1/4 strength of whatever the recommended dosage is. So if it calls for a teaspoon a gallon, only use a 1/4 teaspoon to the gallon. You can't just go by the full dosage on the packages as to you may and probably will burn up your ladies.

Usually when I water, I give nutes one watering then just plain PH corrected water the next time I water. Also, remember when you transplant that you may not/won't need to give any nutes for a few weeks as your plants roots are being introduced to fresh soil (w/ nutes already in it) so they will use that first. Well unless of course your using a soil less mix as where you add your nutes yourself to the plants needs, but since your using MG you won't need to worry about that.