To make your Garden feel a little more unique you can decorate using decorations from the decoration shop! You will need to have rebuilt the decoration shop first. Decorations are purchased using Decoration Tokens, which can be earned from the Community Barter Board or purchased via in app purchase in the shop.
To place decorations: tap on the planting icon (trowel/shovel with a flower) to open the Seedling menu then at the top of this area there are two tabs, one of which looks like a stone carving, and if you tap the other tab you will see any decorations you have access to. Decorations are placed much like plants and you simply drag and drop the item from your Decoration Menu into your Garden. Items can be moved around in the Garden when you have this menu open, so that you can alter the look of your Garden! To put Decorations away simply drag them back into the Decoration Menu.