A few of us have tried Agave spp. here in the Minneapolis, Minnesota area. With the exception of
Manfreda virginiana, none have been successful. Common among us is the fact that even though the crown dies over winter, usually new sprouts from roots emerge in mid summer. Usually these sprouts do not gain enough energy by summer's end to survive another winter. I am not sure what the actual cause of decline is. But I can say that plants look okay until early spring, and long after they thaw. This is
Agave parryi, sourced from above Flagstaff, AZ, probably the most cold hardy strain. First pic take April 3, 2013. "Something" seems not quite right, but it is too early to declare fatal damage. Second pic, April 27.