I have played with the terrain and it's not bad at all. However maybe the gardening feature should be linked to the terrain. Then the user could be able to make an array of foliage or trees to randomly select when gardening.

The reason I suggested having the gardening feature under the terrain modifier is so it will know to automatically snap to the surface of the terrain versus having to turn on terrain snapping.

Then have a custom option as well where the user could place props through the landscape if they was trying to get a rumble and trash scattered the terrain.