We all know that we must fertilize our bonsai and that nitrogen, potassium and phosphorous are essential ingredients in any fertilizer package we offer our plants. It is less obvious that the plants also require tiny amounts of several other elements for optimum growth. Examination of a package of Miracle Grow fertilizer reveals that it is fortified by a cocktail of these elements, some of which are familiar such as copper and iron and some that are not such as manganese and molybdenum.

Suppose that you are a scientist and have been asked whether a trace amount of the element vanadium is essential for growing corn. Your first thought is that it is not because vanadium is rarely found in soil and corn grows great just about everywhere. As a scientist you know that you must back up your opinion with experimental data. How would you do this? You would prepare three soils, one with no vanadium a second with a little vanadium added and a third with a little more vanadium added. You would plant corn seeds in each of the soils and compare how well the corn plans grew. If they all look about the same you conclude that vanadium is not essential for growing corn. If, on the other hand the group with a little vanadium is growing better and if the third group with even a little more vanadium is growing the best then the conclusion is that vanadium is essential for growing corn.

Two things stand out in this hypothetical experiment. First is that opinion is not enough to make a convincing case, no matter how reasonable it might sound. Second is the inclusion of a group of seeds planted in soil with no vanadium which served as a standard against the vanadium enriched soils can be measured. Many things can influence how plants grow such as the amount of light, fertilizer and water. The control group showed that the improved growth of the soils with vanadium, if any, was only due to the presence of the vanadium and not one of these other factors.

You might ask, what in the world has all this to do with bonsai? Most of the people in bonsai are not scientists so there is little convincing data to be found on many of the opinions that we hold dear. Instead we find a lot of strongly held opinions just aren’t true. You will not get far on your bonsai journey until you hear comments like ”I changed from fertilizer A to fertilizer B and my trees are growing much better” With no direct comparison of some trees fed with the old fertilizer and some fed with the new fertilizer it is not possible to tell whether the improved growth that really happened was due to the new fertilizer or to more favorable weather, the amount of water or more sunshine. This makes for a lot of

confusion on the part of folks new to bonsai and adds a layer of unnecessary mystique to what should be straight forward management of your plants.

The area of soils composition is deluged with opinions. Soil mixtures can include organic components (meaning once alive, such as fir bark or compost) and inorganic components (meaning never lived such as lava or pumice) Current opinion says that you should never include organic components because they can decay over time and this process robs fertilizer that your tree needs. Sounds good, but where is the data? Decayed organic material can affect water drainage which is not good and can influence your watering schedule but that does not affect how well fertilizer is retained by the soil. Another related opinion is that organic material is needed in the soil mix to “retain” the fertilizer. An opinion occasionally heard is that you should include inorganic material which has sharp edges because growing roots will be split by the sharp edges and this leads to denser root balls. Sounds good, but has anyone looked at roots and compared the roots of trees grown in sharp soils with roots grown in media with no sharp edges to see whether this hypothesis it true? Where is the controlled experiment where direct comparison can be made between the two types of soil?

So frequently we pot all our trees into a new soil mix and discover that they are growing better. With no control of plants left in the old mix we cannot tell whether the improved growth of the trees in the new mix due solely to the new mix or are they due to the fact that the weather is warmer, you have increased the amount of fertilizer used, you water more frequently or many other things that have nothing to do with the new mix.

Everyone agrees that you should never use garden soil as a component in your soil mix Thirty years ago a popular mix was one third each of garden soil, sand and leaf mold. The mix requires careful management of water since it may not drain well. Here there is a sort of a control available. Pictures of trees from this era show that magnificent trees can be very successfully grown in this mix.

Fertilizer is another subject of great debate There are adherents who claim that the use of only organic fertilizers such as cotton seed meal or fish emulsion are worth considering and others who claim that inorganic fertilizers are necessary for best results. Again, sadly, there are few if any controlled experiments. All trees require nitrogen and it is likely that they are not too fussy about where they get it. The difference between the two classes of fertilizers is probably small or nonexistent because splendid bonsai trees can be grown using both types of fertilizers, but this an area crying for data.

Where does the newcomer to bonsai turn for help in growing bonsai? The newcomer is best served by knowing that your bonsai tree really wants to grow for you and become the splendid bonsai that you want. It does this by having its basic needs met. These are a soil that drains well, enough water to keep the soil moist, sunlight and fertilizer. A valuable resource to the newcomer is the techniques which local growers use to meet these needs. They should beware of advice that starts with “the only way to…” or “I do this because….” because good data to support the comment may be lacking.