Moss Getting You Down?

Beauty or Beast?
As residents of the Pacific Northwest, we’re no strangers to this group of small, furry plants that grow in our lawns and on our roofs, decks and sidewalks. Our damp climate, naturally acidic soils and ample shade provide ideal places for moss to grow green and lush. Unfortunately, our human attempts to eradicate this unwelcome visitor are usually without much long-term success.

Why Fight It?
The presence of moss in a lawn usually indicates that conditions are not optimal for grass to grow well. Why not re-evaluate our lawns and consider allowing moss to grow? Instead of spending lots of time and money removing moss or spraying it with hazardous chemicals, consider letting it grow in the bare spots between sun-loving lawn grasses, which seldom do well in shady, damp yards.

Why Keep It?
Moss is much lower maintenance than yard grass. The native ground cover never needs to be mowed or watered and doesn’t need any fertilizers or pesticides to grow green. Not only is using less lawnmower fuel, fertilizer and pesticide great for your pocket book, it’s also great for the environment! Chemical-free lawn care helps protect aquatic wildlife in our streams and rivers and children and pets in our yards.

*It’s important to note that moss can be a real hazard to roofs and other structures and should be removed. If you have moss on your home, or decide that you really need to get rid of the moss in your lawn, follow these environmentally friendly steps to manage your moss community.

Maintenance for Mossy Lawns

Step 1: Rake it – First, remove moss using a stiff metal rake or de-thatching rake.

Step 2: Add Competition - Re-seed scraped mossy areas with regionally appropriate shade-tolerant grasses. Apply about 25% of the sowing recommendation for a new lawn when overseeding only.

Step 3: Add Sun – Strategically, but sparingly, prune trees and shrubs to increase sunlight in the mossy area.

Step 3: Dry it Out – Aerate and de-thatch your lawn to keep air moving and moisture at a minimum.

Step 4: Don’t Over-Fertilize/Check pH – Fertilize your lawn only once per year in spring or fall. Use compost spread ¼ to ½ inches deep or a slow-release fertilizer. Extra fertilizer isn’t used by grass, but still encourages weeds and moss. If your soil is acidic, add ground limestone or dolomite lime, 6.0-7.0 pH is optimal for lawn.

Step 5: Mow Less – Frequent mowing stresses grass, making it less able to compete with moss. Wait to mow until your lawn is 3” to 4” tall to keep it strong and healthy.

Step 6: Water Less –Watering only 1 in/week (including rain) or letting your lawn go dormant during the summer will stress moss, while your grass will bounce back green and healthy with the fall rains.

Step 7: Consider Your Options – If your moss problem still persists, consider replacing the problem area with a flower bed or native ground-cover such as Fragaria vesca (woodland strawberry), Oxalis oregana (redwood sorrel) or Maianhemum dilatatum (false lily of the valley).


Mossy Roofs, Sidewalks, Decks and Patios

Step 1: Scrape it – Remove moss using a shovel, rake or stiff-bristled wet broom.

Step 2: Add Sun – Strategically, and sparingly, prune trees and shrubs to maximize sunlight in the mossy area.

Step 3: Keep it Clean and Dry – Regularly remove leaves and other debris to help keep moisture down.

Step 4: Avoid Zinc –Zinc strips and pesticide products are common for moss control, but are highly water soluble and highly toxic to our local fish and other aquatic wildlife.


Natural Alternatives to Chemical Moss-Killers
It might take a while for moss to get the hint and quit re-colonizing its old haunts. During this process, you can use an organic moss-killing spray to spot treat new colonies, but please use it wisely and follow the instructions. Organic sprays are typically oils, fatty acids, or iron sulfate that are very effective at drying moss out. Instead of killing grass out-right like some chemical moss killers, organic sprays cause surrounding grass to yellow but grow back green in 10-14 days. These products can cause skin and eye irritation and are toxic to aquatic wildlife, so use caution.

Local Suppliers of Natural Products
Concern Fast-Acting Weed Killer Safer’s Moss and Algae Killer
Flat Creek Garden Center

Worry-Free Moss and Algae Control
30039 SE Orient Drive, Gresham

Bonide Moss Max
503.663.4101
Portland Nursery
9000 SE Division St,
Portland 503.788.9000

For more information, contact Keri Handaly (City of Gresham Watershed Steward) at 503.618.2657, keri.handaly@ci.gresham.or.us or Jamie Stamberger (Water Quality Improvement Coordinator) at 503.618.2793, Jamie.stamberger@ci.gresham.or.us.

* Please remember that all moss-killers may be harmful to aquatic wildlife such as fish, frogs and salamanders and should be avoided if at all possible because our roof and street drains lead directly to our local streams without treatment.