Remember to uncheck the 'Use Fresh Ingredients' box at the top left of the crafting menu if you do not want to use your stored flowers. If the flowers themselves are decent quality it helps to increase the quality of the final product, while also saving you from having to buy them before you can craft the arrangement (this is done automatically).
With each arrangement, you have the option of using fresh flowers. You'll be losing money for the first few levels unless you have fresh flowers. Skill books are available as well and it's certainly encouraged here. Simply purchase the Violets are Blue Flower Arranging Table from Study > Hobbies and Skills in Sort by Room (Buy Mode). You can start floral arranging without taking the gardening career, though you'll certainly get some extra money by working at home as a florist after getting through the early gardening career levels. You'll automatically buy any missing flowers, getting a discount if you have even some of the required flowers. Check out my many mods here! Uncheck 'Use Fresh Ingredients' if you'd like to preserve your flowers. Explore My Mods! Color Picker for Builders, Seasons Tuner, Dine Out Reloaded and a Gameplay Overhaul! Like other modders, I've been working to make The Sims 4 a better game.