Realizing this is an old posting, but having been a private-client florist for many years, just wanted to throw my 2 cents in here.
I always tell my clients who want to learn the bare basics to start with Martha Stewart. Her books on weddings & her magazine offer the most concise and user-friendly infomation on the open market. The information she and her extensive staff offers the newbie to floral design a realistic success rate.
If you are after a more "florist level" professional learning experience, with the idea to go "pro" yourself, the best learning is to be had by DOING.
Find the local Professional Florist or Event Planner whose work you most admire and ask to be a floral assistant....part-time work for these professionals is the best training in the world.
Most professionals started this way and your skill-set will exponentially increase by immersing yourself in this environment. (i.e. - all the books, videos and college classes in the world won't give you real-world experience...and TRUST ME, you DO NOT want to 'experiment' on someone's wedding day or private event.)
The most successful florists I know can think on their feet and know - through experience - how to handle wedding day/event day mishaps or challenges.
If you do choose to apprentice or take a part time position, you will learn things the books and videos simply don't cover well - such as CURRENT real-world pricing, best practices in customer services, the newest design techniques/trends and tools of the trade/vocabulary.
Plus, your personal portfolio will grow with each job you do.
If you can learn all this valuable information from an experienced professional, 'a la some form of apprenticeship, you will gain confidence, experience with a vast array of floral materials of ALL types and your work end up at a FAR higher level of professionalism in the long term.
Hope this helps.
Good Luck!