I had Komatsuna seedlings in the cold frame before the Beast from the East arrived. They were two weeks old and about 75% of the seedlings survived the Beast (-9°C at its coldest here, and icy wind drying out the soil) without additional protection (like fleece or straw). I actually wanted them to die and just sow again after the Beast, but won’t be necessary 🙂
Also lettuce seedlings (Winter Gem) survived.