I would expect that with the rain we've had this summer (not sure where you're gardening), that most Sedums (most perennials in general) are flopping a little more than we're use to. Certainly, 'Purple Emperor' is known to flop a little more than others (hence its nickname 'Floppy Emperor').

My 'Xenox' is holding its own so far. It is beside 'Matrona', which is usually pretty good, but this year, has opened up in the middle quite a bit.

As for the "sun blisters", particularly on 'Black Jack', I would think this is likely powdery mildew.

In any case, stick with 'Xenox', as it's a great plant -- much better than 'Purple Emperor'.

do not fertilize.. them

do not improve the soil

and do not water them ..

treat them like a cactus.. and most years they will be glorious ....

increase water.. fert.. or good soil.. and they flop

ken

I have both 'Black Jack' and 'Purple Emperor'. I've found that when I cut them back about 6" when they're about 12" tall, they don't flop...or very little. It's a good way to get more plants that way too. You can either put the cut pieces in the soil and don't let them dry out for a few weeks, or put them in a glass of water until they get roots, then plant them in the ground. If you put them in the ground right away to grow, take off the bottom leaves. I just make sure I don't let the soil dry out until they get their roots growing good.
Btw, I'm not thrilled about 'Black Jack' either. I'm going to move it to an area where it'll just get morning sun, not the hot afternoon sun.

Kat

Yes, cut the 'Purple Emperor' back and you'll get nice, compact plants.

I fell in love with the color of 'Black Jack', but it got sun scald in our hot VA summer sun. The leaves were plain ugly and I was really disappointed. It also grew much taller than I wanted and posted about that here. People suggested I cut it back early in the spring and it wouldn't get as tall. I cut it back and IT WORKED!

One thing though, after I cut them back, each plant grew much wider, with more spread than the area called for. But if you want more plants you can always split them. As someone else said above, cut each stem back about six inches sometime in the spring when they're 12-18 inches high. And don't panic when you see how they look after pruning. Their appearance will improve nicely and will grow quite a bit shorter.

I noticed that some of the stems on 'Black Jack' were reverting back to the green variety, but decided that was perfectly fine since the dark leaves sunscald and get pretty ugly looking. There was no mildew, just sunscald.

Here's something interesting: Even though the 'Black Jacks' have mostly reverted to the green variety, the stems are red and flowers are darker pink than 'Autumn Joy'. The green leaves are also edged with red, so I very happy with the plant! Though green leaved, the plant definitely looks different than any other standard sedum. I'm quite happy with 'Black Jack' now that I learned how to handle it.

I guess I should count myself lucky. My Purple Emperor has never scalded, never splayed, never flopped, just looks great year after year. And I literally don't do anything other than spring clean up.

Here's a picture of it from July 19:

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Thank-you very much everyone for taking the time to share your experiences :)

I guess I will give the purple emperor another season before I pull them out. The rain was heavy this year, and although my autumn joy are not splaying at all, they are also not nearly as tall as the PE. So, I will trim the purple sedum next year when they reach 12" down to 6" and see if that helps :)

The color on them is so fantastic that if I could get them under control I would be very happy!