I've grown all manner of hardy evergreen euphorbias for years and always remove the old flower stalk at the base of the plant (or as close to it as possible). These will never produce flowers again but can sprout some new shoots along their length that can become flowering stems down the road. However, a full or more complete removal results in a stockier and more robust plant. By the time you remove the old flower stems, the plant has produced new basal growth that will become the next season's flower stems.

The only exception I'd make for this is with Euphorbia amygdaloides var. robbiea, or Mrs Robbs Bonnet, which is a spreading, suckering variety ideally suited to dry shade. Pruning these individually takes more effort than I'd care to spend and since they are suckering anyway, a stockier plant is not really of any additional value.

Thanks gardengal, that's exactly what I need to know. I would like to keep this plant in a rather limited space, so serious pruning makes sense.
Jan

Ruby Glow should stay put without worry. It is not the most robust euphorb I've grown (IME, the darker the foliage, the less hardy the plant) and doesn't seem to produce any stoloniferous growth. Robbiea, on the otherhand, spreads aggressively via stolons, especially in better soil and plenty of irrigation and is often sold as an evergreen groundcover for difficult situations. There is some thought that robbiea is a distinct species of its own, since its growth habit is markedly different from other amygdaloides selections.

Hey GardenGal! I live in zone 7b and have some ruby glow and ascot rainbow in a container in full sun on my roofdeck. I recently pruned my euphorbias down to the base, foliage and all, because I thought that was the right move. I am reading now that they are spring bloomers. Did I just totally mess my plants up for this spring? I cant find any pruning advice that isn't directly about spent flowers online. Any advice?

I think you probably did......sorry. It is bloom season for both of those right now in my location.

Pruning advice for hardy euphorbias - or what I prefer to call "clean up advice" - is pretty generalized, just due to the diversity of species and hybrids and their variety of growth habits. But the advice regarding pruning spent flowers is pretty much on the mark. That's really all the pruning most require. Most will only flower once from a single stem. When those flowering bracts finally go over....and they can last and look good a long time......you cut those stems back to the base. That's it....nothing else required. New foliage is being produced at this same time and it will grow into next season's flowering stems.

It is really just severe deadheading rather than pruning :-)