How often do they need fed?

Say I'm using a 20-10-10 or a 30-15-15 plant food for the vegetative stage. How often do you feed them? Everytime you water? Or do you feed them like once every here and there? I'm new to this. Thanks.

I feed every 2 waterings..i water every 3 days or so...

You may not need to feed them at all during veg, depending on which soil you use, and whether you follow a good potting up routine.

you have to test to find out . i use fox farm fertilizers every time i water. i dont know if i would do that with a store bought fert though probably just follow the instructons on the box or bag. if you buy the right soil and the right fert you can feed every time you water