Question
I got two of these cactus that were rootbound in pots. I replanted them in bigger pots, using cactus soil around the base about 1-2 inches around them, and filled the rest of the pot with regular potting soil.  I water them 1-2x / month, they are inside @ ~80 degrees. The base of both of them is turning yellow - is that because of shock, not enough water, or too much water and not allowing them to dry out totally between waterings? The regular potting soil may not allow them to dry out - and I do not have holes in the bottom of the pot to allow the water to drain, but their previous environment allowed them to drain totally when watered, then sit in a small amount of water.

Answer
Dear Margaret,

It is hard to say with out a picture.  I suspect you have rot.  Are the yellow areas soft at all?  If you repotted in A.) soil that doesn't drain well and is not sterile and B) don't wait a week or two to water after repotting you set the plants up for disease or fungus.  Why did you use regular potting soil? It isn't light enough for a succulent.

When you put a plant in a pot with out a drainage hole you really need to be vigilant about watering. I use a wooden skewer and don't water unless it is completely cry.  Some folks use water meters but I find they are too large to insert into the normally crowded pot and I'm afraid it would damage the roots too much.

Euphorbias are winter dormant so very little water is needed at this time.

If they were my plants I would check for rot, take some cutting from off shoots if the plants have them and then. If there isn't rot I would let the plants dry out for a few days at least and repot in a soilless mix (preferably in a pot that has drainage), wait a week before watering and see what happens.  You can also root the cuttings in the soilless mix but let them callous for at least a week before you do that.  Plant in slightly moistened mix and don't water again until you see new growth.  You can mist them.

This isn't the best time to try to start  a plant as they are going into dormancy buy you still have a little time left.

I hope you can save some of you plants.

Maureen