A bare hillside allows for erosion that can lead to muddy messes or even landslides; not to mention, the barren landscape isn't exactly pleasing to look at. While there is no one easy answer to the problem of hillside erosion, you have options for solving the problem. The method you choose will depend on how the hillside fits into your landscape, and the amount you want to budget for the project. No matter how you address hillside erosion, select a solution that will also add beauty to the landscape.
The first thing many people think of to help remedy an eroding hillside is a retaining wall. These can be made of wood, railroad ties, concrete blocks or natural stone. They are built at the base of the slope and help stabilize the soil, preventing it from washing downhill. You can reduce the angle of the slope by creating a vertical structure that the soil can pile up behind. This also provides a space to plant. It is one of the most expensive approaches, but is usually necessary for extremely steep slopes. You may attempt to build smaller retaining walls yourself, but more than likely you will want to hire a contractor. Walls over 3 feet tall require permits and special engineering considerations, so professional help is required in those situations.
The general theory of erosion control is to slow the flow of water as it runs down a hillside, so that it soaks into the soil rather than gaining momentum and carrying with it the soil in a snowball effect. Terracing a hillside makes flat, walkable areas where you can amend the soil and plant as you wish. You may be familiar with the concept of terraces. They are seen in Asian paddy farming, terraced farming in South America, old vineyards in southern Europe, in addition to home landscapes in the United States. Terracing can be applied to solve your erosion problems and create a stunningly beautiful planting area in your yard. Terracing is a lot of work to do my hand, so look for a licensed contractor who can do the work for you with machinery. On steeper slopes, terracing will definitely require retaining walls, though gentle slopes can be terraced using grass or other vegetation to hold the soil in place. Once the terraces are in place, you can plant your flowers, herbs, vegetables or other plants.
Erosion problems are characterized by a lack of vegetation -- the loss of soil leads directly to a loss of vegetation. One solution is to make planting shelves, or miniature terraces, throughout the hillside -- if it is not too steep to safely navigate. To make a shelf, stand above the place where you want to plant, and dig down into the hill about 6 to 12 inches, making a little mound of soil on the side of the slope. Then, stand below the planting location, and use a hard metal rake to flatten out the excavated soil into an area big enough to plant on -- about 1 foot deep into the hillside and one or 2 feet across the width of the slope is sufficient for anything but a large tree. Plant tough species that don't need fertile soil conditions or a lot of water.
Add compost to the planting hole or spread on the surface of your dirt shelves. Cover planting shelves and the rest of the slope with a 4 to 6-inch layer of mulch. Pine straw, wheat straw and finely shredded bark cling better to soil. Remember to always wear gloves when working with soil to protect from any harmful pathogens that may be present.
Erosion Control Fabric
Another approach to re-establishing vegetation on an eroded hillside involves the use of geo-textile mats, also known as erosion control fabric. The many varieties of these materials allow water to percolate and plants to grow through them, while preventing soil from being washed downhill. Some are specifically designed to help establish grass on slopes. The soil must be prepared in advance, and then seeded and covered with the fabric. The seeds germinate and the plants grow through the spaces in the material. Similar fabrics can be used on slopes around perennial plants, shrubs and trees -- plant the larger specimens first and install the fabric to cover the slope all around them. Then cut holes into the fabric for the small plants, and plant them directly into the soil under the mat.