If you play through the Chao Adventure 2, the VMU game, you will find seeds at the end of some of the quests. These seeds can be taken to the Chao garden and produce rare fruits. In order to plant these seeds, you need to first win the shovel and watering can in the beginner Chao races. As soon as you have won these, take the seed out of the VMU and give it to one of your Chao. The Chao will take it, plant it, do a little dance and a little weed you appear. Eventually, it will grow into a tree that you can use to help improve your Chao stats.