Bonsai care (fertilizer)

For normal growth and development, besides carbon (C), hydrogen (H) and oxygen (O), which a plant takes from the air and water, a plant must get nutrients, macro- and microelements, from the soil. The macroelements are nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca); various microelements are also needed in very small doses: magnesium (Mg), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), boron (B), manganese (Mn), sodium (Na) and other elements. All of these elements are vital to the plant’s existence, especially the macroelements. An excess or a shortage of any one of them has a marked effect on the plant’s development. For example:

Nitrogen is needed to regulate growth, for the leaves and for fruiting. A nitrogen deficiency soon shows up as slower growth. An excess prolongs the growth of new shoots, which weakens winter hardiness. Nitrogen-rich fertilizer is not applied in the second half of the growing season.

Phosphorus promotes the plant’s development and root growth, and strengthens its tolerance of drought and frost.

Potassium gives the plant tolerance of stress (very high or low temperatures, too much or too little moisture). The right amount of potassium improves the buds’ ability to overwinter, as well as the plant’s resistance to fungal and bacterial diseases.

Calcium is essential for normal metabolism in the plant.

With bonsai, because there is so little soil in the pot, the nutrients are soon used up. So regularly applying a fertilizer that contains all of these elements is as essential as watering. Without supplementary feeding a plant develops poorly, its leaves and needles lose their color, and it falls prey to disease more easily.

You can use either organic or mineral fertilizer on bonsai, but you must not mix the two together and apply them that way. There are fertilizers made especially for bonsai that contain all the necessary elements. Such fertilizer can be either liquid or solid, in granules. Liquid fertilizer is dissolved in water at a set dose and the plant is watered with the solution as usual. Plants absorb liquid fertilizer quite quickly, so on deciduous and fruiting trees it is applied once every 2 weeks, and on conifers once every 3 weeks. Granular fertilizer acts over a longer period. It is either mixed into the soil or put into special small baskets placed on top of the soil. With each watering some of it dissolves and gradually feeds the bonsai.

If you can’t find such fertilizer, you can use a balanced compound fertilizer sold at garden centers or flower shops. As a rule, such fertilizers contain all the elements plants need. For bonsai it is best to use one that dissolves easily in water, as it is more convenient to use. The packets always state the composition in percentages and how much water to dissolve it in. When applying a fertilizer that does not dissolve in water, take great care and work out the right dose, because too much can kill the plant. Feeding normally begins in early spring and ends in autumn. Never fertilize a freshly repotted plant. Fertilizer may be applied only 4–5 weeks after growth starts, once the bonsai has rooted well.