This completes the mix for maples and most plants. The purchase of a good commercially available potting mix simplifies the process, and is sure to get you off to a good start. Fertilizers are chosen for the individual species of tree grown, but in general the rule is a little goes a long way. We are not trying to encourage rapid growth. On the contrary, we want our trees to be healthy and happy, but it is our goal to keep growth slow, so the use of nitrogen is watched carefully, and is very limited except in the spring when new growth is being encouraged.
Many folks find fish emulsion to be the perfect solution.
It is a complete food, is low in nitrogen, and is easily used. Care should be taken to apply slow-release formulas early enough in the season to prevent pushing soft growth in the fall that can invite damage from an early frost. For some reason many of us are intimidated by the idea of root pruning. It is really not difficult, and since only the new root tips are able to uptake water and nutrition and the old roots take up valuable space needed for water and air in the container, root pruning is essential to the long term health of the tree. The pruning of the roots rejuvenates the tree, and should be done every 2 to 5 years on older trees, depending on species.