Hi Laura, I’m not knowledgeable about expanding in Idaho, but we do live in a similar USDA hardiness zone. Two varieties of milkweed that catch the attention of lots of monarch exercise are swamp milkweed (asclepias incarnata) and tropical milkweed (asclepias curassavica) since they are used as each host crops http://cannabis05050.look4blog.com/11833268/about-buy-weed-seeds-arkansas