When to start feeding?

Hello all... this is something I've struggled with the last 4 grows... when to start feeding... I am growing three indicas and a sativa in Ocean Forest soil... They are just starting out veg. First plant today has 3 full sets of leaves...

I have always started too late in an effort to avoid burning them... but I have noticed today some purpliing in the stems...

Have I already waited too long?

Using Earth Juice Grow for veg...

sometimes the purple can mean a nute deficiancy but alot of times its just the genetics. i usually wait until about 3 weeks after it pops through the soil and then i only feed it 1/4 strength. if its a fert sensitive strain ill wait longer and it will tell me when to feed.

after like 4 weeks at 1/4 or not evn untill you flower