This is a great website, tells you 10 things to do with leftover composite deck boards
We built raised beds for flowers with some that were donated to us.
Yes this site is good for ideas - basically use the boards as if they were timber!
I used some of mine to make a stand for 4 Water Buts alongside my house, wonderful because they will not rot!
Planters and seats or tables for the patio
my husband makes long planters out of them - perfect for spring flowers