「花（はな）をもたせる」is an idiom.
花（flower）here figuratively means the honor(of success), credit as the one who did a good job, fame.
もたせる means to let someone have.
So, it becomes to give the honor/credit/fame to someone (in order to make a good reputation for him/her even when it's not really like that).
I think the example"部下（ぶか）に花をもたせる" alucky-san gave above is the most common situation to use the idiom.
In a company, when a boss and his assistant made some good achievement together, the boss often takes the credit. But if he says "Oh, no. It's my assistant who made it possible. I was just there. " The boss is「部下に花をもたせ」ています. What a good boss! lol
=something that is はなやかですand うつくしいですandりっぱです.