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by Andrew S.
(Ithaca, NY)

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So, my friend recently moved and one of her plants is growing a little mold it looks like.

She was very surprised by it so I do believe this is the first time she’s ever seen it. Her old apartment got a lot more sun than her new place, so she is learning that she needs to water the plants much less.

Any thoughts as to what this may be, and what to do about it?

Drought Smart Plants reply:

Hi Andrew – I would say that anytime you see mold at the base of a cactus, it’s never a good thing. Mold needs moisture to grow, so this indicates that the soil is too wet for the cactus to be happy.

The type of mold is actually liverwort, which is worrying, not only because of the name, but because it tends to block off air and moisture to the roots of the plant. These can be scraped off, as their roots are very shallow.

After scraping off the liverwort, I suggest using a mulch of pebbles or my favorite lava rock placed around the base of the plant. I would normally suggest that the cactus be lifted out to check roots so you can try that just to make sure that the soil isn’t too damp.

Cactus, like all other succulent plants prefer to be dry, then have a good soaking only two or three times a year. I’ve heard of an avid cactus collector who watched the weather reports from Tuscon, Arizona, and only watered their collection when it rained there.

Overwatering is the leading cause of death in succulents and cacti, so err on the side of not enough water, rather than too much.

Also, always use tepid or lukewarm water, preferably rainwater rather than out of the tap. I find that tap water from our well for instance, has too much mineral content, and if you’re not flushing the soil completely through each time, salts can build up in the soil.

This is not a good thing. Occasionally, if you notice salt or mineral build up, buy some distilled water from the drug store to flush the soil thoroughly, say once a year.

I notice in the pictures that the pots these cacti are in are glazed pottery – I recommend using unglazed terracotta clay pots, as these breathe and allow excess moisture to escape through the porous sides.

Happy Cactus Growing!