whats good seedling stage ends at the end of there 3rd week from sprouting once the plant begins developing secondary growth and its obsorbed all its initial nutrients from the seed and its ready to feed from nutz and what not its now in vegetative growth im growing from cfls veg and flower bu i'd recomend switching around the 4th week or jus introduce the light along with the cfls gradually or jus switch them right off mh lights are great for veging so they should take jus fine after the 3rd week