If you got regular sweet peas...not dwarf ones...they grow like regular edible peas...on long vines. You can train them to grow up onto a trellis,..or let them crawl all over the compost pile. Let them crawl onto the wire around the compost piles. It's a good way to hide those! They will grab onto anything to grow upwards sooner or later. I think that they look better upright, so that you can see the blooms and smell them.
I can't grow them here in south Fla. it is to hot. I miss them so much. I grew them up in my home in Conn. and they covered a fence that I had my tomatos growing next to,..to attract bees and for the color.
So you can do either. But they will try to climb no matter what you do. Enjoy them!!