Introduction
Hydroponics may be considered as the growing of plants in a soil-less medium with the roots in a water system containing an artificial nutrient supply. Many of us growing bonsai utilize an inorganic soil mix and simply water and fertilize trees with a solution of chemical fertilizer. Many bonsai grown in this "soil" thrive and develop as well as in soil mixes composed of significant amounts of organic materials and fertilized with organic and inorganic fertilizers. In a simple way these bonsai are really being grown hydroponically. My idea was to test whether plants grown in my normal bonsai mix and watered and fertilized "normally" would grow as well as in a hyrdoponic system.

An experiment
About two years ago, three identical Ficus microcarpa cuttings were potted into a soil of 100% small red lava. One was placed into a hydroponic bath system. A pump and timer automatically flushed water and hydroponic fertilizer through the pot three times daily for one half hour each time. The two other pots were placed nearby and watered with reverse osmosis water, as are all my other bonsai. Water was applied manually as needed, generally once each day. A chemical ferilizer such as Miracid or Miracle Grow was applied at half strength once a week, and a long-acting chemical fertilizer was also applied to the soil surface every two to three months.

No organic fertilizer was used on any of the trees.

When insects were detected, all the trees received appropriate insect sprays .

The plants were not trimmed or shaped in any way.

The experiment was terminated at 2 years and the photograph below shows the trees.

The results
The hydroponically grown tree is on the right and has a trunk of 3/4" while the two other trees have trunks of less than 1/2". In addition, the hydroponic tree has something like 5 times more foliage than the conventionally grown trees.

Conclusions
It is difficult to know why the hydroponically grown tree was more vigorous. Could it be that my normal watering is not as healthy? Perhaps, I am watering too much or too little? Perhaps my fertilizer regimen is not as good as it might be. Perhaps I need to be using fertilizer more often than weekly, or perhaps the fertilizer should be stronger than half strength. Or perhaps I need to add some inorganic material to my soil?

As is often the case, one experiment leads to more questions and to more experiments.

Responses
Dennis Howke of Spokane, Washington, concludes that my normal fertilization with half strength fertilizer should be modified to one quarter strength and used every day. Then the hydroponic and normally grown plants should grow at the same rate. Another way to do this is to use a fertilizer injector, a device that automatically adds fertililizer to the water, and to use this each day. Thus making the process of fertilizing less troublesome.

Over the last year I am currently using an automatic fertilizer injector and feeding my trees with each daily watering. So far results are very encouraging with excellent growth in all my bonsai and no apparent problems.