You can decorate your farm with various objects: flowers, sculptures, garden furniture and fences. Some of them can be bought for Green Bucks, while others, especially rare, will require Gold Coins.
These decorations are not purely cosmetic. When placing new items at your farm, you also increase the number of your Prosperity points and get some experience points.
The higher your level, the more items are available to you.
Gnome with Lantern