I have been searching the net for some clues about a cactus – I have no idea whether it is suffering from lack of water or too much water! It is a tall, silvery blue-grey cactus with side branches (we were told it was a ghost cactus when we bought it). It does not have large spines.
It has been healthy for 2 years and we have been very careful not to over-water. However, today one of its stems is shrivelled at the bottom and has flopped over. Higher up on the stem is an area which has gone soft and brown – almost as if it has rotted. There are a few drops of sticky, milky white sap on one of the other stems. The other stems all seem fine at the moment.
I did give the cactus a little bit of water a few days ago, but not enough to drain through the holes at the bottom. I have felt the soil today and it is dry as a bone.
I am too afraid to water it as I know it is easier for a cactus to recover from under-watering, and thought I would seek advice first!
It does not seem that you are overwatering, so that is probably not what has caused the arms to rot.
You will need to treat the rotting areas right away to keep it from spreading. Cut off the dead branches, making sure there is no rot left on the remaining portions, and spray with household peroxide. You will probably need to cut out the area in the middle of the branch, and also treat it. However, before you do all this, if the plant is a Euphorbia, you will need to be careful not to get any of the milky white sap on you, as it is caustic. Can you send a photo, so we can see if it has an infection, and what type of plant it is.
Finally, how much light is it getting?
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Thanks for the quick feedback. I am attaching some pictures of the ghost – I believe it is the Euphorbia trigona – but unfortunately I had cut off the bad stem before taking the pics.
I cut the stem down at the base – one of the pics shows the remaining dry part. I cut the rotted piece out and have saved the rest of the stem to try to grow some cuttings. The rest of the plant looks good, but one of the other stems feels a little soft in 2 spots. I am hoping it is just lack of water, since I have been so afraid to overwater!
I would also like to know the proper time and method to repot it, as it has been in this same pot for 2 years. I assume winter is not the right time but I would like to plan ahead.
You’ve got a Euphorbia lactea “Ghost”. The plant that is left in the pot doesn’t look like it has any serious problems, as best I can tell from the photo’s resolution. It sounds like you took care of the problem parts correctly.
For the cutting you have now, I would recommend rooting hormone, dry soil, and heat because we are heading into winter.
I recommend watering every 4 to 6 weeks through winter, and every 2 to 3 weeks the rest of the year when it is growing.
Repot the whole thing this spring, in fresh dry fast-draining cactus soil.