Filter Strip

What it is:

A strip of dense herbaceous vegetation such as grass, trees or shrubs that filters runoff and removes contaminants before they reach water bodies or water sources, such as wells. Filter strips are most effective when used in combination with other agronomic or structural conservation practices.

How it helps:

  • The vegetation slows water flow and allow contaminants like sediment, chemicals and nutrients to collect in grass, trees and shrubs.
  • Filter strips improve water quality for fish and other aquatic life.
  • Grass, trees and shrubs provide cover for small birds, animals and pollinators.
  • Ground cover reduces soil erosion.
  • The vegetative strips move row crop operations further from a stream.

Planning ahead:

Filter strips are often the only break in the monotony of intensively-cropped areas. Increasing the width of the filter strip beyond the minimum required will increase the potential for capturing more contaminants in runoff and increasing carbon sequestration.

Consider the following:

  • Are adequate soil conservation measures installed above the filter strip?
  • Are plants adapted to your soil type?
  • Have you selected the correct plant species for the control you need?
  • Consider including species beneficial for pollinators and butterflies such as milkweed.

Design and Maintenance Criteria:

Filter strips are most effective on slopes of 5% or less and must be at least 15 feet wide on cropland and 50 feet wide on forestland. Steeper slopes require wider strips.

% Slope Minimum Width
0-10 15 Feet
10-20 20 Feet
20-30 25 Feet
  • Do not use a filter strip as a roadway.
  • Filter strips will be less effective under snow or during frozen conditions.
  • Avoid drift when applying herbicides on surround cropland.
  • Controlled grazing may be allowed if filter strips are dry and firm.
  • Repair rills and small channels that may have developed.
  • Control grazing if livestock have access to filter strips.
  • Mow (and harvest if possible) grasses several times per year to encourage dense vegetative growth. For ground nesting wildlife, avoid mowing during nesting periods.
  • Restoration may be needed if sediment accumulates.