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When the roots start to thicken and turn brown, separate your new tree by cutting it off below the new roots. Partially fill the container with good quality topsoil (a good mix consists of about 80 percent bark and 20 percent peat, as this tends to promote fine fibrous feeder roots and gives good drainage. Unwrap the plastic and without disturbing the roots, plant your new tree, adding additional soil as needed to firmly set the tree in place. The addition of sphagnum moss is helpful in hard water areas. A stake will help to keep the tree from moving; while it is establishing itself, any movement can damage its delicate roots. Find a suitable outdoor area to keep your bonsai, such as a porch, garden bed area or patio. Bonsai are not meant to be indoor plants; if brought indoors, only keep them inside for a one to two days before returning them outdoors again; only bring them in when in leaf, or only for an hour during winter.  Keep the bonsai maple tree sheltered for the first few years. Don't leave it outside where frost can get to it for the first 2 to 3 years, as this can kill it. Avoid placing the plant anywhere windy and do not let it sit in direct sunlight for the whole day.  Feed a balanced feed after the buds form until late summer. During winter, feed with a low- or zero-nitrogen feed.  Never let a bonsai tree dry out. It needs to be kept slightly moist at all times. Wherever possible, use rainwater rather than tap water; it's healthier for the tree. Regular spraying with water is helpful for healthy growth. Learn to "style" the tree as it gets established. This is where you learn to reproduce what nature normally does, to give the tree the look of a real tree. It consists of careful pruning and wiring. Getting this aspect right can take a lot of practice but that's all part of the fun of growing your own bonsai.

Summary:
Separate the tree. Place small pebbles for drainage in the bottom of a pot. Insert a small stake. Enjoy your new tree!