How Do Perennials Help With Soil Erosion?

What Is Erosion?

• Erosion is the gradual or rapid wearing away of soils due to abrasive action by wind and water. Bare soil is most susceptible to erosion simply because it has nothing to hold it in place. Compacted soils as well as hard surfaces like pavement and house roofs contribute to erosion by allowing water to flow freely over their surfaces, carrying with it particles of dirt that accumulate elsewhere, usually in low areas such as streams, lakes, bays and estuaries.

Types of Erosion

• Wind and water are the two primary means of soil degradation. Turbulent gusts of wind close to the ground kick up dust and dirt particles, which either blow away or dislodge even more dirt when they collide again with the ground. This is especially problematic in plains areas, where wind builds strength by traveling across vast distances, unchecked by obstacles such as trees or geography. Erosion by water is more common, created by excess precipitation or other water carried across hard-packed or already waterlogged soil. Water erosion causes rutting, best demonstrated by a deep, starkly etched stream bank lined by trees with exposed roots.

How Plants Help

• Because of persistent roots that survive from year to year underground, virtually any perennial will benefit an area affected by erosion. Roots help keep soil lodged firmly in place, while the stems and leaves prevent raindrops and other precipitation from directly hitting the ground. Trees and shrubs provide protection from wind. Even in the winter, when most perennials are dormant, allowing dead plant matter to remain on the ground helps reduce erosion, again functioning as a barricade against rainwater striking bare earth.

Impacts of Erosion

• Water that runs over exposed soil is effectively lost groundwater, since underground sources are replenished by water that percolates through the ground. Flowing water also washes away valuable topsoil, which leads to wasteful fertilizer use in an attempt to increase fertility. Excess fertilizer runs off into bodies of water, creating so-called “dead zones” from too much algae that blooms in the presence of a glut of fertilizer nutrients. Pesticides and other chemicals, washed downstream by runoff from eroded soils, accumulate in sediments as well as in the bodies of aquatic animals and are eventually passed up the food chain as these animals are eaten. On unprotected hillsides, gravity and water action causes the ground to sag and creep downward, leading to unstable soils and landslides.

Planting Suggestions

• Perennials with tough, fibrous root systems, such as ornamental grasses, are particularly good choices to help reduce erosion, because the roots keep the soil from moving. Ground covers and vines help reduce erosion by providing surface cover from wind and rain, while compact, shrubby perennials combined with grasses help reduce wind erosion by interrupting blasts of air. Plants native to the local area are almost always the best choice for erosion reduction and control, because they typically establish faster, are tolerant of harsher environmental conditions and require little in the way of special care or feeding.