Name: Phillip williams
|As a microbiologist, I might suggest that since your pots are exposed to the sun, at least part of the day, and given the speed with which the discoloration seems to reappear after washing, that what you may have growing on your pots is not mold but algae. Algae is always some shade of green. I know of nothing that you can use to prevent algae or fungal growth on your pots (for any length of time) which could not also possibly harm your plants. The use of a chlorine wash on an empty pot will work, but only for a short time until nature reinoculates the pot.
Albuquerque NM, Elev 5310 ft (Zone 7b)
Answer from NMoasis
September 30, 2017
|Michey, if I read your question correctly, you are looking for a way to keep the pots looking "pretty" while the plants are still in them, in which case the above suggestions for soaking in detergent or bleach aren't practical. Try wiping the exterior of the pots with plain distilled white vinegar. While I haven't tried it on pots, it works wonders in my concrete birdbath, and also seems to have a residual deterrent effect against mold and algae growth even after it's rinsed off. Plus, less toxic for all parties.
Name: Greg Bogard
Winston-Salem, NC (Zone 7a)
Answer from Sscape
September 30, 2017
|I agree with NGA about the look of old, weathered pots. However, if you reuse these pots, and there is white, slimy mold on them, it would be best to wash that mold off. That kind of mold can run rampant and cover the roots of your plant. That would not be bad except for the fact that the mold waterproofs the roots--so they can not absorb water. Your plant will die from dehydration. The best way to get rid of that mold is the first suggestion: 50/50 water/ chlorine bleach. After the soak and rinse---let them soak in straight water for an hour or two to get the rest of the bleach out---then let them dry completely before you use them.