well- pachy spreads two ways. one is by growing until it is so tall that it flops over, growing vertically again, and rooting where it lies. it also sends underground runners out- which need somewhere to come UP, yes?

if you have many weeds, treating with a pre-emergent

www.GardensAlive.com

http://www.google.com/search?hl=en&lr=&q=corn+gluten+meal+&btnG=Search

may be a better thing than just round-up'ing the bed four days before you plant.

I've seen people use burlap to hold them upright through the first year (cut a slit big enough for the dibble/hole digger) but that degrades inconspicuously without hurting anything.