When Moss Goes Bad
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Weed-Aside™ Herbicidal Soap
Q. I had a truckload of topsoil brought in to fill my raised beds. The beds are now covered with moss, as are some places where the topsoil wasn't used. These areas get sun six to ten hours a day. How do I discourage the moss?
- ---Linda in Troy
in Newark, DE
- ---Marilyn in West Alexandria, Ohio
So, the first thing to do is to take an honest look at the sunlight and airflow those beds are receiving. If you are incapable of taking an honest look, ask somebody else. Oh wait—I'll do it for you. It's dark as Hades in there! See what you can do to increase the sunlight and airflow: Cut back or remove brush and weedy growth just outside the area and thin out overhanging or air-blocking tree limbs—preferably over winter (the best and safest time to prune trees).
All of your plants (except the moss) will benefit. You'll be amazed at how dramatic the response can be when you trim back and/or remove a few plants from a crowded space.
Also test the soil. Most mosses thrive in an acidic environment and sometimes adding a little wood ash or lime to raise a highly acidic soil closer to neutral can make problems like this go away. And most plants would appreciate a friendlier soil too. Just don't use wood ash or lime near plants that need acidic soil, like azaleas, rhododendrons and blueberries. (Here's a previous Question of the Week about using wood ash to raise soil pH.)
And be sure to let the area dry out completely between watering. Shady spots don't generally need much supplemental water, and only your moss will be unhappy if you stop making it soggy in there. Here's a very important previous Question of the Week about watering wisely.
Q. Conditions have been just right for moss to grow on the shady side of our roof. Is there anything that can be done to kill the moss and prevent it from ruining the roof?
- ---Linda in Angelica
Q. We have moss growing between the cracks in our brick patio. Is there anything that can be applied to kill it off? Or do I just scrape it out?
- ---Thomas in Annandale, VA
Q. The brick walk around my garden gets very little sun and is covered in moss, which makes it slippery. I've seen suggestions on the web for spraying it with Clorox or sprinkling it with baking soda; and I also purchased some insecticidal soap.
- ---Sylvia in Philadelphia
And, as we've been saying, increase sunlight to the area and spread some wood ash. You might also want to scrub those bricks really clean and then apply friction tape, which has a sandpaper-like consistency to its non-sticky side. I use it to keep the slipperiness factor down on the wood decking we have under some trees. It works great, and is available in rolls (like masking tape) at most hardware stores and home centers.