Hi, Gabe:
Most herbs do not need a lot of fertilizer, but it might depend upon how old the soil was that you were transplanting into. If it is more than a year old, it might need a little (maybe 1/4 strength) fertilizer. Mint is pretty hardy, though, so make sure it is getting enough sun and water. I would also advise to tease the roots apart from your mint plants that came out of containers, just to make sure they are not rootbound. Mint tends to develop some serious roots, and likes to wind around the pot it's in. I usually end up cutting through the root mass while I'm starting new plants.
Thanks for joining us here on the herbs forum
