Can these hybridize? I have them potted next to eachother and was wondering if they will hybridize being one is cold hardy and the other is not?
Swamp Milkweed x Tropical Milkweed?
I dont think the zone tendencies are why the milkweeds would cross or not. It will be the blooming times that could cause it. Shrug. Pinch blooms on one plant or the other so only one blooms at a time if it worries you. I am gonna go do some research tho.
http://www.gardenswithwings.com/facts-info/2009NL/MilkweedPlants it was handy- hope it helps