When to start adding nutrients

Fertilizing usually starts when the first set of leaves has fully matured (second set starts growing) and with about 1/5-1/4 of the recommended fertilizer dosage (always better off using less since deficiencies are less stressful to your plants than toxicities!), as the plant matures or show deficiencies you add more fertilizer. Listen to your plant and pay attention to the leaves! they are the best indication for fertilizing needs!. Hope this helps! Good luck and happy growing :)