Permaculture nurseries in winter

Hi all,

We're working on starting a permaculture nursery in Reno, Nv. The climate is high desert, and we get temps as low as -14 F historically.

Does anyone have references, resources, or suggestions for keeping potted plants alive and thriving through the cold season without bringing them indoors?

Currently we're considering thermal mass, sand and straw insulation, and a shade cloth covering over the top to trap radiated heat.

thanks in advance for any info.
Neil Bertrando