Dear Jim et al:
Comparatively, there are not many truly hardy
bulbous in South America. You have several Tristagmas, Hyeronimiellas,
Phycellas, Alstroemeria both described and undescribed, Solarias,
Rhodophiala andicola, R. elwesii, R. araucana. But, all of these spend their
winter dormancy under snow, which of course means a lot milder temperatures
than your freezing soils.
I do not think it is a good idea to leave your
Hesperoxiphion outdoors for the winter unless you have heaps to discard. A
cold greenhouse would be tolerable for the plants but they do not experience
freezing grounds in the wild.
Regards
Alberto