Hair grows at its natural rate. You dont have plants growing out your head so you cant just "feed" it. All products are scams just full of nutrients to make hair healthier...not to grow quicker. This is the reality of it.
You can't speed up the growth tremendously; some things will help a little. The best thing you can do is try to prevent breakage. Lay off the hot tools and get a good deep conditioner, use a wide-tooth comb rather than a brush, and stay out of the pool.