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Plantings on Slopes

Scope

Plant sloped ground to reduce erosion.

  • Plant vegetation on any ground that slopes greater than 25%.
  • For any slopes greater than 50% (1 foot vertical rise for every 2 feet horizontal run) install plants that do not require mowing.
  • Consider terracing for steep slopes.

See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

 

 

Description

Installing plantings such as ground covers on steep slopes without sprinkler irrigation provides stabilization to prevent erosion and increase filtration as water passes down the slope.

Steep slopes in landscapes provide a challenge for the landscape design because of the potential for erosion and runoff from stormwater and irrigation water. Erosion can be a serious problem if vegetation is not established. Care should be taken to ensure that appropriate plantings are used and that only irrigation methods suitable for slopes are applied. South-facing slopes can warm up and dry out quicker than other areas, while north-facing slopes can be cooler than surrounding areas.

Considerations must be given to the plantings installed on slopes, as it may not be safe to operate a lawn mower on slopes greater than 2:1 (2 feet of horizontal run per 1 foot vertical rise). Trees and shrubs create a tight network of roots and stems that not only bind soil particles together, but also act to slow the force of rushing water down the hillside. Turfgrass on steep slopes can help to bind the soil with roots, but might not slow down stormwater runoff. Thus, heavy rains can wash away turf, roots and all. Taller growing grasses, wildflowers, shrubs, and trees do a much better job of slowing stormwater runoff from steep slopes.

Terracing is an alternative approach to planting on slopes. Open terraces can be dug into the slope in the shapes of steps. The existing slope can be cut, and the excavated soil can be used as fill. A low soil berm (ridge) can be formed at the front edge of each step or terrace to slow the flow of water.

The inspector will use a laser level, clinometer, or other method to determine if slopes are greater than 25 percent or 14 degrees (i.e., 4:1 slope), then verify that slopes greater than 25 percent have vegetated plantings (e.g., groundcover, shrubs, tall grasses, etc.).

Properly water landscapes on slopes.
Figure 1. Determine the angle of ground slope and plant ground cover accordingly (courtesy of U.S. EPA WaterSense Program)

 

Ensuring Success

The inspector will use a laser level, clinometer, or other method to determine if slopes are greater than 25 percent or 14 degrees (i.e., 4:1 slope), then verify that slopes greater than 25 percent have vegetated plantings (e.g., groundcover, shrubs, tall grasses, etc.).

Climate

Use climate-appropriate vegetation.

Training

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Compliance

The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

Environmental Protection Agency (EPA) WaterSense® New Home Specification

The EPA WaterSense New Home Specification states that:

Slopes in excess of 4 feet of horizontal run per 1 foot vertical rise (4:1) shall be vegetated.

This Retrofit tab provides information that helps installers apply this “new home” guide to improvement projects for existing homes. This tab is organized with headings that mirror the new home tabs, such as “Scope,” “Description,” “Success,” etc. If there is no retrofit-specific information for a section, that heading is not included.

Guidance for the measures described in this guide is applicable to both new and existing homes. Homes with established landscapes may require replacing turf and other plants to follow the guidance.

Properly water landscapes on slopes.
Figure 2. Determine the angle of ground slope and plant ground cover accordingly (courtesy of U.S. EPA WaterSense Program)

 

More Info.

Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

Case Studies

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Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Last Updated: 06/26/2017