Fertilizing Your Bonsai

When should I fertilize my bonsai? With what should I fertilize my bonsai? At what dilution should I fertilize my bonsai? How often should I fertilize my bonsai? Should I fertilize my bonsai? These questions and more crop up countless times as bonsai enthusiasts look ahead to long-term care for their trees. Here is a general outline you can use to help you make these important decisions.

First, it may be helpful to give a little background on fertilizers and how they benefit your plants. All commercial fertilizers can be described as a ratio of three elements: Nitrogen (N), Phosphorus (P), and Potassium (K), along with various Trace Elements such as ferrum, manganese, zinc, etc. These three elements (known colloquially as N-P-K) are assembled in various ratios expressed as three corresponding numbers. Thus, Peter’s Brand 20-20-20 is 20% Nitrogen, 20% Phosphorus, and 20% Potassium. These three key substances are part of six total elements* knows as macronutrients.

Fertilizers may be further classified as organic or inorganic.

Deciding when to fertilize and with what to fertilize depends upon many factors, not the least of which is your tree’s age and where it is with regard to refinement and your ultimate design goals. Look at your bonsai, and decide where it is among these categories:

Raw material, or ‘Pre-bonsai’: Normally this stage receives the most fertilizer of all. Trunks need thickening, so one is aiming for maximum foliar and root growth in order to bulk up all the design elements. Trees in this stage might still be in the field or in large training pots or grow boxes.

Somewhat refined: Probably this tree has its basic trunk and primary branch placement completed. It may or may not be in its final bonsai pot. At this point ramification is the major design goal, along with careful development of foliage masses that are ‘cloud like’ and evoke the image of a mature tree.

Highly refined: At this point the tree is very close to its maximum potential for beauty. From this point on one is trying to maintain gentle, even growth.

Here is a list of some common fertilizers used in bonsai, along with their benefits and uses:

Peter’s 20-20-20: A good all-around fertilizer, used by many as their sole fertilizing source. As you can see by the N-P-K, very high in Nitrogen, so this is excellent for raw material and semi or somewhat refined bonsai. Tends to reduce acidity, so beware for acid loving plants such as azalea.

Osmocote: A pellitized fertilizer, usually small golden balls. A slow release feed, this is excellent stuff for all manner of bonsai. It contains trace elements such as

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