maybe never.

the trick here with these plants is to add ONLY what is needed WHEN its needed. Dependent upon your dirt, you may not need to add any ever. You have to wait for the tell tale signs of need.

Either way, do not ever feed your plants anything other than gentle organic nitrogen as long as they are in the veg stage.

As for seedling stage, never give them anything. Those little green pods that first emerged from seed and now sits at the base of the stem...those feed the plants for the first 14-21 days. NEVER feed while those are plump or have some color in them.

Sounds like you should really do some serious reading. You are asking a question about something that has destroyed more plants than any spider mites infestations have combined.

GOod lucK