How To Clean Moss Off Rocks

Coping Constructively With Mossy Madness

I always get a kick out of earnest magazine articles that explain how to create a mossy patina on clay pots. Evidently clean terracotta pots looks too obviously new and a mossy coat will give them an authentic, ancient English look. Well, the good news is that we Northwestern gardeners don't need to mess with buttermilk or buy packets of pulverized moss starter. All we have to do is wait, and not very long. Before you know it, your pots will be mossy, and probably your house will be too.

If not actually mossy, our houses (and pots, and deck furniture) often accumulate a thin coating of pollen and mold, which has that authentic old English look as well. One way to deal with this is to paint buidings and outdoor furniture that same color. Indeed, my house is painted with Benjamin Moore Nantucket Grey, with Sussex Green trim, both of which are a pretty good match for the pollen/mold blend in my region. I discovered this by taking a piece of pollen-crusted wood to the paint store and matching it to paint chips. So simple!

A Kitchen Moss Remover

Of course, paint just hides the problem (and I'm fine with that). I find the very best way to reduce moss and mold presence is with plain old baking soda. Years ago, I used a home-made baking soda spray with a sticking agent that was great for cleaning up mossy furniture, decking, walkways and so on. A few years ago I learned that all you really need to do is sprinkle plain baking soda around. I've since tried it and sure enough, it works beautifully and surprisingly fast.

For the past few years, I've kept my north-facing roof moss free by sprinkling it with baking soda each summer. Recently I treated a very mossy stone walkway with baking soda and despite the cool, damp weather, the moss was all dead in a week. Here's how it works: Sprinkle roofs, decks, furniture, and walkways generously with baking soda. Next, even out the coverage with a broom or brush. Let it stand for a few days, or until moss turns golden and starts to flake away. Scrub or scrape off moss and rinse away excess soda and you're done until next year. This is effective with getting rid of the mold/pollen buildup as well.

Safe and Simple

The best aspect of this totally simple treatment is that, unlike most commercial moss killers, baking soda won't harm garden plants, soil, or water. Dumping a whole bagful on a given plant won't be helpful, but runoff from a roof or deck cleaning job won't hurt anything.

I was also asked by a reader whether he could safely collect rainwater off his roof if he used a toxic moss killer to keep the roof clean. The answer is no. Rainwater contaminated with zinc, iron or copper should not be used on edible plants and why not switch to basic old baking soda?

The Non-Metallic Answer

Moss killers based on zinc or copper create toxic runoff that can harm fish and aquatic life (as well as people, in high enough concentrations). Iron solutions are less toxic (though not entirely harmless) but they can permanently stain roof shingles, decks, siding, and lawn furniture, as well as concrete walkways.

Is it possible to prevent moss from invading lawns and garden beds in the first place? Well, this is the moss capital of the world, but there are some things that will help. Most important are to improve the amount of light and air circulation in the garden and to change soil from fungal to bacterial domination. That last is best accomplished by adding compost annually to beds and lawns to balance soil acidity and open up compacted soils. Have a skilled arborist prune trees to allow more light and air to reach shady areas. Finally, don't over-plant tall shrubs and trees again!

Foliar Spray For Plants

Almost equally simple is this anti-fungicidal solution, which is effective against powdery mildew and molds on plant foliage. It's also safe to use on edible plants (just rinse well as usual before eating them), and on lawns with red thread or fairy mushroom rings. in addition, this baking soda solution helps prevent early blight on tomatoes, a common problem in the maritime Northwest.

Baking Soda Solution For Plant Problems

1 tablespoon baking soda (any kind)
2 tablespoons canola oil
1 gallon water
1/4 teaspoons mild castile liquid soap (Dr. Bronner's or similar)

Thoroughly wet down affected foliage/lawn, then apply this milder version, shaking the spray container frequently to keep solution from separating. Spray foliage top and bottom (if applicable) or saturate well (lawns). Repeat weekly or as needed.