Choose the substitute based on your recipe's cooking method, such as kale or mustard greens for long braises, baby spinach for raw dishes.
Prepare by stripping tough stems from kale, mustard greens, and turnip greens; chop Swiss chard stems to add first if sautéing.
Use a 1:1 ratio by weight or volume to replace collards with the chosen green.
If cooking with mustard greens, add them early to reduce sharpness; avoid cooking baby spinach to preserve texture.
Taste and check texture during cooking to ensure the substitute meets desired bitterness and firmness.