Big Bloom is a low NPK plant food, and it's all natural/organic. Grow Big and Tiger Bloom are not, however, and you'd have to be more careful if you were going to use those as they are easier to over-do.
Depending on the mix you started in, and the size of the containers they are in, you might not have to start anything just yet. You might also just be able to transplant sooner than you'd have to give them anything, and then you could wait even longer. A couple teaspoons of Big Bloom isn't going to hurt, though. Just remember those other fertilizers are quite a bit stronger and are not like Big Bloom. The FF trio never made any sense to me.