A spirit seedling (w) is a result of watering a spirit seedling. After a few seconds, it will mature into a spirit sapling, which can then be planted into a spirit tree patch with level 83 Farming. In order to plant a second spirit tree, level 91 Farming is required and for a third (Unlimited amount of trees), 99 Farming is needed. The seedling will mature while banked, there is no need to hold it in your inventory.