k, ive got about a dozen seedlings of 4 various strains, all indica. They are all about 2 inches tall at almost a week old. the ? is, when do i start using nutrients?.. the last batch of seedlings i had i gave a weak dose of nute in their water and it burned them pretty good. oh yeah, they are in an organic mix that i made + perlite.
About 4 weeks after seedling emerges is what I do. The seed has enough nutrients to supply the seedling for about 4 weeks, water only for the first 4 weeks then go with 50% nute then move the strength up as the plant grows. This is the method I use and havent had a burn issue yet. Good Luck.
you can start 1/4 strength at around day 11 or so. after three alternating internodes is another safe time to start. the key is to start out at low doses and work your way up to full strength.