It’s best practice to wait to wash collard greens till you are ready to cook with them. If you wash them before, the excess moisture can cause them to spoil quickly. When you bring home your collard greens, store your unwashed leaves in lightly moistened paper towels and place them in a ziploc bag till you’re ready to use. After washing your greens, you should aim to use your refrigerated collard greens within one week.
You can also freeze collard greens to store them for longer. If you wish to store frozen collard greens, you first need to blanch them. Blanching refers to quickly cooking a vegetable for a few minutes and then immediately placing it in ice water to stop the cooking. This will give you the best texture and product for when you use your frozen collards. After blanching, let your collards cool completely before placing them in a ziploc bag and storing them in the freezer. Frozen collard greens are good for up to one year.