Are mustard greens a good winter cover crop?
Winter Cover Crop
Certified GKH Gardening Expert
These quick-growing plants can be grown for winter greens if you live in an area where temps do not get much below 45-50 F. Protective devices like cold frames and row covers will help them withstand cooler temperatures.
Here is more info on growing them: https://www.gardeningknowhow.com/edible/vegetables/greens/growing-mustard-greens.htm