If your soil is low or deficent in P then any vegetable will benefit from it. P is used particularly in developing new growth, especially concentrating at the shoot and root tips, and if it is deficent or low when plants are young additions later will not overcome any P induced restrictions in growth at this stage. You could use it as a general broadcast fertiliser or, my preference, spot place a little around each transplant. It's low solubility in water also means that any new transplant, with their restricted root run, can suffer from a deficency if P is not in the immediate vicinity- this is why I would do spot placement. It goes further too!
