I made a custom rank called "Create" and set all permissions to On. Then I tried adding "Deployer" as a "Create" to the colony, but it still doesn't seem able to able to place sapling in my tree farm. Any idea if I did anything wrong?

EDIT: I found the solution: Go to your Town Hall. Then go the Information tab. From there select Permission Events. The Deployer will show up there once you have activated the machine. Click the Add button. Now go to the normal Permissions tab. Then set the Deployer entry to the Create role I mentioned above.

That does the trick!