Select the substitute based on the recipe type: daikon or red radish for raw dishes, turnip or kohlrabi for cooked dishes.
Prepare the substitute by peeling, dicing, or slicing to match watermelon radish's size and texture.
Apply the substitution ratio of 1:1 by volume or weight as indicated; for the DIY blend, combine equal parts daikon and red radish.
Taste and adjust: soak red radish slices in ice water to mellow sharpness or use seasoning to balance flavor as needed.
In cooked dishes, cook turnip or kohlrabi gently to maintain texture, avoiding overcooking to prevent softness.