Hello everyone! I happened to overwatered my cactus after having repotted it without much preparation (it was originally in a pot with two other ones, which is how I brought it home, but this big guy was pushing out one of the littler ones). Two weeks later, I found it wobbly and thought I didn't pot it deep enough in the soil. That was three days ago. Today, I found it flopped over (!) and decided to take it out. Turns out it exploded near the base. I removed some of the soil with the help of water, and I'm letting it out to dry now. It still looks a really healthy green up top, but am afraid it won't be the case soon. How do I tell if the roots or any places are rotting? Any kind of help/pointers would be greatly appreciated! What is the best way to approach my sad cactus right now?
Take a sharp, sterile knife and make a straight, clean cut across the remaining fleshy part of the cactus, just above where the shrivelled part is. Dust the cut with cinnamon and allow this to callus over for a couple of days. Then pot into fresh DRY soil and ignore for a month or two.
Root rot. Check carefully for dark brown, black or reddish spots on the cut surface (they should not be there). Normally you will have to cut higher up (several centimetres) than "just above where the shrivelled part is", because the disease spreads along the vascular tissues, the effect on the surrounding tissues comes later. I think your plant will be difficult to save. The wound might be too large relative to the remaining volume when the infected parts have been removed, and if so the cutting shrivels and dies (I have experienced that ...). When I only have a small piece to work with I usually graft it, but it is the wrong season for that. You did not water it directly after repotting, did you? Anyway, it should not have needed any water now, it should be dormant.
When I repotted it the soil was wet... actually the soil was probably bad as I just used whatever was lying around (for who knows how long). Hence the rotting. But I will try what you have suggested, and see if it will turn things around. Thank you.
Pathogens are present in almost all soils, but it is difficult for them to attack the roots unless there is moisture and an entry point. Damaged roots (and they are always damaged when they are removed from the old pot.) provide both, and if the soil is moist and has a high content of peat the risk increases substantially. I always let my unrooted cacti lie on a piece of paper for at least a day (more for sensitive species) before repotting them in bone dry soil, then I don't water them for about ten days.
I haven't had the chance to update, but here's what it looked like after I cut it. The hole was really deep, making it pretty much hollow. I knew it can't be salvaged... A few days later it has shrunk and shrivelled up into all it's left. Anyway, my other two seem to be doing fine. But I notice some, what looks to be tufts of white stuff, in the crevices on the surface of the cacti. I'm thinking if it could be mold? It didn't appear until recently, probably starting November.
A fine example of well-developed rot and what I meant when I wrote that it spreads rapidly in the interior of the plant. :( I have seen mold on the surface of cacti, but it has always been growing on dark patches on the skin (and when it has gone that far it is too late). Sometimes white hair from the areoles end up at the bottom of the "crevices", but that can be blown off easily. Do you have a picture?
I can't blow it off. I picked some of it off with a tooth pick, and you can see that it's fluffy. Near the bottom of the round one without the flower (sorry I don't know their ID/species), the white crusty-flaky-looking stuff is the sappy material that it once secreted before and then dried up. Thought I don't know why it was doing that... I'm just concerned about the appearance of the white fluffs at the moment.
Some of the white stuff is hair, it is supposed to be there. There are a few bigger patches that look more like mealy bugs and their eggs, photo DSCN8691 is a good example. If it is, kill them. Quickly. The "sappy material" was probably just white sap. Both plants belong to the genus Mammillaria, and the one with the sap could be a M. geminispina or parkinsonii (I am not good at identifying Mammillaria), and they are known for their white latex, as can be seen here. The other plant has a fake flower, by the way.
Thank you, mandarin. What is the best way to kill off the bugs? And how do I prevent them? It's also been about a month since I watered them, so I think I will be doing that soon. Would they need fertilizer at this time of year, or how often would they need it? Thanks for all the help! I'm learning :)
Depends on who you ask and what you have access to. I remove the big ones with tweezers, spray the plant with ethanol or isopropanol (to kill the eggs and the smaller ones), and finally spray or water (depends on whether the plants are active or not) them with a systemic insecticide (one that enters the plants and makes them toxic to sucking insects like mealies). Some use horticultural oil or soap spray to control them, but I have almost no experience with that. By not letting them in. They typically come with new plants as they are very common in flower shops, garden centres etc., so it is important to isolate new plants until you are sure they are free from pests both above and beneath the soil surface. Some of them feed on the roots (root mealy bugs) and can be hard to spot and kill. I don't know if they can survive outside in my climate. I doubt it, I have never seen them on wild plants. Some growers treat their plants one–two times per year as a preventive measure. I don't, except that I sometimes spray all the plants with slightly diluted alcohol. I only treat my whole collection with stronger insecticides if I discover root mealies on a plant, as they are the pest I fear most, besides red spider mites. No fertilizer, there is not enough light. I only fertilize mine in summer. I stopped watering mine in September–October, and I will not start watering them again until April–May, to prevent them from growing when there is not enought light. Further, it makes them less prone to rot. I keep them cold (1–15°C), and they rot easily if cold and wet. The only exception is a few species that do better in room temperature with a little water. I keep them cold because it is easier to keep them dormant, and many species flower better after a cold winter rest. If your plants are warm i winter they could use some water once a month or so. Watering a cactus in winter is not easy however, it may result in a rotting or etioliated plant.
