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Proper Fertilization Techniques For Bonsai

By Randy Clark, Charlotte, NC, USA
The Bonsai Learning Center
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A proper program of fertilization is important for the cultivation of all types of plants, but is of particular importance when growing bonsai. There are two reasons for this. First, bonsai are grown in containers. This means there is very little space available from which the roots can obtain nutrients. Secondly, the soil mixtures traditionally used for proper bonsai cultivation are made up primarily of drainage materials (sand, rock, hadite, turface, etc.) and do not contain large amounts of organic materials that would hold onto nutrients or decompose and release nutrients into the soil.

It is therefore important to place your bonsai on a regular feeding schedule during the growing season. The plants require nutrients when they begin to grow and push buds in the early spring, and will continue to require feeding throughout the summer and into the fall (although in the fall the type of nutrients you provide will change (see below). Feeding may be discontinued during the winter months for all temperate plants and greatly reduced for indoor/tropical varieties. A temperate plant which has gone dormant for the winter, (dropped its leaves), is "sleeping" and like a hibernating bear, does not require food. Pay attention however,... when the bear and the bonsai wake up in the springtime, they will both be hungry.

Nutrient Forms

Generally speaking nutrients for your bonsai are available commercially in two forms, organic and inorganic. Which type you use is largely a matter of personal choice. We will discuss the pros and cons of each below. Regardless of which form you choose, they should all include both macro and micro nutrients.

Macronutrients - Nitrogen, Phosphorus & Potassium

All fertilizers, whether the are organic or inorganic in nature must contain three primary elements which are vital to the trees health. These are Nitrogen, Phosphorus and Potassium. The amount of these ingredients which any given fertilizer contains is reflected in a series of three numbers, usually printed on the package. For example: 15-10-6 indicates that the fertilizer contains 15 parts Nitrogen, 10 parts phosphorus and 6 parts Potassium. The numbers may vary depending upon what you buy, but the order will always remain the same... Nitrogen first, Phosphorus second and Potassium third.


Plants usually absorb more nitrogen from the soil than they do other elements. It is nitrogen that produces rapid growth and gives the leaves and stems a healthy, deep green color. If a plant has insufficient nitrogen, the newer shoots will use up whatever nitrogen there is, causing the older leaves to turn yellow. Young plants which need to develop are usually fed a high nitrogen fertilizer to promote abundant green growth. More mature bonsai are fed with a mixture which contains reduced amounts of nitrogen.


Plants need phosphorus during all phases of their growth. However, this element is particularly needed for the formation of seeds, flowers and fruit. It helps the plants to store energy for the coming winter and to harden off roots and buds. It is therefore a good idea to feed your bonsai with a fertilizer high in Phosphorus (superphosphate) in the latter part of the growing season (late summer to fall). High nitrogen fertilizers used in the fall would only produce soft green growth which would freeze off during the first frost.


Potassium or potash, is essential for plants because it helps them to increase disease resistance. It improves stem and trunk rigidity and it helps plants to overcome poor weather or soil conditions. It generally makes plants more vigorous.


No matter what their form, all fertilizers contain some or all of the nutrients elements that bonsai need in order to grow. There are 16 beginning with carbon, hydrogen and oxygen which are generally provided by the atmosphere. The macronutrients of Nitrogen, Phosphorus and Potassium and micronutrients which include: calcium, copper, iron, manganese, molybdenum and zinc. These micronutrients are essential to the plants health, but are only needed in small amounts. Many commercial fertilizers come with micronutrients added or micronutrients can be purchased separately and added to the soil in bonsai containers on a yearly basis.

Organic Fertilizers

Organic fertilizers improve soil structure and release plant nutrients slowly, which reduces the possibility of over fertilizing (a definite advantage for new, overzealous bonsaists). The normal procedure is to make small balls or cakes of the desired organic substance and place these cakes on the tree. However, since they are organic in nature they can grow unwanted fungus or mold and serve as a home for insect larvae. Sprinkling a little powdered insecticide helps keep this under control. How well they work depends upon how warm the soil gets and the level of microbe activity in the soil. Those most commonly used for bonsai are:

Bone meal: This decomposes slowly and releases phosphorus. Its natural alkalinity helps to neutralize the acidity of peat-based or acidic soil mixtures.

Cottonseed meal: This is a slightly acidic by-product of cotton manufacturing. It is good for use on acid loving plants such as azalea, camellia and rhododendron.

Blood meal: This is dried, powdered blood from cattle slaughterhouses and is a very, very rich source of nitrogen. It also contains several trace elements. You should be careful to not overuse this product.

Fish Emulsion: This blend of partially decomposed, finely pulverized fish is high in nitrogen and also contains several trace elements. You can boost plant growth by applying it in late spring, but like the blood meal, it is easy to burn your plants with this product... be careful. A special caution should be observed if you have raccoons living in your neighborhood. We can personally relate the tale of a raccoon in our back yard who unpotted about 6 of our bonsai that had been freshly fertilized with fish emulsion because he was certain that we had hidden a fish in the pots.

Inorganic Fertilizers

Inorganic fertilizers (chemicals) come in different forms: dry, liquid, slow-release, pelletized, plant stakes and soluble solutions, among others. Both the forms and formulations available in the marketplace are extensive and permit you to choose according to your own preferences. You may like a dry fertilizer to incorporate with a potting soil mix or a liquid fertilizer to apply from a hose. Still others may opt for a slow-release fertilizer that needs to be applied less frequently. The actual fact is that most bonsaists choose to vary their feedings with both organic and inorganic fertilizers.

Fertilization Frequency

Here at the Bonsai Learning Center we fertilize our trees on a bi-weekly basis. Because of the large number of plants we must fertilize, we have chosen to use a chemical fertilizer which can be applied through a hose siphon system. We don't believe its better... or worse,.... just more efficient for our purposes. Because we are not always as dutiful about applying fertilizers as we should be, we also supplement these feedings with time release fertilizer tablets (Sierra tablets) which are similar to osmocote pellets, but can be placed below the soil level. On some of our more mature bonsai we also use an organic fertilizer (Bio-Gold) which is manufactured in Japan specifically for use with bonsai and contains less nitrogen than others.

The debate between bonsai people over what type of fertilizer works best has always been a hot one. In the final analysis, you will have to make your own choice. What you use is immaterial to the plant so long as you provide the required micro and macro nutrients described above, in a form you bonsai can absorb. Whatever you decide, make sure you are doing it on a regular basis.

Randy Clark, 60, has been learning the art bonsai for more than a quarter century and for the past decade, has traveled throughout the United States and Europe teaching the subject. He strongly encourages his students to develop an individual approach to the art .

"One must have more than a simple classical understanding of the principals of bonsai design if one wishes to grow and develop in the art. It is certainly important to honor our Japanese teachers by understanding the time tested principals upon which classical bonsai design is based,... but it is even more important that each student strives to bring new insights into what they do," he said. "One must learn and understand when to apply the rules as well as when to bend them. Bonsai is an art... and all art forms, by definition, are interpretive."

During his thirty plus years of involvement with bonsai, Mr. Clark has spent seven of them serving as a vice president of the National Bonsai Foundation in Washington D.C. as well as two terms as president of the Minnesota Bonsai Society and as Chairman of the 1987 International Bonsai Conference which was held in Minnesota. He also served two years as the managing editor of Bonsai Magazine, the official publication of Bonsai Clubs International and is the author of Outstanding American Bonsai, a book, published by Timber Press in Portland, Oregon. His bonsai have won numerous first place and best in show awards at both the local and regional level.

For nine years he operated White Dragon Bonsai Studio out of his former home in Minnesota. In 1995 he relocated to North Carolina and now operates The Bonsai Learning Center in Charlotte. He has studied with such well know national and international bonsai authorities as: John Naka, Toshio Saburomaru, Chase Rosade, Keith B. Scott, Susumu Nakamura, Horst Krekeler, Mas Imazumi, Hu Yun Hua, Qing Quan Zhao, Marion Gyllenswan, Vaughn Banting, and many others.

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