Robert F. Brzuszek is an assistant professor of landscape architecture at Mississippi State University.

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Landscape Solutions
by Bob Brzuszek       #Landscaping   #Slopes

There always seems to be a catch to that perfect piece of property. The views of the rolling countryside may be breathtaking, the sparkling clear creek at the back of the property might be picturesque — but, unfortunately, part of the property is so steep that it requires rappelling gear just to mow the lawn. What does a gardener do when there is an area that is “un-doable?”

 

STEEP SLOPE SOLUTIONS


This waterfall placement takes advantage of a steep slope and is an elegant solution to solving drainage problems.

First, it depends on the severity of the slope. Steep slopes are defined as areas of land that rise greater than 20 percent in angle. That’s 2 feet of elevation change in 10 feet of walking. In other words, if you are winded by the time you walk to the top of the hill — that’s a steep slope. Depending upon the soil type, slopes that are less than 20 percent are usually more stable and easier to maintain.

Steep slopes can cause some major problems in the landscape. In addition to being incredibly difficult to mow, they often cause one of the greatest real estate losses by the erosion of topsoil. Sand grain by sand grain, the wonderful garden soil that was once at the top of the hill is now lying at the bottom. Gravity happens. Erosion problems can become so severe in some areas that large gullies can form, which is exactly how the Grand Canyon was born. These gullies can continue to spread in size with each major rainfall as torrents of water wash through the gulch. If unchecked, severe erosion problems have been known to undermine the foundations of houses. So, it is best to take care of these severely eroded areas as soon as possible. Water naturally follows the lowest and easiest course, so it is best to retain or even create permanent drainage channels on a steep slope. Large permanent structures, such as boulders and stones or even constructed check dams, can be placed into gullies to prevent further erosion.

Nature’s solution: Planting the slope. Nature solves erosion problems with vegetation in even the steepest mountainous terrains. Trees and shrubs form a tight network of roots and stems that not only bind the soil particles together but also act to slow the force of rushing water down a hillside. Turfgrass on steep slopes can help to bind the soil with a network of roots but does not perform a very good job of slowing water runoff. Heavy rains can wash away turfgrass, root and all. Taller growing grasses, wildflowers, shrubs and trees do a much better job of slowing runoff. In the world of erosion, bigger is always better.

 

SUNNY SLOPES

If you ever wanted a wildflower garden, converting a steep, sloping lawn area to an open, sunny meadow is a good solution. Apply an herbicide to the existing turfgrass or other undesirable vegetation. The next step is to lightly till the soil to provide a loose seed bed. Drought tolerant wildflower mixes are readily available in large quantities from seed companies and should be lightly sown. It is a good idea to stabilize the soil until the wildflowers are up and growing. This can be done by spreading a light layer of fresh hay on the slope (the hay particles bind together and break the force of raindrops) or by securing an open plastic netting across the slope. The wildflowers can grow through the netting, and it will eventually decompose. Once established, the sunny flowering perennials and re-seeding annuals will secure the slope for years to come. Other drought and sun tolerant plants useful for slope stabilization include prostrate junipers, ivies, Rugosa roses and sedums. Use an erosion fabric and mulches that bind (such as pine needles) to prevent weeds from occurring on planted slopes.

 

SHADY SLOPES


Shrubs and trees help to stabilize loose soils.
 

Terracing is a time-honored and beautiful solution for a difficult slope.

Even with the fibrous roots of shade trees, erosive areas can still form on woodland slopes. Shade tolerant shrubs could certainly be used, but ground covers can create a more compelling woodland image. Low-growing vines, ferns and other perennials that carpet the earth will allow more of the woody trunks and stems to be appreciated. Partridgeberry vine, wood fern, mayapple, trillium, Jack-in-the-pulpit, woodland phlox and Indian pink are just a few of the shady perennial possibilities that will not only provide great beauty but can also help to stabilize soil. Even a thick carpet of fallen leaves acts just like a sponge and absorbs rainwater before erosion can occur.

Human solution: Changing the slope. Our agricultural forefathers knew a thing or two about farming a steep hillside. To make it productive (and through much effort), they would terrace the slope. Terraces reduce erosion by breaking a long hillside slope into shorter, more even steps. It provides for permanent architectural interest and creates more usable opportunities for gardens.

Many materials may be used for creating terraces. Treated wood, brick, rocks, concrete blocks and other masonry materials can be used to form walls. They can vary considerably in cost, durability and effort of construction — depending upon the materials used and the size of the area to be terraced. Masonry and stone cost considerably more than wood materials but more than make up for it in longevity.

Terraces are created by using a cut and fill method. Soil is removed to create a flat area, and this soil is used to fill a low area. It is recommended that do-it-yourselfers limit their wall heights to just 1 or 2 feet high, as there is a tremendous pressure of water and soil behind a wall. It takes equipment, expertise and proper drainage to successfully construct retaining walls, and a landscape architect should always be consulted for proper materials and methods. Always check with local ordinances and building codes when considering a retaining wall or terrace.

Steep slopes can present challenges and creative opportunities in the home landscape. Whether you use nature’s solutions or human’s solutions, thoughtful planning and execution can result in an attractive and workable landscape for a difficult area.

 

(From State-by-State Gardening May 2005. Photos by Peter Gallagher.)

 

Posted: 04/11/12   RSS | Print

 

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