Question: “Have you heard of Condy’s Crystals as a fungicide?”, asks T.W., a school head gardener in Brisbane.

Potassium permanganate was created 1659 by Johann Glauber. To make it, he combined manganese oxide ore with potassium hydroxide forming the compound KMnO4. At school I was taught this is a reducing agent, meaning potassium permanganate loses electrons and is oxidised in a chemical reaction that can be used to kill certain fungi.

A solution of potassium permanganate crystals, dissolved in water, has been harnessed as a disinfectant and fungicide in medicine, vigorously promoted and commercialised in the 1800’s by Henry Condy leading to its branding in the USA as Condy’s Crystals.

In medicine, it has been used to treat fungal infections of the skin like eczema and athlete’s foot.

It was widely used in the British army and this use by my paternal grandfather, a British WW 1 sergeant major ensured my father had been drilled to always have some to hand in the medical cabinet. As a teenager, I bought potassium permanganate over the counter at White’s Chemist in SE London. Dad used a solution of it liberally to control athlete’s foot which we all caught regularly by visiting local swimming pools. 

At the line up at the local swimming pool my toes, stained Mission Brown (a name that resonates with Australians born last century) stood out. Potassium permanganate works excellently well, but the stain was a source of acute poolside embarrassment. It lasts until the skin is naturally sloughed off.

Potassium permanganate stains everything it touches, so in the 1960’s our family had a foot bath reserved exclusively for it stored under the stairs near the medical cupboard. My mother so detested this chemical staining the plug hole of the kitchen sink, one day she asked me to dispose of it in the garden for her.

I poured it into the soil adjacent to the garage driveway, the place where Dad had a rubble sump where he disposed of old engine oil from time to time. Instantly, earthworms popped out of the ground. Their speed to escape this solution was shocking, I have never seen worms move so fast. I was shocked and grabbed them all in a handkerchief and rinsed them under a running tap in a colander.

While my mother was infuriated by my misuse of cooking equipment and a clean handkerchief, I had learned a valuable lesson.

I kept lizards, turtles, frogs and toads. I had been told not just feed them exclusively on mealworms (which I kept and raised in bran), so I supplemented their diet with earthworms.

During the prolonged and severe droughts in SE England of 1975 and 1976, earthworms dug so deep into the soil it was impossible to dig many out of the vegetable garden. Instead, I used a very dilute solution of potassium permanganate and poured it into a small section of lawn. With a bucket of clean water by my side, I waited. After a couple of minutes, out of the turf erupted worms. Into the clean water they went. Rinsed clean, my pets had supper. Then I flooded the soil with clean water to avoid harming the turf with this reducing agent.

In Britain, Condy’s Crystals was never widely adopted, but fast forward to ABC gardening talkback radio in NSW in the mid-1990’s, and I heard a reference to using it as a garden fungicide. I had to look this arcane term up – and learned it was a trade name for worm-unfriendly potassium permanganate.

There are more effective organic fungicides available to gardeners than than potassium permanganate that no worms need to suffer from spray runoff.

I’ve been doing regular radio gardening talkback since 1995. I try to coach gardeners to garden consciously and sustainably. Those who listen to me, or who have followed my advice on organic fungicides on television or expos already know that my grandfather’s 18th century rose fungicide is extremely effective at controlling rose rust, rose black spot and mildew. Following horticultural trials in NSW in the 1990’s, Grandad’s Rose Fungicide Recipe has been commercialised in Australia.

Putting feeding amphibians during drought aside, the effective organic management of plant health does not need to harm worms. Also, thanks to modern medicine my toes can be fungus-free and remain spotless.

Is potassium permanganate totally redundant? No. The crystals, correctly stored, last indefinitely. Add a few bottles to your doomsday prepper medical cabinet shopping list, just in case. Surgeon’s still use it.

Jerry Coleby-Williams
9th April 2025