Hello. I have a bulbispermum and a scabrum that I wintered over, planted quite deep--base of the bulb about 14" below ground surface. Sited about 20" away from the foundation of the house. Tip of the bulb was below the surface. No mulch. We had about three zero F° days last year.. I don't know how they would do in a more normal winter e.g, at 15-20 °F for a week or so. I plan to find out. Tony Avent's criteria don't work for me here in 5a but they help. Jim Waddick's criteria work better in Glenview, (Chicago suburb).