Bloom are originally released on June 19th, 2012 with Bloom Garden. When you harvest your Bloom Garden you have a chance to find Mystery Bulb that with Flower Food can be grown up in Full Bloom.
Single Blooms are available as limited edition items in Market during Event or during different FarmVille features - Quests, Countdowns, Voting Buildings... If they are placed on farm they can also be harvested but if you forget it, they can wither! You will need then Flower Food to get them to life. In Bloom Garden they can be harvested every day and can not wither.
If you get Mystery Bulb after harvesting Bloom Garden it will grown in Full Bloom version of parent inside Bloom Garden. Full Blooms never wither and can also be stored inside Bloom Garden.