I went around in a few circles trying to find the label for Miracle Gro Quick Start Transplant fertilizer, 4-12-4 which I assume is what you used. I couldn't find it but from the web site it doesn't say for use in container plants. I'm thinking with that formulation it is for transplants into the garden when the soil is cool (otherwise the P doesn't need to be that high). From the MSDS the ingredients are ammonium phosphate, potassium phosphate and urea. In the proportions and the dilution you used it probably that isn't particularly salty but it's not necessary to go that high with P in containers. The main concern with transplants is getting enough water and a too salty fertilizer can interfere with that. Fertilizer is not an urgent need for transplants, especially if their roots are damaged in the process, and can wait until they're growing again, to be on the safe side.
