Well, if it survives in Michigan that is pretty darn hardy for a plant with tropical affinities. I ordered seeds from someone in Oklahoma. I dunno if Oklahoma gets down to 20 below but it might even though it is so far south, as a result of the flat terrain that does not stop cold fronts. "Nothing between you and the north pole but a barbed wire fence" (old saying).
Lilya, have you tried them?
Soapberries could be the secret weapon in my war on phthalates. Should make tolerably good shampoo.