How to clean clay pots

E’s problem with fungus on a pot brings up the topic of reusing clay or terracotta pots. If you reuse your clay pots — and I can’t imagine anyone who doesn’t — a simple once a year cleaning can help keep any mold, fungus or mildew spores from spreading.

First, know that a fungus is different from the minerals that leech out of the water and leave a white-ish coat or moss that leaves a lovely green coat. Many people don’t want to wash their clay pots and remove the aged look it takes time to acquire. It’s kind of like brand new tennis shoes that are stark white.

But if you want to clean your pots, here’s how:
To remove white salts/mineral deposits, coat with a baking powder and water paste, scrub with a brush and then rinse with plain water.

To clean and disinfect, scrub the inside with a brush to remove built-up soil, then soak for 30 minutes to an hour in a tub of water filled with 1 part chlorine bleach to 9 parts water. Do not add soap, just bleach. If needed, scrub the outside of the pot down. Transfer the clean pots to another tub filled with clean water. Let the pots soak for 30 minutes to help dilute the bleach that remains in the clay, which could harm sensitive plants. Place upside down to air dry.

Help! Q&A

E. from Beaumont emailed in a question:

Q: “Everything seemed to be going well with a new African violet until a couple of days ago, when I noticed that its pot was molding or mildewing or something. It had gray "fur" -- the same look that improperly dried-out shoes might have -- spotted around the pot itself. Another pot, also in a north-facing bay window doesn't have the problem, but it is not planted in the same batch of soil. The pot does not sit in water and the light it gets is filtered through white Roman shades. The air conditioning stays at about 76, rain or shine. What gives – and should I be worried about the plant?”

A: Bottom line? If it’s fuzzy, it’s fungus. So how did it get there when the other plant is doing fine? There are four pieces to this puzzle: clay pot, potting soil, Roman shades and sunlight.
To have fungus, you have to have spores. Since the clay pot was new, it likely came from either the original container you bought the young violet in, or the soil. Both of these are possibilities, since the healthy plant is one you grew and the fuzzy pot contains a plant you bought. Since you didn’t use the same soil in the affected pot as you did in the clean pot, it’s suspect.

Adding to the right conditions for fungus growth are the light conditions (the sick pot is in the same window as the healthy one, but on the side that gets less sun). The heavy filtering from the Roman shade might help your electric bill, but it’s not helping the violet. Also, the clay pot allows water to seep through, adding the moisture the fungus needs to grow.

What to do? Sponge the outside of the pot down with a 10% bleach solution. It should kill the fungus. Place the pot where it will get more light. If after that, you still have a problem, you can try re-potting it in clean soil, but you likely won’t get rid of all the spores. In that case, hard as it is, ditch it and start over. Be sure to toss it in a plastic bag and seal it before tossing it out. Don’t spread the spores in a compost pile. If the pot looks clean but the plant starts looking diseased, toss it.