[BKKG]

The search button could have answered all of these questions, as well as each and every grow guide that I've ever come across. But regardless...

For veg, you just want ferts with more N thank P or K. The Miracle Gro I use is 24-8-16. For flowering, you want a bit more P. My flowering fertilizer is 10-15-10. The time to switch between them is when you switch from vegging your plants to flowering them.

The veg stage is generally considered to be the period after your plant grows its second set of true leaves, and before you begin to flower it. It'll be in veg until you switch its lights over to a 12/12 cycle. Once it's mature enough (usually a month at least, but you can veg as long as you want) and you've switched to 12/12, in about a week (give or take) your plant will begin to show its sex characteristics, which is generally when people say that the flowering phase has begun.

Also, make sure that you use a low concentration of ferts when you mix with water. Some MJ plants are very hardy, and others can't stand extra nutrients and get nute burn.