are longer lasting. Lawns make ideal ground covers to prevent erosion. Their closely-spaced blades keeps water from picking up enough speed to cut into the soil no matter how steep the slope. Ground covers that root where branches touch the ground, or that spread from runners or roots, eventually form dense mats that effectively prevent erosion.
Erosion Control Netting is designed to keep water from picking up speed as it flows down a slope. Because of their open spaces, these nettings don’t protect the soil from raindrop erosion. Because they can be pegged to even the steepest slopes, they can be used in almost any situation. Erosion control netting may be made of jute or polyethylene. Both degrade, but under different situations. Jute rots when it is damp, and will disappear after 2 or 3 years in all but the driest areas. Polyethylene degrades when exposed to sunlight. It will also disappear in a few years, but only if exposed to sunlight. Buried in the soil or under a mulch, it can persist for years.
Netting is pegged in place with wooden pegs made for the purpose, which also rot in a few years.
An erosion control project might make use of any or all three of these methods. For example, you might hold a steep bank in place with jute netting spread over a couple of inches of straw mulch, and plant a ground cover in the holes of the netting. By the time the netting rots, the ground cover will be established.
Breaking the Slope
Another way to handle erosion is by shaping the land into terraces. This is a time-consuming and expensive solution, but allows land to be used for gardening that might otherwise not be available. Low retaining walls—those under 2 or 3 feet high—are simple to build. Higher walls bear much more weight and should be designed by an engineer. To keep your job simple, design it with more, but lower, walls.
Although a serious region-wide problem in some areas, few gardens outside of these areas are bothered by wind erosion. Probably the most common troublesome situations are seaside and hilltop gardens. Soil can be protected from wind erosion by two of the same three methods used to protect the soil from water erosion: mulch and a plant cover. Select a mulch with particles heavy enough to stay in place in the wind. Almost any ground cover will keep soil from being shifted by wind, but not all ground covers will thrive in windy locations. Ask at your local nursery for ground covers suited to your area.