Written from our field experience coating homes across Lexington and the Bluegrass.
The Short Answer
Before you clean anything, figure out what you actually have. It changes everything.
Soft, smeary black or gray growth that wipes off is usually mold or mildew. That responds to a gentle wash with a mildicide, and then a durable coating to keep it from coming back.
Hard, tar-like raised dots that will not budge and leave a brown stain are a different problem entirely. That is artillery fungus from your mulch, and it has to be physically removed and controlled at the source. And whichever one you have, never blast vinyl with a pressure washer.
Here is how we tell the two apart on site, and what to do about each.
First, Identify What You Are Actually Looking At
This is the step almost everyone skips, and it is the one that matters most.
Homeowners call us saying they have “black mold” on the vinyl. A good number of the time, it is not mold at all. It is a fungus that comes from the landscaping, and it does not respond to any of the usual mold treatments.
We see it most on light-colored vinyl near mulch beds. Telling which problem you have takes about twenty seconds, and it saves you from scrubbing at something that was never going to wash off.
Mold and Mildew
Mold and mildew are biological growth that feeds on moisture and shade.
It usually looks like a soft film or fuzzy patches, gray to black, and it spreads over damp, shaded walls. The north side, spots under overhangs, and areas near dripping gutters are where it shows up first.
The tell is simple: it smears when you wipe it, and it responds to cleaning.
Artillery Fungus (Sphaerobolus stellatus)
Artillery fungus is the one that fools people. It is not mold, and no spray dissolves it.
It grows in hardwood mulch, then fires tiny sticky spore masses toward light, which is why they land on your siding. The spots look like specks of tar or splattered mud. They stick like superglue, and when you finally pry one off, it often leaves a brown stain behind.
A few things we have learned to look for:
- It favors light-colored and reflective surfaces, since the fungus shoots toward the brightest thing it can find
- The spots are hard and raised, not soft or smeary
- They cluster on the lower half of the wall, closest to the mulch
- They are nearly impossible to remove cleanly once cured
If this sounds like what you have, our mold and mildew page covers the biological side, but artillery fungus needs its own approach, below.
A 20-Second Test
Pick one spot and try to wipe it with a damp cloth.
If it smears or lifts, you are dealing with mold or mildew. Treat it as biological growth and wash it.
If it is stuck hard, feels like a little bump, and smears brown when you push at it, that is artillery fungus. Stop scrubbing and switch to the removal method for it, because washing will not work.
If It Is Mold or Mildew (safe removal)
Good news here: real mold and mildew on vinyl clean up without much drama.
The method we trust:
- Wet down the plants around the wall and cover what you can.
- Apply a mildicide or an oxygen bleach solution, working from the bottom up.
- Let it dwell so it kills the growth instead of just rinsing the surface.
- Agitate gently with a soft brush where needed.
- Rinse thoroughly with normal garden-hose pressure.
One rule we never break: do not force high pressure up into the seams and laps of the vinyl. Water driven behind the panels does not dry out, and that is how you trade a surface stain for interior mold.
If the mildew keeps returning every year, the wall is telling you the surface holds moisture. That is worth fixing at the surface, which we come back to below.
If It Is Artillery Fungus (a completely different job)
Here is the honest part most cleaning guides gloss over. Artillery fungus is stubborn, and there is no magic remover.
No fungicide is registered to treat it. No spray dissolves the cured shell. Anyone promising a chemical that melts it off is selling you something.
Removing the Spores
Timing is everything. The spore masses are far easier to deal with while they are fresh.
If you catch them within a day or two, sometimes a little vegetable oil and a plastic scraper will lift them. Once they harden, you are into physical removal only.
What actually works, done gently:
- A plastic scraper or a plastic putty knife to lift the dots
- Fine steel wool or a melamine sponge (magic eraser) used lightly for what remains
- A tarp laid under the work area, since the spores can stay alive for years and re-infest the mulch if they drop back in
Be honest with yourself about the outcome. Even careful removal can leave a faint brown stain in the vinyl. And skip the pressure washer. High pressure does not remove cured artillery fungus, but it will damage the vinyl and drive water behind it.
Stopping It at the Source (mulch control)
You will never win at the wall if you ignore the mulch. The fungus lives there, so that is where you stop it.
- Replace hardwood or wood-chip mulch near the foundation with pine bark nuggets or cedar, which are far less hospitable to it
- Keep mulch pulled back a bit from the siding and the foundation
- Keep the layer only two to three inches deep, and rake it now and then
- Refresh it with a fresh layer each year
Penn State Extension, which has done the deepest research on this fungus, also found that mixing well-finished mushroom compost into the mulch helps suppress it, because the compost introduces organisms that crowd the fungus out. Their full write-up is a solid read if you want the science.
How to Keep Black Spots From Returning (and what if the vinyl is stained for good)
This is where we split the two paths again, because the long-term answer is different for each.
If it was mold or mildew: the growth came back because the surface stays damp. A breathable, mildew-resistant ceramic coating changes that. It goes on far thicker than paint, blocks liquid water while letting vapor escape, and is built to resist mildew, so growth is much slower to return. To be straight: a wall in deep, permanent shade may still need an occasional rinse, but the yearly scrubbing mostly ends.
If it was artillery fungus: here is the honest limit. A coating will not stop spores from launching out of your mulch. That is a landscaping fix, full stop.
What a coating can do is restore the siding. If your vinyl is peppered with permanent stains or looks pocked and tired from years of this, we can prep and coat it for a clean, uniform finish instead of you living with the marks or replacing the whole wall.
If you want to understand how the coating works, here is what ceramic coating paint actually is, and here is how we approach coating vinyl siding specifically.
When to Call Rhino Shield of Cincinnati and Kentucky
If your vinyl is stained or chronically spotted and you are tired of fighting it, we are glad to take a look.
Our estimator, David, comes out personally, identifies exactly what you have (mildew, artillery fungus, or both), and tells you honestly what will help. Sometimes that is a good cleaning and a mulch change. Sometimes it is restoring and coating siding that is stained for good.
The assessment across Lexington and the Bluegrass is free. You can request a free quote or reach the Lexington team directly.
Rhino Shield of Cincinnati and Kentucky 222 Midland Ave #6109, Lexington, KY 40508 (859) 695-2718 Mon to Sat, 9:00 AM to 7:00 PM
FAQ
What are the tiny black spots on my vinyl siding?
If they are soft and smear when wiped, they are mold or mildew. If they are hard, tar-like, raised dots that stick firmly and leave a brown stain, they are artillery fungus, a mulch fungus that shoots sticky spores onto siding. The two need completely different fixes.
Is it black mold or artillery fungus?
Do the wipe test. Mold and mildew smear and respond to cleaning. Artillery fungus is stuck hard, smears brown when you push it, and clusters on the lower wall near mulch beds and on light-colored siding.
How do I remove black spots from vinyl siding?
Mold and mildew come off with a mildicide or oxygen bleach, applied gently and rinsed well. Artillery fungus has to be removed physically with a plastic scraper and a melamine sponge, ideally while fresh, and even then a faint stain may remain.
Why won’t the black spots wash off?
Because they are probably artillery fungus, not mold. The spore masses harden and bond like superglue, and no spray or fungicide dissolves them. Washing and pressure will not lift a cured spot, only careful physical removal will.
Does mulch cause black spots on siding?
Yes, in the case of artillery fungus. It lives in hardwood and wood-chip mulch near the foundation and fires its spores toward light-colored siding. Switching to pine bark nuggets or cedar and refreshing the mulch yearly is the real prevention.
Can black spots on siding be prevented?
Mold and mildew are prevented by keeping the wall dry and using a mildew-resistant surface. Artillery fungus is prevented at the mulch, not the wall, by replacing hardwood mulch, keeping it shallow, and mixing in mushroom compost. If the vinyl is already stained, it can be restored and coated.
