I also grow some Euphorbias, and what I learned with them, to root a cutting, I make sure cutting is callused then stick it not too deep in gritty soil and in part shade area. It will then acclimate to set-up and wait till temps are warm enough. So the timing you do the rooting is important. Warm will be when daytime temps have reached 70 to 85F and overnights are above 50F.
When temps go extremely high, like 95F and higher, as with most cuttings, it waits. But once it is rooted, it loves watering here, since our area is just so dry, and can take our full sun by then.
I only have them in small containers, since I have to move them indoors during our wet winters. During winter, I bring them indoors by our south facing window and kept dry.
