I have had a tall sedum ('Red Cauli') for a couple of years. Instead of staying in a nice clump form like 'Autumn Joy', as it grows it flops and takes up too much space. Right now it is about 18" tall and just starting to form buds. If I pinch each stem back, can I keep it looking nice and will it form new buds? I guess I want it to look like Autumn Joy but with different color flowers

Do you water it? If you can, try not watering it, or water it much less. This may be a problem if you are in a wetter climate than me.
Although it won't ever be as straight up as Autumn Joy. When it gets less water the stems don't flop, but they do curl outwards.
This is mine with minimal water and in a very dry climate:

And full sun should help also. Are you in NM? If so full sun might be a bit harsh.

My subject should have been: Can tall sedum be cut back to prevent flopping? [Not "untitled"] Last year when 'Red Cauli' flopped so badly, we had very little rain, and it was in a bed with daylilies, which should have been watered, but were not. So I don't think over-watering was the problem. I live in Minnesota. I think I'll try cutting back a few stems and see if they recover and get new buds.

They'll get new buds if you cut them back. Mine was devastated by hail which broke off all the stems and it sent up side shoots off the broken stems. In the end I don't think it was any shorter, but the blooms were smaller.

Your thread is not titled.

By the way, I just realized you are new to ATP. So a big to you. And so glad you found your way here.

I've never had to cut any of my tall sedum back, but I know that you can pinch them back when plants are about 8" tall, no later than mid
June. Pinch back to 4–6", leaving 2–3 nodes to produce lateral branching.
It will produce smaller blooms, the more blooms the smaller they will be.

Hope this helps.

Yes, to ATP!! and have fun!

Great to have you here!! Let us know how your experiment turns out.

I cut mine back all the time. I cut mine in staggered lengths. Taller in the back, shorter in the front but, leaving at least 2 -3 nodes like Lynn said. Then I root the cuttings. I like that look rather than a round ballish shape.

Great way to increase you sedum plants.