I just replaced all my cactus soil and now I have a ton of white mold growing all in the pots especially the one that had several cacti in it. Two of my cacti rotted and I've cut off the infected part in hopes I can maybe save them. The others I pulled out and they had mold on the roots but I wiped them with peroxide, dabbed them dry and I'm going to let them air dry. Now I'm thinking I should probably take out all my cacti out of their pots to let them air dry as there could be mold that I can't see under the soil. Why is this happening? Is it because the soil was still damp when I put the cacti in?? I've done that before and had no problems. I was dealing with some sort of fungal issue already that's why I did the soil change. Should I get fungicide?? This is getting really bad as I don't want all my cacti to die especially the baby barrels. I have oxalis that I'm trying to grow too and I don't want the mold to get to them either. What do I do???

Update! I took my golden barrel cactus out of the soil and to my despair it was completely rotted through! :'( I noticed though that when I took it out of the soil, the soil where the roots were was still wet. I'm assuming that's part of the issue. The water retained in the soil around the roots and rotted out the roots. I'm still unsure of the mold though. Luckily I so far have been able to save my Townsend barrel (that one I care most about). This situation is really bad though. Should I just buy a completely new bag of soil and maybe from a different company and buy some fungicide as well?? And should I have waited for the soil to be completely dry before I replanted my cacti???

Oh I also forgot to mention. Yesterday I had left my window open all day and it was extremely wet and humid out. Could that also have something to do with the mold??

Alright another update. I took all my cacti out of the soil and dumped all of the soil. Pretty much all of the soil in all the pots were still wet in the middle. I had those sitting in a room with a dehumidifier for about a week and the soil was still wet. Only the very small pots I had with the very small cacti I have were completely dry so those should be fine. I'm starting to think though that there might be a problem with the soil I have been using. I noticed that the soil has barely any rocks/pebbles/stones in it and it's mostly wood chips which I'm pretty sure retain quite a bit of moisture and can get moldy quite easily. Hell, the oxalis soil I had bought has more pebbles in it than the cactus soil I have been using. The soil is the Miracle Gro premium succulent and cactus soil mix. I think I should probably get a brand new type of soil. Are there any recommendations for good cactus soil brands??

to the forum!

I can't solve everything but I'd like to offer a few observations.

Whatever soil sprouted white mold all over it shortly after use should be avoided in the future. I don't know if that even affects the plants, but it's kind of a bad sign. So make a note of that. And clean your pots well after this episode, with plenty of soap or even bleach.

A huge variety of soils work for succulents indoors. At some point you need to learn how your soil behaves and adjust your watering accordingly. During the growth season, you want the soil to cycle from properly wet to mostly or fully dry. However long that takes, you wait. Then water well and repeat.

The most useful soils for cacti drain fast and dry out relatively quickly. This is primarily determined by the amount of rock in the soil. A soil mix of half organic, half inorganic (rock) is a good starting place. If the soil you buy comes with rock already in it, great. If it's mostly or all organic, add perlite or pumice (but not vermiculite or fine sand) to get it in that zone. And try to be consistent, generally.

Small pots will dry out faster than larger pots, as you have observed. This is because the water holding capacity is related to volume, but the rate of evaporation is related to the surface area of exposed soil. If you don't want a different watering schedule for every pot in your collection, you can just water the bigger pots half as often, simple as that, and that will nudge things in the right direction.

Mold and rot are treatable conditions (up to a point of course, and very much depending on the type) but they are far easier to prevent. That is where you will get the greatest benefit from focusing your attention and energy. Lots of light, lots of air flow, a good watering schedule where the soil goes properly dry at depth (not just at the surface, which dries out much sooner). These problems tend to take some time to set in, not just having the window open for a day.

I would recommend against unpotting and manipulating cactus roots unless you have a very specific question. You can figure out the moisture content in the soil without unpotting a plant. To whatever extent you may damage the roots by separating them from the soil and handling them, you may make the problem worse, not better. In any case, wait a week or more to water any plant that you bare-root or have otherwise broken roots.

Edit: haha, seems like posted almost at the same time as Baja's, as there are some contradict suggestions, I deleted my post to prevent confusion.
And I can assure you that I trust Baja the most in handling cactus succulents.

Welcome to the forum

Hello Ace, and welcome to the forum.
I'll start with a couple of questions--
Where are you located?
Are you growing cacti indoors or out?
Can you post a picture or two?
I've used the MG cactus/succulent mix, but just for succulents, and mixed with up to 50% additional grit. For grit, I've used well rinsed pumice, poultry grit (chipped granite), or pea gravel with good success. I don't care for perlite.
For potted cactus, I've switched to Bonsai Jack's Gritty Mix. It does not retain water, and I don't think it would support mold growth of any sort.
Fungus is everywhere. Soil fungus is not necessarily a plant pathogen. Treating with a fungicide will not, in itself, keep a cactus healthy. Your growing conditions are favoring mold growth, not plant health.
In my experience, desert cacti are difficult to keep as houseplants. They like long bright days, and hot (80F.+) dry weather. Even with heat mats, grow lights, proper soil and watering it's hard to keep them happy indoors.
Some do best by letting them go dormant in Winter, keep them dry and cool through the short dark cold days.
IMO I would not use peroxide on plants. It kills cells by oxidizing them. It doesn't know the difference between a fungus cell and a cactus root. I think it does a lot of damage. I recognize that others disagree. (Peroxide is no longer used for wound care, it prolongs healing.)
I hope you will hear more from the cactus experts here!

I'm pretty sure I had no other choice but to unpot them. The soil was completely filled with mold. Mold all over the roots. Three cacti rotted and two others had rotted previously. If I didn't get them out they probably would've all died. And I need completely new soil too along with letting it dry out before potting the cacti. The soil had even smelled very strongly of mold. I'll get soil very soon so they're not sitting out for very long. And I know the problem wasn't my watering. The soil was already wet since I bought it. I had always been very careful with my watering and I always waited several weeks before watering and when I did water, I wouldn't even soak all the soil especially in the big pot. I'm sorry if I sound rude. I'm not at all trying to be. I'm appreciative of your help

My point about watering is you need that wet-dry cycle to occur. The soil really should go fully wet (during the growth season, say spring-summer, north of the subtropics) and then dry or almost dry in between every time (ideally, conditions permitting) or most times (in the real world). During late fall and winter the cycle will probably take longer (shorter, darker days and lower temperatures) and you should change your watering accordingly.

The degree to which winter affects your plants is mostly determined by latitude, in a reasonably mild indoor location. In the northern US or Northern Europe you may want to withhold water partly or completely during winter to achieve a state of suspended animation until the light improves. Here at 32 degrees N latitude I do not water my indoor plants less often in winter, and that's because they can "see" the sun for hours a day, with no obstructions in a southerly facing window. But that may not work for you.

You haven't provided much information about your location or the light exposure where your plants are.

@MsDoe
For some reason my message sent after yours? I was replying to the message before. I'm in IL and I keep my cacti indoors. That sounds like a good idea to make them go dormant in the winter. I'll also look into the soil you mentioned. I would've posted a pic earlier of the rotted cacti and the moldy soil but I've already dumped all the soil. Sorry!

@Baja_Costero
I'm in IL and keep my cacti indoors right by a window. I actually did limit the watering in the winter, I should've mentioned that before.

Right by a window is where you want them. What direction does the window face? Are there curtains or blinds or obstructions outside? Can they "see" the sun (line of sight to the glowing orb in the sky) for hours a day, year round, weather permitting?

@Baja_Costero
Yes, they get sunlight all day and I keep the blinds open all day so they don't block the sun. Where I keep them is one of the sunniest spots in the room.

What direction does the window face? I can guarantee you they don't get sunlight of the type I was referring to (which is the kind that matters) all day. It's not really possible.

From personal experience, I think MG changed their soil mix, both the cacti and regular potting soil. The new batches seem to contain more organic material that retains moisture too long and is very dense even when cutting with gritty material. I've recently lost a few cacti and succulents as well so I feel your pain…..

@Baja_Costero
The window is facing west

Hello Again, I think I was typing while Baja was posting, sorry for any confusion.
Watering indoor plants is more complex than it seems at first. Here are some factors to consider:
Potting mix
Pot/drainage
Pot size
Temperature
Humidity
Air movement
Type of plant
Light exposure
Growth phase (growing or resting?)
Water hardness and pH
Oh yes, and BTW, water amount and frequency.
I'm sure there are others.
So there's no easy answer for the "how to water" question.
Also, it's ok for most cacti and succulents to be un-potted and dry for a week or more. Don't feel like you have to pop them right into new soil, they actually do better with a little time to rest and dry out.
Once they're re-potted, don't water for at least another week.
If you're interested, here's a link to an article you might find helpful, scroll down to page 8:
https://centralarizonacactus.o...

Ok so I looked to see if I had any pictures of all my cacti and I don't have really any. All the cacti/succulents I had were: Scarlet Hedgehog, Golden Barrel, Townsend Barrel, 2 Eve's Needle, 4 Joseph's Coat, 2 Eastern Prickly pear, a baby Pearl Plant aloe, another baby cactus I don't know the species of, string of turtles, dragon fruit cacti, powderpuff cactus, mother of hundreds cactus, bishops cap, and a common fishhook. The bishops cap, common fishhook, and golden barrel have died from rot. The golden barrel died yesterday and the bishops cap died a few days ago.The powderpuff and mother of hundreds have rotted but I cut them, I have no clue if they're going to make it or not but we'll find out. I do luckily have seeds from the mother of hundreds though. Before all of this I had a very large powderpuff cactus that had gone completely moldy and died and shortly after, the common fishhook died. I had also had a bad mealy bug problem a while ago which I was using alcohol to kill the bugs which actually worked. I'm thinking though that when I was doing that, I might've been putting too much water in the soil as alcohol has water in it and that's probably what killed the large powderpuff I had and then it was a chain reaction from there I'm assuming. I should've also mentioned that my one eves needle cactus' small offshoots had started to shrivel up and die off which then they'd just fall off.

For what it's worth, a west-facing window will not be as bright as a south facing window, all things equal, especially during the darker months. I don't know if you have that option, and obviously you need to work with what you've got, just thought I would put that out there in case there are other windows available.

@Baja_Costero
I do have windows that face south but there's unfortunately no where to put cacti by them. I would if I was able to