End of growing season for fall crops
How long can you harvest broccoli raab and Swiss chard after a hard frost even when leaves are still green?
Howard County Maryland
You can harvest until the plants do not look edible. You can cover the plants with row cover for frost protection and to extend the season. Swiss chard can overwinter but usually looks ratty in the spring. http://extension.umd.edu/hgic/floating-row-cover