Mustard greens are a great winter garden plant . I've harvested them with snow on them and they keep growing .A novice gardener I remember posting a long time ago asking " how long can you store seeds " ? A few days ago I planted mustard greens , using seeds that I bought in 2017 . They are now up and apparently got a very good germination rate . Those seeds I keep in a freezer . All my other seeds I keep in a shoe box at whatever temperature my house is . I don't expect them to last as long as the mustard green seeds but perhaps lasting around three years . However I prefer using one year old seeds that I collect annually . --- Think cooler weather seed for the potential Nuclear Winter ahead . Estimations vary but have seen around 30 degrees cooler than normal floated .