The good news is that this key will help you complete two different quests, and give you a way to enter the Lower City of Baldur's Gate. That said, here's where to use the Flower Key in Baldur's ...

With Level Keypad, users can now add handy key codes to the list. The Level Keypad can be mounted anywhere within 30 feet of your lock, and mounting it is easy using the included mounting hardware.