Saplings are baby trees that are sold in small pots. From the day that they are planted in your village, it takes three days to fully grow. Saplings can be bought from Tom Nook's Store in all of the Animal Crossing games except New Leaf, where they can be bought at the Gardening Store. Saplings cost 80 Bells each. Oak Saplings are sometimes just called Saplings in game and grow into oak trees. They look just like an empty fruit tree, except in New Leaf where they have a slightly different color pattern. Cedar Saplings grow into taller trees that resemble fir or pine trees. During the month of December, about half of these trees will be decorated with holiday lights for Toy Day.
When you first start the game in Animal Crossing, Wild World, and City Folk, one of your first jobs at Tom Nook's Store is to plant saplings and flowers around his store to make the shopping experience for customers better, though in reality you can plant them anywhere in town, or even keep them. At the end of the New Leaf tutorial, Isabelle will give you three non-native fruit which can also be planted (using a shovel, however) to grow fruit trees.
Saplings cannot be planted in any space that is covered in cement, bricks, patterns, or directly in front of the door to any building. Saplings can be planted in any other full square, but they will not successfully grow if directly next to a building, river, rock, bridge, cliff, ocean, or another tree. In addition, in all games exist certain spaces in which a sapling will never grow into a tree. If a sapling ever dies in a space when it would be acceptable to grow, all saplings will always die in that specific spot.
In addition to improving asthetics and town ratings, in New Leaf, they play an important role in obtaining the Golden Axe. After the player has purchased 50 Cedar and/or Oak saplings, Leif will thank the player for their dedication to gardening with the tool.