Bumblebees need flowers throughout the spring and summer (March-Sept), and these need to be the right kinds of flowers. Exotic or highly cultivated garden flowers aren't very good as they either produce no pollen and nectar, or keep it hidden away from the bees. Most annual bedding plants (for example Pelargoniums, Begonias and Busy Lizzies) have no nectar in the flowers for bees or other wildlife - you might as well plant plastic flowers in your garden.
The Honey Bee Colony: The hive consists of three castes of bees. Queen• Fertile female responsible for the total population ~ Worker• Sterile female – does the work of the hive ~ Drone• Fertile male – exists to mate with queen