Help my moss is turning black!

Dear David,

I have had an outdoor waterfall and pond for about 10 years.  The moss is beautiful, growing on the majority of rocks closest to the waterfall.  Each year it seems to increase, with no special care from me, except for pulling any stray water plant growth.   This year it has slowly been turning black, from the bottom up, and some has died altogether.  I haven’t done anything different from the previous years.  No chemicals have been applied, etc.

Do you have any idea what could be causing it to die, and what if anything I can do.  I did remove a lot of it today.  Thanks so much.  Mary

Hello Mary,  It’s difficult to diagnose with so little information and so many parameters. It’s possible that black slime mold is affecting the area if it is wet all the time and if water plants are creeping up the moss they could easily help to spread this type of problem.  Removing the affected moss is a good precaution, monitor it carefully and ensure the water quality isn’t the problem.
If you need further assistance, really good close up photos of the problem will be needed for further diagnosis.

Best regards,

David Spain
Moss and Stone Gardens

Dear David, Thanks so much for your reply. I have looked at it and taken some pictures. It looks like whatever it is, it is totally “consuming” it. First it turns black and then it just disappears, with a black thin layer of slimey stuff. Is that what black slime mold looks like? And, is there anything I can do. I read about that problem in aquariums, but not in outdoor ponds. Thanks. mary

Hey Mary, the photos certainly do help with the diagnosis. It appears as though you have not only black slime mold affecting your moss but judging from the photos, grey mold as well. Molds are one of the few enemies of mosses and often occur in closed terrariums. Molds are partial to the same conditions that many mosses are. Constant moisture and shade can be a recipe for the slimy and fuzzy stuff to invade. The molds are however temperature dependent and you will likely not find them growing in cooler seasons. I have found that once the thermometer reaches 75 degrees Fahrenheit or above, and the moisture is constant, you should keep an eye out for the attack of the molds. Most of these attacks are easily remedied by removing the moisture, but if the problem is at the edge of your artificial water system, then removing moisture is tricky. You have already taken a good step by removing the moss that is affected. Trimming or thinning mosses that are growing into the water can also be a preventative. Mosses may reach for and grow into the water but that doesn’t mean that it’s good for them. Our artificial water gardens have a constant water level that natural streams or ponds do not, this consistent water line is not as forgiving as the rising and falling water lines of a natural body of water. When mosses have direct contact with a body of water, they wick the water into the moss mat. This can help feed the mosses growth but in certain situations can also lead to problems. One of these problems can actually be to drain the water system quicker than evaporation does alone, another is soggy soils and slime molds. Eventually these problems will find an equilibrium and take care of themselves, but the results may not be the desired lush moss growth right to the waters edge you envisioned. A little moss maintenance and trimming will help in this case to stop the wicking and soothe the soul.

Best of luck,

David Spain, a.k.a Moss Rock


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4 thoughts on “Help my moss is turning black!

  1. Robin

    Hi David,
    I am responding to the letter on black slime. I am FAR from any kind of expert but I had an idea. I didn’t notice where she was from but I know here in Florida if we have a problem in the garden that we hadn’t had for years and it just seem to show up we have to remember to “look up”. I noticed you told her that constant moisture and shade can help cause the slime, well most of the time here we forget how fast the tree limbs grow and start blocking the sun. It is gradual to us so we don’t notice it. I’m not saying that is the solution but it is another avenue she could explore.
    Blessings, Robin


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