Bonsai Confusion for Beginners:Fertilizer
By Wayne Greenleaf
This article is a break from my usual format. I don’t have confusing advice from various authors to juxtapose for this article. Nor are any needed. The subject is confusing enough on its own, if, like me, you don’t start with much knowledge of chemistry and plant physiology.
"Major Nutrients", "Secondary Nutrients", "Minor Nutrients", "Macro-Nutrients", Micro-Nutrients", N, P, K, Ca, Mg, S, Zn, Fe, Mn, Cu, B, Mo, Cl, and on, and on. There is just a lot to learn about the elements necessary for our trees to live, grow and remain healthy. All authors point out the importance of fertilizing bonsai. For example, in one of the earlier English language books, Murata says, "Without proper fertilizer application, proper plant growth can not be expected."1
While most bonsai authors talk about watering and placing bonsai for the health of our trees, most do not emphasize that water and light are the most important elements for plant growth. The first is water. "Water is the most important plant food element by far. It makes up approximately 90 percent of the weight of plants and is the one most limiting factor in plant growth. All plant food elements are dissolved in water and move into and throughout the plant in a water solution. ... Only about 1 percent of the water adsorbed is actually used by the plant. The other 99 percent is lost through the leaves and stems as water vapor in a process called transpiration."2 "....Photosynthesis uses water in the manufacture of food and could not occur without it."3
The second most important element is not usually mentioned at all by our books; it is carbon dioxide from which the trees extract carbon. It is present around our trees all of the time and we all take it for granted. However, in horticulture, nursery producers recognizing the importance of carbon, are enriching the CO2 in greenhouses to increase the growth rate of some plants. Carbon dioxide and water exposed to light in the presence of chlorophyll produces the real food for plants which is sugar and is used or stored in the trunks and roots as carbohydrates.. Excess oxygen is released as a by-product. (Some oxygen is used by the plant for respiration.)
So the most important elements for a plant to produce food are water, carbon dioxide and light. The remainder of the elements are really building blocks for the plant structure, leaves, flowers, fruit or for chlorophyll itself. That does not diminish their importance, and since everyone else calls them "food" for our trees, I probably will too.
The Major Elements are variously grouped by authors. Deborah Koresoff, in addition to Carbon (C), Oxygen (O) and Hydrogen (H), lists Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Sulphur (S) and Magnesium (Mg) as the major elements.4 The Sunset book on diseases lists the same elements as Major and Secondary Nutrients.5 However they are grouped, they are listed in the order of the quantity used by plants and trees.
N-P-K are the familiar elements listed on commercial fertilizer bags as a percentage or pounds per hundred weight. Nitrogen (N) encourages above ground vegetative growth, gives the leaves a dark green color and also seems to regulate the use of other elements. Phosphorus (P) encourages plant cell division, flowers and seeds do not form without it, hastens maturity, encourages root growth, and increases resistance to disease.6 Potassium (K) acts as a catalyst for other elements, modifies the effects of nitrogen, encourages a healthy root system, is essential for starch formation, is necessary for development of chlorophyll and improves the quality of roots and fruits.
Some of our bonsai books recommend fall feeding with fertilizers heavy in phosphorus and potassium, especially for flowering and fruiting trees.7 Having read this recommendation, I started paying more attention to the relative values of the fertilizer. I was looking for higher P and K for my flowering bonsai. What happened is an experience that I wish to share. First I noticed that "Tomato Food" had higher values of these two elements. Then "Super Bloom" could be found on the market with a very high relative value of Phosphorous.
I eventually noticed that Wal-Mart had Muriate of Potash (0-0-60) in a 5 pound bag and Triple Super phosphate (0-46-0), also in a 5 pound bag. The Potash only indicated an application rate of ½ pound per 100 square feet. How big is a bonsai pot? What fraction of 100 sq. ft. is a bonsai pot? The Super phosphate suggested 1 - 2 ½ pounds per 100 square feet, and also said 1 - 2 Tablespoons per gallon of soil for potted plants. It was easier to visualize (guess) the gallons in my bonsai pots. I mixed two bags of the Potash with one bag of the Super phosphate, stored them in another container, and was ready last fall.
Last September and November, I think, (I don’t keep very good records) I applied the mixture at the rate of 1 Tablespoon per gallon of soil. If I wasn’t sure, which was most of the time, I went light. While neither of these elements are supposed to burn roots, these are pretty high concentrations and I didn’t want to overload the soil with salts.
This spring and summer I have had trees bloom that have never before bloomed for me. It could just be coincidence and they are now mature enough to bloom. Other trees seem to be blooming heavier, and one tree produced fruit for the first time. Coincidence? Well, I could cut out the fertilizer routine this fall and watch what happens next spring. B..U..T, I don’t think that I will. In fact, Koreshoff recommends "late summer" through fall for heavy phosphorous and potassium, so I’m adding an August feeding with the mixture. It’s not scientific, but then neither is most of what we do with our trees, as enthusiasts.
If you decide to give the idea a try, let me know the results. We are all impressed more by trees in bloom than by words on a page.
REFERENCES:
1. Murata, Kyuzo. Bonsai: Miniature Potted Trees, Shufunotomo Co., LTD., 1964.
2. Reiley, H.E. and Shry, C.L., Jr., Introductory Horticulture, Fourth Edition, Delmar Publishers Inc., 1991.
3. Reiley, H.E. and Shry, C.L., Jr., Introductory Horticulture, Fourth Edition, Delmar Publishers Inc., 1991.
4. Koreshoff, D., Bonsai: Its Art, Science, History and Philosophy. Timber Press, 1990.
5. Gilberg, L. (Ed.), Garden Pests & Diseases, Sunset Publishing Corporation, 1993.
6. Reiley, H.E. and Shry, C.L., Jr., Introductory Horticulture, Fourth Edition, Delmar Publishers Inc., 1991.
7. Koreshoff, D., Bonsai: Its Art, Science, History and Philosophy. Timber Press, 1990.