The short answer
The tiny black dots peppering your siding are spore masses from artillery fungus (Sphaerobolus stellatus), an organism that lives in wood-chip mulch and fires its spores up to 20 feet toward light-colored surfaces. They bond like adhesive and cannot be pressure-washed off once cured — realistic removal only happens within weeks of the outbreak, and lasting prevention means changing the mulch.
What's Actually Shooting at Your House
Artillery fungus — nicknamed shotgun fungus — is a tiny organism that colonizes rotting wood-chip mulch. When its fruiting bodies mature, they build internal pressure and literally fire their spore packets (called peridioles) at the brightest surface they can sense, up to 20 feet away. That targeting is why the specks concentrate on white and light-colored siding, gutters, downspouts, car finishes, and window frames — and why the pattern always faces a mulch bed. Each speck is about the size of a pinhead, tar-black, and stuck astonishingly hard.
Why They Won't Wash Off
The spore mass cures onto the surface with a natural adhesive that Penn State plant pathologists — who've studied this organism more than anyone — compare to super glue. Once cured, the bond is stronger than the surface's tolerance for removal: pressure high enough to blast the specks off vinyl or aluminum is pressure high enough to damage the siding, and even then the dot often shears off while a brown stain stays behind. There is a removal window, but it's short — within the first few weeks of an outbreak, while the masses are fresh, careful work with soft-wash chemistry, warm water, and patient agitation can lift a real share of them. After a season of sun-curing, honest companies stop promising.
What Realistic Removal Looks Like
Our approach starts with an age assessment: fresh outbreaks get treated promptly and thoroughly, because the clock matters more than the chemistry. Older specks get honesty — we can usually improve the appearance by cleaning the wall around them and reducing the specks' visual weight, and gentle mechanical removal spot by spot is possible on some surfaces, but a wall carrying years of cured artillery fungus is often looking at a repaint-or-replace conversation for the affected sections, not a wash. We'd rather tell you that during the walkaround than after an invoice. What we never do is blast at them — that trades a speck problem for a siding problem and solves neither.
The Fix Is in the Flower Bed
There is no spray that kills artillery fungus in mulch — Penn State's program tested 27 mulch types and found the only real lever is what the beds are made of. Wood-chip and shredded hardwood mulch against a light-colored wall is the high-risk combination. Lower-risk choices include large bark nuggets, cypress, and blends containing spent mushroom compost, all of which supported dramatically less fungus in testing; stone, rubber, and pine straw take the fuel away entirely. If you keep wood mulch, keep it away from the house on the sunny-splash sides, refresh it annually so the surface layer stays fresh, and rake it periodically — the fungus thrives in moist, aged, undisturbed chips.
The Bottom Line
Artillery fungus is one of the few exterior stains where the honest professional answer is 'it depends how old it is.' Fresh: call quickly and much of it can go. Cured: manage expectations, clean the wall, fix the mulch so the barrage stops. Either way, the house wash that handles the rest of the wall is the right first step — and if you're seeing your first specks now, this is the week to act, not October.
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