I have never heard of using dry powdered milk on tomatoes. I do know that adding calcium to the soil will help prevent blossom end rot and perhaps this is how the powdered milk advice came about. I just use a complete fertilizer with micro nutrients like Osmocote on my tomatoes, and never have to worry about a lack of calcium. If you do try powdered milk on your plants watch for lots of cats after a rain storm! Keep growing, Marianne Binetti