Broccoli can be picked when the florets are mature, but before they actually bloom. They should be about the same size as the ones in the store. While the heads are not going to be the same size unless you are really lucky, they will taste far better. Soak them for about 10 minutes in a salt water solution to kill any little critters and then rinse with cool water to get the salt taste out. I have already picked my first crop. Do not take the plants out as they will produce side shoots that while not as big as the first crop are just as good.