I wrote this mail to a friend and thought this could interest many others. The friend had asked why I would feed a lot more than other folks.
Normal feed mixtures are for normal plants. Normal plants grow in soil which already has nutrients. They just grow and should not grow too much anyway. Like house plants.
Bonsai sit in very well draining substrate and are watered aggressively. The minerals are washed out quickly. Bonsai have to grow MORE than other plants during development phase. 99 % of bonsai are in development phase. They have to grow much to make it possible to style them quickly. They have to grow lots that can be cut off several times during a summer.
I definitely use three times the advised strength of fertilizer. I definitely use regular cheap fertilizer for normal plants. That is 10-10-10 or 20-10-10 or similar, anyway lots of nitrogen. And I feed every ten days to two weeks throughout the whole growing season. Compared to regular bonsai folks I feed about 20 to 60 (sixty) times more.
My trees look as happy as trees can look like. Yes, they grow much stronger than in other gardens and I have to cut off lots and lots. I think this is great because my trees can be developed much faster than others. My trees have no pests because they have very strong immune systems. So far I have not realized any damage from my super-feeding-program.
I feel that in America the following happened: During the past fifteen years the overwhelming majority of bonsai folks have changed from soil to modern substrate with their trees. But they are still applying the old wisdom concerning watering and feeding which was correct with soil. As a result many trees are suffering from drought and are starving. Nobody is telling people that with the new substrate they RADICALLY have to change watering and feeding schemes.
I hope this helps