when do i add ferts

Depends on your medium. If you're in soil that has nutes like FoxFarm Ocean, you should wait at least 2 weeks unless you use bat guano or worm casting, in which case after the seedlings first true leaves are half and inch wide each. Organic ferts are less prone to burn a plant.

 

I'm doing my 1st grow & getting great results from using 4 gals. Fox Farm Ocean blend soil,2 gals organic soil w/ no nutes, 2 gals plain old potting soil,2 gals good compost blended w/ a med bag of perlite, 3-4 handfuls of greensand, handful of blood meal, 2 handfuls of bone meal mixed well (will fill 5 - 3 gal containers) & then bottom & top dressing the plants w/ 1/4 cup of worm castings & 1TBSP of Indonesian bat guano.

I almost drowned my (4) White Widows (rockwool is not for soil planting IMHO) at 2 weeks & now at 5 weeks they are about 8" tall & about that wide around & they just got their 1st nutes last week. For nutes I use in 1 gal of water in veg stage - 1TBSP of Peruvian Seabird guano, 2-3 drops of superthrive,1/4 cup Seaweed magic & 1TSP of molasses. When they go to flower stage the only thing I'll change is the guano from seabird to bat & I foliar spray once a week w/1/4 nute solution to 1 gal of water & fine mist them & twice a week w/ plain selzter water for co2.

My 2nd crop of ' White Castle' was started on May2nd & 4 out of 5 popped up & have 1st set of true leaves already & are about 2" tall & I'm using CFLs!

Don't know if that helps but w/ good organic mix you don't need alot of nutes (my outdoor 'legal' garden does fine w/ it & produces tons of flowers & vegies & they are lucky to get nutes twice a season after the top dressing of worm castings & guano when planted & I had 1 cayeene pepper plant produce over 700 - 5-7" peppers in 1 season & my vine plants get as thick as your wrist at the base so I'm hooked on the organic way totally - PH stays almost perfect & plants are healthy!