Timing, methods and principles for fertilizing bonsai

  Bonsai has less soil, so nutrients are limited and must be replenished constantly. Otherwise, branches become weak, leaves turn yellow, flowers are sparse and fruit is scant, which affects the ornamental effect. At the same time, bonsai plants need their growth suppressed, so generally they do not need too much fertilizer; too much makes branches and leaves grow too densely and affects the shaping. Therefore, fertilizing must be done reasonably and in the right amount. First, you must understand the fertilizer requirements of each tree species and the amount of fertilizer needed at different stages, so as to suit the tree and the time; second, you must understand the properties and composition of various fertilizers so as to achieve the expected results.

  As for the timing of fertilization, generally quick-acting fertilizers are applied during the period of vigorous plant growth, and slow-acting fertilizers are used during the dormant period. Fertilizing is not suitable during the plum rain period or the autumn rainy period. For topdressing during the growing season, it is best to do it on a sunny day when the potting soil is slightly dry, because at this time the potted tree is both hungry and thirsty, and the absorption effect is good. Fertilizing on rainy days or when the soil is wet makes nutrients easily lost and can also cause root rot.

  Bonsai fertilization, like that of potted flowers, even more needs to follow “light fertilizer applied frequently.” Especially when new roots are just emerging during the growing season, fertilizer that is too concentrated will dehydrate the plant roots and injure them, causing the plant cells to undergo “plasmolysis”; in mild cases some branches and leaves wither, and in severe cases the whole plant dies. Specifically: light means seven parts water and three parts fertilizer, and frequent means applying about once every week or so. When topdressing bonsai, first loosen the soil, using a trowel to break up the surface layer of the potting soil so as to help the fertilizer seep down and reduce loss; when fertilizing, make sure the fertilizer liquid does not touch the stems or leaves, and pour it along the edge of the pot. On the morning of the second day after fertilizing, “return water” should be given, which can avoid fertilizer damage.

  Bonsai fertilization mainly uses organic fertilizers. If a liquid fertilizer mainly based on nitrogen is needed, plant residues such as soybean cake can be placed in a vat or jar and fermented with water. If a liquid fertilizer mainly based on phosphorus and potassium is needed, animal-based impurities such as chicken manure, dead fish and plant ash are mostly put into a vat, water is added, and it is fermented. Fermentation time: in summer generally more than 15 days, and in autumn and winter more than one month.

  Bonsai fertilization needs to be determined according to the tree species, the height of the pot and the ornamental purpose. For example, for foliage-oriented bonsai such as five-needle pine, ivy, boxwood, elm and Japanese bush cherry, generally nitrogen fertilizer is the main one, with phosphorus and potassium fertilizers as supplements. But for foliage trees grown as bonsai, the leaves should not be too large or too thick, so fertilization must not be too frequent or too much. For flower-and-fruit bonsai such as wisteria, firethorn, crabapple, pomegranate, nandina and goji berry, which are mainly grown for flowers and fruit, in addition to nitrogen fertilizer, more phosphorus and potassium fertilizers should be applied, and fertilization should be frequent and plentiful.

  In order to promote strong branches and lush leaves in foliage-type bonsai, and bright flowers and large fruit in flower-and-fruit bonsai, foliar feeding can be carried out during the period of vigorous plant growth. For example, foliage-type bonsai can be sprayed outside the roots with 0.3% urea water; for flower-viewing and fruit-viewing bonsai, using 0.05% boric acid fertilizer as a base fertilizer during the bud stage and spraying the leaves with 0.5% superphosphate extract has a very good effect. In addition, when potting or repotting bonsai, some fully decomposed prepared organic compost can be added to the potting soil as a base fertilizer, generally applied once before spring sprouting to make the branches and leaves grow strong. For flower-and-fruit bonsai, fertilizer should be applied frequently during the flower bud differentiation stage and the fruit enlargement stage after flowering. At the same time, the following points should also be noted when fertilizing:

  1. Organic fertilizers must be fully decomposed before they can be used.

  2. Under no circumstances should concentrated fertilizer liquid be poured directly into the pot; it must be diluted to a certain degree before use.

  3. Newly potted bonsai that have not yet grown new roots must not be fertilized.

  4. Fertilize in the evening after the potting soil is slightly dry, and do not fertilize on rainy days.

  5. On the morning of the second day after fertilizing, “return water” must be poured.

  Fertilizer is closely related to plant growth and development. Especially for potted plants, because they grow in pots for a long time, root growth is limited by the potting soil, and the range for taking up nutrients is relatively small. A sufficient supply of fertilizer is necessary to ensure normal growth and development, so fertilization is even more important. Bonsai fertilization should grasp the following principles:

  1. Fertilization must be timely

  Timely fertilization means fertilizing when the flowers need fertilizer; when the plant's leaf color becomes pale and growth becomes thin and weak, fertilizing is most appropriate.

  2. Fertilization must be appropriate

  Fertilization must be applied differently according to the different growth stages of the flowers. For example, at the seedling stage, more nitrogen fertilizer is needed, the fertilizer water should be more dilute, and the frequency should be greater, so as to promote rapid and robust seedling growth; after the plant matures, more phosphorus and potassium fertilizers are needed. For foliage-viewing flowers, more nitrogen fertilizer should be applied to make the leaves tender green; for flower-and-fruit-viewing flowers, more phosphorus and potassium fertilizers should be applied to make the plants bloom early and bear fruit early, and also to make the flowers and fruit brightly colored.

  3. Fertilization must be accompanied by loosening the soil

  Before applying dilute liquid fertilizer to potted flowers, first rake the surface layer of the potting soil loose, and fertilize after the potting soil is slightly dry. After fertilizing, immediately spray the leaf surface with water to avoid residual fertilizer liquid polluting the leaf surface. On the second day after fertilizing, be sure to water once.

  4. Fertilization must follow the seasons

  In spring and summer, flowers grow rapidly and vigorously, so more fertilizer can be applied; after the beginning of autumn, flowers grow slowly, so less fertilizer should be applied; in winter, when they are dormant, fertilization should be stopped.

  5. Fertilization must follow the timing

  Fertilization of potted flowers should adopt the principle of “eat small meals more often” (that is, “apply light fertilizer frequently”). Generally, from early spring to the beginning of autumn, dilute fertilizer water can be applied once every 7-10 days, and after the beginning of autumn it can be applied once every 15-20 days.

  6. Fertilization must take temperature into account

  Fertilizing should be done on sunny days. Potted flowers should not be fertilized around noon during high summer temperatures, because the potting soil temperature is relatively high and applying topdressing easily injures the roots; application in the evening has the best effect.