Question
Euphorbia hermentiana/Euphorbia trigona:

I have had this cactus for probably 10 years.  It is about 5 feet tall, more than doubling in size since I purchased it.  I have NEVER repotted this plant in fear that I would kill it, as it is one of my most PRIZE posessions.

I recently got up the nerve to replant it, as they stalks and new arms were getting more and more crowded, about 3 weeks ago....  I bought special CACTUS soil, "SCHULTZ PROFESSIONAL CACTUS AND SUCCULENT POTTING SOIL" with a similar cactus on the front of the package, as was confident that I would succeed.  Unfortunately I am not cactus pro.

I FAILED!!  My cactus started rotting from the base.  The moment I noticed, about an hour ago, I pulled out the knives and began surgery.  I have cut off all the rot, a couple inches above, and now have the patients on the kitchen table awaiting your recovery instructions.  

I have read on so many websites different suggestions and as these as my PRIZE POSESSIONS, I want to do what works the first time.  Please note I also have about 3 feet left of 100% healthy stalk here, on one, maybe a foot on another and maybe 2 feet on another..... all 3 stalks had began rotting.

I know I am not supposed to put these in anything besides an empty pot for probably three weeks.  Did I plant these to deep in the soil? Could there be bugs?  <--I didn't see any.  The water was VERY MINIMAL, the soil does not feel wet.  It feels the same as the day it came out of the package.  The cactus soil I bought doesn't seem anything different than any other soil I have ever used.

I also read to plant them in 100% sand.  Others say to mix sand with the cactus soil.  I have play sand, is that the sand they are referring?  Steer me in the right direction here.  I have been reading your suggestions all night and you seem like the cactus GOD right about now.

Thanks Greg, I would be great if I could hear from you in the next three weeks!

Answer
Dear Rebecca,

It sounds like maybe your plant got "bruised" or damaged during transplant. You need to be very careful when dealing with Euphorbias as the sap or latex can be very poisonous.

It is the latex that spreads rot through out the plant very quickly. Anyway, let the cutting dry for at least a couple of weeks and make sure the cut end feels hard before replanting. Plant each cutting about 3 to 4 inches into the soil and water after planting. Make sure only to water when the soil is dry after that. It may take a month or more to root so be patient.

You can use "cactus mix" soil and add a about 1/3 sand (play sand is fine) to the mix. Do not expose to direct sun, but keep it in very bright light. You can also use a product called "Superthive", which is a root stimulator. Just follow the directions. Hope this helps, and great question by the way! Hope this helps and good luck!

Sincerely,

Greg