Control moss by keeping grass healthy

Maintain healthy grass to keep moss from invading.

Many homeowners struggle with moss that invades lawns as winter rains provide just the right conditions for its growth.

“The most frequent winter time question I receive regarding lawn maintenance is, ‘How do I get rid of moss?’” said Alec Kowalewski, turf grass specialist for Oregon State University Extension Service.

To answer that question, Kowalewski and Brooke Edmunds, a horticulturist with Extension, developed a publication and video on Managing Moss in the Landscape in Western Oregon. The new resources dive into the three steps to rid your lawn of moss, a frustrating process since it first involves dealing with the conditions that encourage moss.

“Some people want the quick fix,” said Edmunds. “They don’t want to think that it might be too difficult to have lawn in the shade. But grass doesn’t grow well in wet, shady areas and won’t outcompete moss.”

Moss is like a lot of weeds, Kowalewski added. It will do well in tough situations and doesn’t need as much nutrients as lawn does.

Don’t just put a Band-Aid on it with chemicals, Edmunds said. Instead keep the lawn healthy by reducing shade and moisture and following good cultural practices. That includes keeping pH between 6.0 and 6.5 by adding lime if necessary. Fertilize twice in spring and twice in fall. Mow and irrigate appropriately.

To maintain a healthy lawn, Edmunds recommends pruning trees to let in more sunlight and dealing with excessive water with French drains or tiles.

If that doesn’t bring the desired results, Edmunds recommends treating the moss with appropriate chemicals. Another option is to dethatch the lawn with a rake or rented dethatcher to pull up the moss and then reseed bare spots. If all else fails, you’ll need to do a full renovation.

If you choose to use a product to control moss, there are several available. Kowalewski recommends sulfate products such as ferrous sulfate, iron sulfate and ammonium sulfate. These are environmentally friendly options, he said. Apply by spot treating as soon as moss appears.

Sulfur products such as these will lower the soil pH, making conditions acidic. An occasional application of lime, which will raise the pH, is recommended when you are making frequent sulfur applications. Before applying lime, test soil pH with a gauge available at garden centers and home improvement stores.

If you decide to use a chemical herbicide, Kowalewski recommended that gardeners choose products with soap of fatty acid or carfentrazone as an active ingredient. Read labels and follow all safety precautions when using pesticides. Remember, though, even using herbicides to kill moss won’t keep it from returning.

When using herbicides, be sure to use protective gear and to follow all of the label’s recommendations.

Some people like moss. For them, Edmunds said, “If you’re OK with it, carry on.”

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