Question

either way

I'd streamline it by saying-
They create a healthy environment for trees and flowers.

thanks all~

Actually, you don't need the definite article at all with "trees and flowers."

They create a healthy environment for the growth of trees and flowers.

Using "the trees and flowers" might seem to imply that you have already mentioned trees and flowers, and that you mean those trees and flowers and no others.

great explanation! thanks!