“Why Do Bonsai Need Fertilizer?
Bonsai containers are a man-made environment. As such, they require you,
in order to maintain the health and development of your bonsai, to provide,
in addition to frequent watering, a regular dose of fertilizer to the soil or
growing medium.
What Type Of Fertilizer Should You Use?
Feed your bonsai with a balanced fertilizer, 20-20-20, at quarter strength,
every other week. The numbers 20-20-20 are the percentage, by weight, of
the N-P-K (nitrogen, phosphorus, and potassium) contained in that fertilizer.
These elements, in addition to minor or trace elements, are necessary for cell
division and enzyme processes that allow photosynthesis and the resulting
growth to take place.
What Does N-P-K Stand For & What Does It Do?
N – Nitrogen is responsible for the size and amount of new growth and, to
some extent, the green color of the leaves. Nitrogen is required for cell
division and, also, protein manufacturing. P – Phosphorus is also necessary
for cell division and is associated with good root growth and flowering. K –
Potassium activates cell enzymes and is related with overall healthy cell
activity.”
“Bonsai Fertilizer Notes

• Always water your bonsai thoroughly before fertilizing and never use
  fertilizer on a dry tree.
• Never fertilize a sick tree, as fertilizer is not medicine.
• When you have finished a bottle of fertilizer, it is a good idea to
  purchase a different brand, as they all contain different amounts of
  trace elements and minerals. Exposing your bonsai to different
  amounts of these important trace elements and minerals is very
  beneficial.
• If you are not sure how much fertilizer to use, follow the directions on
  the label and never use more than recommended.
• Fertilizer is a good thing, but too much is a bad thing.”

“That bonsai trees, as well as, other trees and plants, are capable of
absorbing synthetic nutrients through their foliage – oftentimes more readily
then through their roots. When foliar feeding, be sure to carefully follow all of
the manufacturers’ instructions and never foliar feed in direct sunlight, as
leaves can burn quickly. While applying synthetic nutrient, use a spray to mist
the foliage and be sure to check the undersides of the leaves, as there might
be ‘pests’ hiding. This is also an ideal time to check the wires and make sure
that they are not digging into the bark.”