He picked a nice pinwheel to finish the decoration.
First we picked up a fence at Home Depot. Then I let the boy pick whatever color of spray paint he wanted and we decorated the fence. (Mom did the painting part)
I then had him pick out whatever flowers he wanted in his garden. This time of year you can get loads of sturdy flowers for $1 each. You don't need a lot, since you are just making a tiny garden.
I let him pick out his own watering can at the store. I wanted it to be something he picked and small enough for him to handle, because my plan is to have him water his plants every day as part of our routine.