Is there a way to change the pivot point of a combined mesh?

So I had this issue where I would import a mesh I made, in this case a plant, but it would be imported in 3 different parts instead of just being 1, I merged the mesh, but now even if I try to use it for foliage half the plant is buried on the ground since the pivot seems to be in the middle, is there a way to move this pivot to the bottom of the plant or do I just have to manually move up the plants after painting them in with the foliage tool?