Wie gut muss ich mich mit Blumen auskennen, um eine Lehre zur Floristin anfangen zu können?

You should have a keen interest in plants, nature and, of course, flowers, but you are not expected to have extensive knowledge of floristry when you start an apprenticeship as a florist with an Federal VET Certificate or Federal VET Diploma. Learning everything you need for this profession is the task of the apprenticeship, for which you have two or three years. So if you know very little about flowers or plants before you start your apprenticeship, that's not a bad thing, because after all, that's why you're doing the apprenticeship.