I live in east Texas and this winter it got down to 7 degrees below zero for one night and was very cold and snowy for a week.It may be a trend.How can I build a cold frame to cope with this?I want to grow Gynura Procumbens or longevity spinach all through the winter.
"Imagination is more valuable than knowledge".Einstein
Maybe try Four-Season Harvest : How to Harvest Fresh, Organic Vegetables from Your Home Garden All Year Long by Eliot Coleman.
He also has The Winter Harvest Handbook.