Hi everyone. Are these black spots on my Opuntia robusta cutting rot or cold damage or something else? I noticed them about 3 days ago. We've had nights dipping into the low 20s F, so I moved many things up onto my covered patio including this cutting. I had thought I had it far enough back to not worry about frost. None of the black marks are oozing or soft or smell rotten, they feel more or less like the healthy green tissue does. They have also not grown larger but a few have gotten slightly darker. When I shook it loose and pulled it up to take a look, it had grown roots (I planted it 2 weeks ago) and there wasn't a single black mark anywhere on the half of the pad that was buried (it was planted standing up). The bottom 2 or 3 inches of soil in the pot were slightly moist, but it rained here a few days ago and I may have had rain blow onto my patio and possibly been wicked up by the pot, or the water that ran down the patio when I watered my mints. None of my other potted cacti or cuttings are doing this, including two other Opuntia robusta that were set only a few inches away (the other 2 are not cuttings however). Any thoughts?

Opuntia do root really fast - They start rooting in less than a week whether planted or not.

Do you think those are wounds from being poked by something (like another cactus)? They don't seem to be rotting and some may be healing.

I agree with Daisy that it almost looks like some kind of damage, maybe from insects. If it does not expand I would not be too worried about it. It looks like the plant has some roots, but is still working on developing a bigger root system, so that might make it more susceptible to wet related maladies... Keep it as dry as possible.

Low 20s is on the lower limit of the plant's reported cold hardiness, wetness likely makes it less tolerant to cold. So it could be very localized frost damage - maybe in spots where the plant had some damage before, where the outer skin was not as 'robust'. Frost damage sometimes does take a while to show its full effects, but if you have not really seen any changes in 3 days would suggest that whatever it is, this is the extent of it.

If you really want to check if it is rot, you could cut into one of the spots and see what the condition of the flesh of plant is in those spots.

We rarely get low 20s where I am at, only once for a 3 day period in the 10 years I have lived in the greater Phoenix area, any time I have had frost damage on PPs - I have a bunch that will get some frost damage in the high 20s - it has been superficial and the plant will rapidly grow out of it once the growing period starts.

I have been amazed in the past Daisy, it's incredible how fast some of them will send out roots. I've had fresh cuttings drying in the shade that have sent roots out from parts of the pad that aren't even in direct contact with the soil! I wondered if one of my other cacti had poked it at first too, but the pot is higher than most of my other potted cacti and the ones that are taller were placed elsewhere on the patio. The only other damage I could imagine happening was perhaps some wind blown debris. Maybe even a bird?

Thijs, it is interesting you mentioning some of the skin being less robust than healthier parts of the cutting. When I first received it, it had an area on the side of the pad that was a slightly different shade than the rest of the pad, and when you pressed this spot it had a bit of a "spring" to it. You could feel the skin press down, but the moment you lifted your finger the skin would snap back up. I suspected at the time that it was perhaps some damage that happened from a rough transit, and that spot later developed a callous. I wonder if these black spots are damaged areas that were merely more susceptible to cold damage when our temperatures bottomed out? A few of them have that same "springy" feel. The flesh is not soft but is slightly pressable and snaps back up when you remove your finger.

Phoenix has just about perfect cactus weather I think. Our winters seem to keep many cacti from reaching their full potential. There are a few in-ground myrtillocactus around here but they get horrible frost burn each year. And probably half of the houses here have Opuntia ficus-indica in their yards, but they usually are only between 3 to 8 feet tall at most and perhaps 6 feet wide or so and more shrubby than arborescent. Never the giants that they can grow into in your area.

Hi Paul, oh, you are getting the low 20's already..we get that here in Jan sometimes. It is possible with the increased humidity in the air plus the rain that comes intermittently, even if it is positioned way to the back that it is getting cold damage especially when temps are going that low. Just try to keep it as dry as you can at soil level. As long as it is not starting to sag or those black spots do not spread, then the plant will just slow down and heal, but a rather slow process when it does it, since it is quite cold.

Thanks for your input, Tarev! Hopefully I don't have anything else develop these spots. It's rained all day and it's still wet outside, the temperature is already in the 30s. So we have humid and cold tonight! Fortunately there is also wind. I've started bringing this cutting in at night just to be safe. I am starting to try and grow more things during our cooler weather and there is a learning curve for someone who is used to growing things in spring and summer

I got some succulents more active right now as well, makes me realize just how patiently they wait for the intense heat to move away, so they can resume growing. So funny to watch one of my Aeoniums go wishy washy..it can tolerate the cold, but when it rains, it is quick to droop.