Are you feeding?

I'd keep them lean if they are flopping.

I keep mine trimmed up (kind of flat-topped) until July 4. Just like mums.

It seems to make them bushier and less inclined to flop around.

Typically they will flop with too rich soil or too much water. And you can always do a Chelsea chop in late spring to keep them bushier and more compact.

over watered.. and over fertilized ... and the soil is just to good ..

when i moved to all sand.. and never watered nor fertd my sedum.. they grew just perfectly.. lol ..

they werent quite as big.. but who needs a big plant that flops .. eh??

ken

I do not fertilize... in general. Watering too much? Maybe. But I don't irrigate that particular spot. In fact it's quite dry. Maybe the soil is richer than I realize.

What's a "Chelsea chop"?

Can you do this with many other perennials?

Yes, lots of later blooming perennials like phlox, asters, solidago, helenium, ecinacea, achillea, perennial sunflowers can benefit.