I'm not sure which board to post this question on, but here goes:

Last spring I planted three Yarrow plants (Achillea Summer Wine). They've done well and I took care this spring to keep them from taking over. They have bloomed once, bright purple, but now the blooms are spent and have turned into a dirty sort of purple color. Am I supposed to cut them back? Also, the stems are long, about 14" or so, but they just fall over onto the ground. Is this right?

I appreciate any thoughts you might have (even if it includes posting this on a more appropriate board.)

Thanks!

Shannon