September 2013 issue of the Cornell Flower Bulb Research Program Research Newsletter:
Eucomis planted in 2012 overwintered at Bluegrass Lane research facility. Since we did not anticipate any survival, we really did not keep accurate records on the number of plants used, etc. But it is clear from the plots and photos that the plants were substantially hardy that winter, and did not suffer any extensive winter damage. Trust us, we do not have a lock on global warming in Ithaca, but this just points out that plants can’t read, and in the right place (well drained soil being essential as winter wetness is usually to blame for marginally hardy plants failing in the winter), many plants will do better than expected. For the record, Ithaca previously was in the cold end of zone 5 (zone 5a), and now resides in zone 5b with the winter hardiness revision from 2012.
Read the whole article. Starts on page 5.