sick cactus

My cactus has had this brown spot on its side for a couple weeks now and I don’t know how to fix it. I think it happened when I was away for a month and forgot to have someone care for it. The house was colder than normal (55 degrees F) and outside was very cold. How should I fix this? I water the plant once a week and it sits by my window to get as much sunlight as possible.

  • Was the soil wet when you got back home? Was the side that's showing damage nearest to the window?
    – Bamboo
    Feb 9, 2018 at 0:22

1 Answer 1


It either had rot or is still actively rotting from the inside out. My guess is too rich of soil and too much water. It happens....

Cactus exposed to cold would more likely be marked on the top over a fairly wide field, not dots on the lower side.

The good news is the rest of it looks pretty good, not awesome, but nice and green. Look at the very top/apex and see if there are any new spines (this where I look for new growth, it's easiest to spot here). New spines = good news. No new spines still not cause for concern at this point.

If this were my plant, I'd leave it until the soil has dried out completely. By that time it will have either rotted in two or started growing. (Assuming the days are getting longer where you are.)

Long term, I would pot it in mineral-based soil and water when it needs it.

Good luck!

  • Thanks! It looks like new spines are growing I think. How long does it take for the soil to dry out completely?
    – Jake Moran
    Feb 8, 2018 at 22:55
  • It depends on local conditions, primarily temperature and relative humidity. Have the brown spots stayed the same size or shrunk? Once it dries out, get a sense for how heavy the dry pot and plant are. Then when you are thinking about watering you can "weigh" the pot/plant to get a sense for how much water is retained. That method is understandably imprecise and also isn't useful for large or heavy plants, but it's another data point for when you are deciding to water or not.
    – Tim Nevins
    Feb 12, 2018 at 17:33

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