I'd say College is a good start if you can do it. It teaches you some things you may take years to come across in a shop, or maybe never come across at all. By going at least you will know, and also you will have your qualifications to proudly show off. Quite a few employers insist upon it, but all that said, you do gain alot more from shop based experience/training. Things happen there that college cannot ever begin to teach you.

It will ultimately give you a much much better understanding. I think its best to combine the both, it worked for me.
However many people i went to college with didn't have a day's placement, and its something our college sadly wasn't too good at enforcing, now they're walking around with floristry qualifications without a real grasp on what being a florist is actually like. Which is a huge shame.