Part 4 of a series by Eugene Howell
Of the four basic requirements for a bonsai tree to survive and be healthy, we’ve already discussed three of them in previous posts that are linked to at the bottom of this page. To have a better understanding of how to bonsai, let’s now turn our attention to soil.
Bonsai soil must satisfy three essential requirements for the tree: good drainage, proper pH and good nutrients. The soil needs to be able to drain off excess water, as discussed in my previous article. It also needs to have a pH level that is acceptable to the plant, and the soil must provide nutrients that the plant can absorb and eventually convert to food (complex sugars).
The pH scale measures alkalinity and acidity. The scale runs from 0 to 14, with the lower end of the scale indicating acidic conditions and the higher end indicating alkaline conditions. A measurement of 7.0 is considered neutral; neither acid nor alkaline. 5.5 to 6.5 is good for bonsai trees and anything above 7.0 or below 5.5 is not.
Most plants will do very well in this slightly acidic soil with pH levels of 5.5 to 6.5. While it may seem that a neutral soil (ph 7.0) would be desirable, it’s actually nearly impossible to put such a soil mix together. Most plants have an ability to easily adapt to a slightly acidic soil, however, the opposite is not true. Few plants can adapt to an alkaline environment. One of the excellent aspects of bonsai soil is that, when properly mixed, it ends up with a good, quality pH without additional effort. Both sand and Turface are neutral and ground pine bark is slightly acidic. Thus the resulting mixture yields a quality pH soil, right where you want it.
Every plant needs several major elements and a whole bunch of minor ones in order to thrive. Bonsai soil, however, has very few of these, so your trees will be greatly dependent on you for these essential elements. So the question at hand is “What are they and where do we get them?”
The three major elements needed by all plant life are nitrogen (N), phosphorus (P), and Potassium (K). These are the elements that fertilizer manufacturers refer to when they print 3 number sequences like “6–10–5” or “10-5-8”on their product packaging. The first number is the percentage of nitrogen. The second number is the percentage of phosphorus, and the third number is the percentage of potassium. If you look on the side or back of a fertilizer package you’ll find a table that contains a complete listing of all the elements in that particular mix. It’s helpful if the fertilizer contains such things as iron (Fe), magnesium (Mg), manganese (Mn), copper (Cu), zink (Zn), boron (B), calcium (Ca), molybdenum (Mb), and chlorine (Cl). The more of these that are in the fertilizer, generally the more it will cost, but your plant will be healthier.
Lacking even just a couple of these minor elements can cause many plants to exhibit symptoms of ill health. For example, if either magnesium or manganese are deficient, a plant may show a yellowing of the leaves. So it’s best to always use a fertilizer containing all these minor elements.
Two final points on the subject of fertilizing; first, some fertilizers (most of them) are fast release and some are slow release. One that is fast release will release all of its elements over a period of two or three weeks. During the summer, when you water every day, this means that all the fertilizer has been washed from the soil in a relatively short period. A slow release fertilizer releases the nutrients over a period of months. Even though you water daily, the encapsulated grains remain in (or on) the soil for many weeks and continue to release nutrients to the tree. This gives your plant the ability to achieve its maximum growth rate over the entire growing season.
On the other hand, you can use water soluble fertilizers to maximum benefit only if you know the best way to do so. When you use these (and water daily) the fertilizer will completely wash out of the soil within 2 to 4 days. If you use water soluble fertilizer only once per month as is recommended on the container, your bonsai will grow in spurts and will not achieve its maximum growth rate. The best strategy for the use of this type of fertilizer is to mix it at ¼ the concentration shown on the package, and use it once per week rather than once per month. Your bonsai trees will then receive a constant supply of nutrients.
Don’t fall into the trap of thinking that “if a little fertilizer is good, then more is better”. That’s a good way to kill your bonsai. Too much fertilizer will “burn” the roots.
By having a good draining soil with proper pH and a regular fertilizing schedule, your bonsai trees will be healthy and will grow well.
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