Open-pollinated. When farmer-breeder Brett Grohsgal passed out samples of his winter-hardy greens at two workshops at a PASA conference, this green mustard was the hands-down favorite. Grohsgal believes this mustard has the “best balance between sweet succulence and moderate pungency of any of the five I grow.” He called it Thick-Stem in honor of its enlarged midribs that give a heavier harvest for the farmer and better mass for the restaurant or home chef. Terrific for mesclun and an excellent cut-and-come-again performer with fast regrowth. Grohsgal has bred it for 100% freeze tolerance in Maryland. It survived our overwintering test in Maine. Needs good soil fertility, prefers clay or loam to sand, dislikes drought but can take wet.