CORVALLIS, Ore. — During a rainier-than-usual winter and spring, moss eagerly invades lawns and settles in. The plush, low-growing plant draws strong reactions — many homeowners dislike seeing it overtake their turf.
That’s why Alec Kowalewski, Oregon State University's Grover Family Endowed Sustainable Urban Landscapes Specialist, fields so many questions about how to eliminate moss. But before offering solutions, he offers a reality check.
“People have the idea that if they put product down to control it then that’s the end of the story,” he said. “There’s a misconception that once moss is killed, it won’t come back. But it will if you don’t change the environment.”
Why moss thrives in lawns
Moss excels in conditions that stress turfgrass:
- Moist, shady sites
- Compacted soil
- Low nutrients
- Poor drainage
“Moss is like a lot of weeds,” Kowalewski said. “It will do well in tough situations and doesn’t need as many nutrients as lawn does.”
A thriving, dense lawn is the best long-term defense. To achieve that, two environmental factors must improve: shade and soil drainage.
“No matter how many different types of grasses you try, they won’t succeed in shady areas,” he said. “Trees and grass don’t do well together.”
Step 1: Remove or reduce shade
The only lasting solution for shade-related moss is to thin or remove trees. Once sunlight reaches the lawn, turfgrass can compete again.
Step 2: Remove moss and prepare soil
After improving light conditions, remove existing moss.
Options include:
- Renting a dethatcher and raking moss down to bare soil
- Raking by hand if moss pressure is low
Moss roots are shallow, so removal takes little effort.
If soil is compacted, use a core aerator — available at rental shops — to help air and water reach roots. Aeration is usually needed only in high-traffic areas.
“I’ve never aerated my perennial ryegrass lawn,” Kowalewski said.
After removal, replace mossy areas with sod or seed. Spring through Memorial Day is an ideal planting window, when weather warms and moss growth slows.
Fertilizing guidelines
A balanced approach to fertilizing supports healthy turf.
- Use an all-purpose lawn fertilizer rather than nitrogen alone.
- Apply 1 pound of actual nitrogen four to six times per year in spring and fall.
- Newer lawns require more fertilizer than established ones.
Low soil pH can also weaken turf. If pH drops near 5.0, nutrients become less available and aluminum toxicity increases — conditions moss tolerates but grass does not.
- Test soil before applying lime.
- If needed, apply 25 pounds of lime per 1,000 square feet in spring and again in fall.
- Re-test soil every three to five years.
Irrigation practices that support turfgrass
Surprisingly, irrigation is essential for managing moss because vigorous grass outcompetes it.
Current research recommends:
- Apply a total of 1 inch of water per week
- Water three to four times per week, applying 1/4 to 1/3 inch at each irrigation
- Increase to five times per week during extreme heat, but keep each application below 1/4 inch
Use a tuna can, rain gauge or plastic cup to measure output.
How mowing affects moss
Mowing correctly strengthens turf:
- Mow weekly.
- Remove no more than one-third of the grass height at a time.
- Mowing more often at lower removal rates encourages lateral growth, which shades out weeds and moss.
Products for moss control
If you choose to use a product, Kowalewski recommends sulfate-based options:
- Ferrous sulfate
- Iron sulfate
- Ammonium sulfate
These are environmentally friendly and work best when spot-applied as soon as moss appears. Because sulfur lowers pH, occasional lime applications may be needed — but only after soil testing.
Gardeners who opt for chemical herbicides should look for products containing:
- Soap of fatty acid, or
- Carfentrazone
Always read and follow label directions. Even with herbicides, moss will return unless underlying conditions improve.
Learn more
Consult these Oregon State University Extension publications for additional guidance:
Previously titled If you mind moss, get on board with preventative measures
