when to use fertz?

I assume you are growing in dirt. If you use a good 3 part nute system (General Hydroponics has decent ferts) there will be a chart with indication as to what proportions of nutes you gotta use throughout the plants life cycle. I grow aero so I dont know if its as effective, but I always give 15% less nutes than I calculate, this way its nearly impossible to get nute burn (unless your math is all fucked up). Also many many people are against MG soil, maybe go down to your local hydro shop and ask around for any other soils they will recomend. Hope this helps.

 

4th to 5th week probly depends what kind of soil your using.

for MG I would say 1/3 the rocomended dosage for that suff its kinda strong.

Ive used it outdoors and it worked well, but havnt used it indoors yet.

I might give my plants 1 shot of that in late veg, for the all around metals and nutes its got in it.