Correcting Mossy Lawns

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How to get rid of moss in the lawn is one of the frequently asked questions on our Ask An Expert question-and-answer service.

Soil and shade conditions that weaken turf grasses are ideal for moss growth.
Photo: Brian McDonald, OSU Extension Service

In the same way that fever is a symptom and not the disease itself, moss is an indicator of underlying problems. Lawn grasses need moist, fertile, well-drained and aerated soil, and at least a half day of sun to thrive. Most grasses grow best in soil with a pH between 6.0 and 7.5. When growing conditions fall outside of these boundaries, grass becomes weak and easily overtaken by competing plants, including moss.

Ridding a lawn of moss starts with an assessment of the growing conditions.

  • Check the sun and shade pattern. If trees and shrubs have grown large enough to cast daylong shade, they may need thinning to allow more light to reach the lawn. If the sun is blocked by buildings or trees that can’t be thinned, consider a shade-loving groundcover alternate.
  • Conduct a soil test. Collect soil samples from the lawn and test it yourself or send to a testing laboratory for nutrient and pH analysis. The test results will include recommendations for nutrients and pH correcting additives to apply. To find a testing lab, consult the Extension Service in your area.
  • Check the drainage. If water puddles and stands after rainfall, add a drainage outlet, if possible. If water drains too quickly and doesn’t retain moisture, gradually add organic matter, such as compost. Broadcast a half-inch of screened compost over the lawn in spring and fall each year to improve the soil texture.
  • Consider soil compaction. Heavy foot and machine traffic compresses the soil and drives out the tiny air pockets that roots need to grow. Poor drainage can be a symptom of soil compaction. Rent a core aerator once a year to loosen up the soil.
  • Select the correct grass seed. Use a high-quality mixture that matches your growing conditions and planned use. Look for named seed varieties on the label.
  • For more on lawn care:

    • OSU Extension Service research-based educational materials about lawns
    • University of California Guide to Healthy Lawns

    Ann Whitman, Horticulturist

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