We've had this beauty for about two years, and when we went for our monthly water, noted discoloration at the tip of one limb and the base of that trunk on the " backside" (facing away from light). The flesh is soft in part of the discolored area but not most. I fear we have root rot but we water once a month and it is in a well draining pot, and then the discoloration and shriveling at the tip seem to be the opposite problem, not enough water or light?? Any advice would be very much appreciated...we are dedicated succulent parents and this is making us so sad.

THANK YOU!

It does not look good. There is rot in the stem if the softness and discoloration spreads. You can still try to rescue the plant as a rooted cutting at that point, but the underlying conditions which led to the current situation need to be addressed. I am guessing the main problem is a lack of light, which can be a serious issue for several Euphorbias. Does the plant "see" the sun for hours a day, year round? Is there a brighter position right next to a sunny window where you could relocate it?

Thank you for the quick response! Yes we have western facing windows so he gets a lot of light but limited direct sun, especially in the winter being in Colorado. We could move him to a different floor with more direct sun for the time being...or get a grow light (far enough away not to burn him)...but would you first recommend unpotting to examine the roots and cutting off any soft parts? Thank you so much for your advice.

Yes, if the plant can "see" the sun, that would be better. Reflected and diffused light is great indoors but it's not an good substitute for a line of sight to the sun. This plant is actually kind of needy about strong light. I don't think that dialing up the light will necessarily save your plant at this point, though it can only help, and it will probably be necessary for any rescue to be successful.

I don't think you're going to get anything useful out of unpotting the plant. If the rot is already in the stem, it will tend to progress upward until it eventually consumes everything. There's some chance that what you're seeing does not progress, so don't give up hope right away. But unpotting the plant will only damage the roots further and stress the plant out more, without solving the core problem of the rot invading the stem itself.

The best route to a rescue would be to restart the plant from a cutting taken where the stem is still solid and green. Using a sharp knife, cut straight across the stem (anywhere that it is healthy, a safe distance from the discoloration). Avoid touching the sap and especially getting it in your eyes (potent irritant), and clean your instrument carefully afterwards, while the sap is still wet. Leave the cutting in a bright place to heal for a week or two, then pot it up with just enough stem buried to provide the necessary stability. Use potting soil mixed with an equal volume of perlite/pumice/etc. as drainage is very important. Wait another week to water and then probably monthly from there until you see new growth on top.

Since one arm is also discoloring from the tip down, would you take the cutting from the upper 1/4 of the taller trunk? So sad to lose so much of the trunk where it appears to be healthy to get above the discolored / rotting arm.

And, what would you do with the second, shorter main trunk that is showing no signs of ill health? Thank you!

In theory you could try to extract the left stem with the discoloration entirely from the container, leaving the healthy one behind. But I worry that you'll just end up breaking roots and spreading rot all around in the process, which would might defeat the purpose. If you think you can separate them, go for it. Be gentle, and try to treat the rot as a contagious agent to be limited and contained.

For the purpose of rescue, I would take the tallest stem all the way down to the branch point, cutting at the narrowest point in the stem just below that spot, and with the one discolored branch removed at its base. You'll get a branchy cutting that should root pretty easily.

Your Euphorbia looks like E. ingens, a truly massive tree when allowed to stretch out in the ground. You cannot provide too much light to this plant indoors, given mild temps and good air flow. It tends to have a seasonal growth pattern (each "segment" in the stem represents one year of growth) and when started from a cutting, it may take some time before it starts growing (including potentially skipping a season). So do not panic if your cutting sits there apparently doing nothing for a while.

All right, thank you again! The rescue mission is underway. We have the two main trunks isolated and the taller one cut and laid in the sun for callousing ... perplexingly, the roots overall looked healthy, especially in the shorter trunk. Our plan is to repot that separately with roots intact. Should we wash the roots of and spray with fungicide before repotting?

I don't think that's necessary, given how you have described things. You can rinse them in water but even that is not really necessary. If you do rinse the roots, give them time and air flow to dry out completely before potting them up. And remember to be careful not to water deeply until a week or so has passed, so the roots have time to heal after being handled.