Choose your substitute based on the dish type and desired flavor match. Use kale or mustard greens for long braises, Swiss chard or spinach for baked dishes, and bok choy for soups and stir-fries.
Prepare the substitute as directed: strip tough ribs from kale and chard, blanch mustard greens briefly if a milder flavor is desired, and squeeze excess moisture from spinach before adding to baked dishes.
Apply the substitution ratio carefully. Use a 1:1 ratio for kale, mustard greens, Swiss chard, and bok choy. Use 2 cups of fresh spinach for every 1 cup of collard greens called for in the recipe.
Taste and adjust seasoning. Mustard greens add peppery heat so reduce added pepper if needed. Spinach and bok choy are mild, so a little extra salt or acid may be needed to match the depth of collard greens.