The general premise is that all bonsai fertilizers must contain the three primary elements of nitrogen (N), phosphorous (P) and potassium (K). Learning what source is best for your bonsai growing conditions is essential.
Organic or Inorganic?
There are two sources for bonsai fertilizer – organic and inorganic. Organic fertilizers are less processed, are easier to break down and to be absorbed, and haven’t been synthesized or altered in their basic makeup. Inorganic fertilizers provide control over nutrient levels, are soluble, and have been refined to increase potency.
You fertilize to replenish the nutrients in your bonsai potting medium, with plants absorbing all nutrients as inorganic ions. Inorganic fertilizers increase biological activity, with the microorganisms helping your bonsai tree to convert nutrients into food over time. Organic fertilizers dissolve into ions that are more quickly available.
A good potting mixture cannot hold fertilizer for long because of the porosity and the relatively small amount. Therefore, it’s necessary to balance the frequency and source of your fertilizer. Organic bonsai fertilizers decompose gradually, releasing nutrients as they retain more moisture than inorganic fertilizer.
In addition, add your growing conditions and specific species requirements into the formula mix for fertilizing. For example, seed and fruit-bearing trees need more nitrogen, while more phosphorous is needed when blooming trees are in bloom. If your bonsai is in full growth or dormancy, immature or mature, newly re-potted or any number of other considerations also alters your fertilizing formula.
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Organic fertilizers are generally safer because they will not burn roots as easily and are not as likely to leach from you bonsai soil. However, the release of nutrients is less predictable and many are not balanced. In addition, since all are derived from plant or animal matter, using some bonsai organic fertilizers inside can, literally, cause quite a stink.
Inorganic fertilizers bring with them a more easily-identified balance of nutrients, with faster release and specific potency. They have little or no odor, too.
Going organic with bonsai fertilizers, with a little inorganic help, can produce full foliage, fine flowers and fruit, and essential nutrients.