How to Fertilize Small Bonsai: Methods and Precautions Explained

  Because bonsai have limited soil, fertilization must be timely, otherwise it easily causes leaves to turn yellow, decline, and branches to wither. The amount of fertilizer varies with the type of plant. For small bonsai grown mainly for their flowers, a lighter fertilizer should continue to be applied after flowering to encourage more blooms the following year. For small fruit-bearing bonsai, a slightly stronger fertilizer can be applied, and 1—2 applications of light fertilizer should be given before flowering to ensure an adequate nutrient supply. For deciduous bonsai, generally do not apply much fertilizer, otherwise it will cause excessive growth and affect the tree's shape.

  Bonsai are generally fertilized around Qingming (early April) using the immersion method with some thin liquid fertilizer, such as green manure and cake fertilizer. For foliage types, nitrogen fertilizer is primary with phosphorus and potassium secondary, while flowering and fruiting types should be given more phosphorus and potassium fertilizer. Fertilization should be done on sunny days when the potting soil is dry. During the plum rain season, because temperature and humidity are suitable, branches and buds grow quickly, so nutrients should be replenished in time.

  Small bonsai plants are cultivated in pots, so their space and soil are limited, and natural nutrients are also limited. For the normal growth of potted plants, replenishing nutrients is absolutely necessary, so fertilization is also a very important part of the daily management of small bonsai.

  The three elements of fertilizer commonly referred to are: nitrogen, phosphorus, and potassium. Nitrogen can promote the growth of branches, leaves, and roots. Phosphorus not only helps the growth of roots, branches, and leaves, but is even more important for promoting flowering and fruiting in flowering and fruiting bonsai. In addition, potassium is important for the trunk, roots, flowers, fruit, and the overall growth of the plant.

  Besides the three main elements of nitrogen, phosphorus, and potassium in fertilizer, plants actually also need thirteen other important elements to grow smoothly, namely carbon, oxygen, hydrogen, calcium, iron, magnesium, calcium, manganese, boron, zinc, sulfur, copper, and chlorine. Among these sixteen elements, carbon is absorbed through photosynthesis in the leaves, from the leaf stomata in the form of carbon dioxide CO2. Oxygen is absorbed through respiration from the leaf stomata or roots in the form of O2. The other fourteen elements are generally absorbed by the roots in a form dissolved in water. Apart from nitrogen, phosphorus, potassium, carbon, and oxygen, the other elements hydrogen, calcium, iron, magnesium, calcium, manganese, boron, zinc, sulfur, copper, and chlorine are needed in smaller amounts, and plants can absorb these elements from water and soil, so except under special circumstances they are rarely supplemented separately. The regular "repotting" work for bonsai also replenishes these elements.

  Commercial fertilizers generally use numbers to indicate the content of nitrogen, phosphorus, and potassium, for example:

  20–5–5 means nitrogen 20% - phosphorus 5% - potassium 5% (high nitrogen content, suitable for foliage types and pine and cypress types, can make leaf color green and glossy)

  5–20–20 means nitrogen 5% - phosphorus 20% - potassium 20% (high phosphorus and potassium, suitable for flowering and fruiting types, can promote flower bud differentiation, flowering, and fruiting)

  20–20–20 means nitrogen 20% - phosphorus 20% - potassium 20% (balanced nitrogen, phosphorus, and potassium content, suitable for all plants)

  So when purchasing, choose the appropriate fertilizer according to the tree species and needs.

  Fertilizers are roughly divided into organic fertilizers and chemical fertilizers. For general bonsai, using organic fertilizers is safer, less likely to cause fertilizer burn, but prone to odors and flies. Chemical fertilizers, because their fertilizing effect is too strong and improper application easily causes fertilizer burn to potted plants, are used less. There are now some synthetic fertilizers on the market with good effects; as long as they are used according to the instructions on the packaging, the effect is good, they are not prone to fertilizer burn, and they do not produce odors or flies.

  Production and use of organic liquid fertilizer: Use commonly sold organic granular fertilizer at a 1:10 ratio with water (volume ratio), soak it in a sealable plastic bucket, place it in a cool place to ferment for 30 days, then it is ready to use. When using, measure the liquid fertilizer with a measuring cup and dilute it with clean water at 1:10. Use a commercially sold fertilizing watering can (shaped like a watering can but with a very small spout) to pour the diluted organic liquid fertilizer onto the potting soil. The best method for using liquid fertilizer is after watering the bonsai once in the morning, wait until the bonsai has been in sunlight and by the afternoon the potting soil has reached a half-dry state, then use it, because the bonsai is already in a state of greatest water demand. At this time, the liquid fertilizer poured into the potting soil will be immediately absorbed and used by the roots. The effect of using liquid fertilizer is remarkable; within 3~7 days the fertilizing effect can be immediately reflected. As long as the dilution ratio is correct, it is not prone to fertilizer burn. Use it once every 7~14 days.

  When should fertilizer be applied? Generally, plants produce an annual "growth cycle" with the changes in climate through the four seasons of the year, so the timing and amount of fertilization must also match the plant's "growth cycle" in order to be effectively used by the plant. The timing and fertilization amounts of the plant growth cycle are roughly explained as follows:

  1. Vegetative growth period: (April to June) This is from new buds swelling and sprouting to new buds stopping and elongating, until branch and leaf growth is complete. During this period, watering and fertilizing are key points in bonsai management. However, fertilizing in early spring is unrelated to the growth of spring buds, because spring fertilizer can only be used by the plant after the new leaves have fully expanded. The energy needed when spring buds sprout relies on nutrients stored from the previous year's autumn fertilization, and the nutrients stored from autumn fertilization must be drawn out and used with the help of water, so watering management during this period is very important. Once the new leaves have fully expanded and the leaf area has increased, fertilizer demand rises sharply and attention must be paid to fertilizer supplementation. Replace the surface fertilizer at least once a month. The application amount is the general amount from April to mid-May; from mid-May to the end of June, in addition to the basic surface fertilizer, weekly liquid fertilizer supplementation can be added.

  2. Reproductive growth period (July to August) Trees of a certain age, after passing the vegetative growth period, will begin flower bud differentiation in order to reproduce, so this period is called the reproductive growth period. When the new shoots of the plant stop elongating, leaf buds differentiate again in the leaf axils and at the branch tips, and when these leaf buds transform into flower buds, it is called flower bud differentiation. Flower bud differentiation varies in timing depending on tree species and local climate (not elaborated here), but most tree species concentrate flower bud differentiation between July and August. During this period, flowering and fruiting bonsai should be given a flowering and fruiting fertilizer low in nitrogen and high in phosphorus and potassium, to make the plant's flower bud differentiation more complete, so that more beautiful flowers can bloom and more and larger fruit can be produced the following spring. For other bonsai tree species during this period, apply a small amount of surface fertilizer and replace it once a month.

  3. Nutrient storage period (September to mid-November) After entering September, daytime temperatures are still high, but after nightfall the temperature drops rapidly, forming a large and obvious day-night temperature difference. This is the period most suitable for plants to synthesize and store the carbohydrates produced by photosynthesis. The plant root system also develops most actively, and this is also the most important period for bonsai fertilization management. If the carbohydrates stored by the plant during this period are insufficient, it will clearly be reflected in weak and uneven sprouting of next year's spring buds, and miscellaneous trees and deciduous trees are prone to losing small branches and other phenomena. Therefore, during this period, plants must be given sufficient fertilizer, sufficient sunlight, and maintain a healthy leaf area for photosynthesis, so that sufficient carbohydrates can be stored to overwinter. So from September to the end of October, in addition to a larger amount of surface fertilizer, weekly liquid fertilizer supplementation can be added. From early November to mid-November, begin reducing surface fertilizer and stop liquid fertilizer.

  4. Dormant period (mid-November to March) After entering the dormant period, some evergreen pine and cypress tree species do not have a very obvious dormant period, and a small amount of fertilizer is still harmless, but deciduous miscellaneous trees need to stop fertilization, and management should focus on water management. Deciduous trees often die or lose branches in winter from water loss or excessive waterlogging…

  Precautions for fertilization:

  1. Use according to the instructions on the fertilizer packaging, and adjust the amount and frequency according to pot size, tree species, and fertilizer demand.

  2. A plant will not necessarily die without fertilizer; at most it will develop poorly, but excessive fertilization… will cause it to wither and die.

  3. Bonsai that have just been repotted must not be fertilized within one month; wait until their roots and leaves can metabolize normally before fertilizing.

  4. For miscellaneous tree bonsai, fertilize two weeks before defoliation to promote enough energy for growing new buds, but after defoliation and before new buds open their leaves, do not fertilize.

  5. Do not fertilize when the plant is diseased or weakened.