From what i understand. (and I have to tell you I don't understand a whole lot) The plants will not use fertilizers in the water column when they are freshly planted. They need to become established in your tank first. While they are doing this they only use stored nutrients. Therfore dosing ferts in a newly planted tank will only attribute to growing algae instead of your plants.
Anybody with a little more experience feel free to chime in!