Like every living being, bonsai people also need nourishment. The little soil in small pots can be quickly depleted of the nutrients that the tree would need, so we must use fertilizer in the cultivation of our bonsai, in order to maintain the right balance.
We can divide the nutrients into two groups: macroelements and microelements.
The macro-elements are marked with the abbreviation NPK which corresponds to nitrogen (N), phosphorus (P) and potassium (K).
Nitrogen (N): it is very mobile and quickly reaches all the leaves, promotes the growth of the stem. Symptoms of deficiency is the pale green colour of the leaves, especially in the lower branches.
Phosphorus (P): Symptoms of deficiency may be the purple-red color on the leaves and an insufficiently developed root system.
Potassium (K): appropriate doses make the bonsai resistant to high summer temperatures. Symptoms of deficiency are: yellow spots on the leaves, especially on the edge, poor development during growth and irregular ripening of the fruits.
Calcium (Ca): is the substance that strengthens the plants. We can divide the plants into two groups: calcium plants (which actually need calcium) such as legumes and calcifuges which need less calcium, such as acid plants (azaleas, rhododendrons, camellias, gardenias, heather, etc.). The lack of calcium causes yellowing, curvature and foliar withering; in acidophilic plants, an excess of calcium causes yellowing of the leaves.
iron (Fe): together with magnesium it represents an essential element of the chlorophyll molecule, it also regulates various vital processes for the plant. Its deficiency (chlorosis) can manifest itself with the yellowing of the leaves starting from the youngest ones.
magnesium (Mg): together with iron it represents an essential element of the chlorophyll molecule. Deficiency can occur on older leaves by presenting areas bleached in white or yellow or leading to premature defoliation.
Sulphur (S): it participates very actively in the respiration of the plant and is present in rainwater. In poorly drained soil, sulphur is transformed into sulphite, which becomes very toxic to the plant. The lack of this element can manifest itself with the uniform yellowing of the leaves and with a stunted growth of the plant.
Boron (B): participates in the formation of roots, flowers and fruits. Its ease of absorption means that the deficiency in the soil is difficult to detect. Its lack can lead to death of twigs and new shoots.
manganese (Mn): participates in the formation of the molecule of chlorophyll, the absorption is favored by acid terronous. Its deficiency can manifest itself with yellow and white spots on the leaves and woodiness of the new shoots. Not being a very mobile element we could find these symptoms especially on the apical leaves.
Zinc (Zn): This substance is used to form seeds. Its deficiency can occur on fruit plants with leaf changes and large yellowish areas or rosette clusters of leaves.
copper (Cu): it is a constituent of different enzymes necessary for the regulation of the vital processes of the plant, moreover, together with iron, it participates in the production of chlorophyll. Its deficiency can manifest itself in stains and leaf yellowing.
Molybdenum (Mo): this substance participates in the growth and development of the plant. It is mainly used by legumes and its deficiency can manifest itself in reduced plant growth, leaf yellowing, deformation and finally withering.
Usually fertilisation takes place in two phases: during the growing season and during the resting season.
During the vegetative phase (spring and autumn) it is preferable to fertilize with a solution with a high nitrogen content and a low phosphorus and potassium content (e.g. NPK 10-5-5) in order to favour the green development; in winter, instead, it is advisable to use solutions with a low nitrogen content and a high phosphorus and potassium content (e.g. NPK 3-9-9) in order to favour the lignification and the flowering. It is not recommended to fertilize in July and August.
We can divide the fertilizers into two classes, solid and liquid. Solid fertilisers are called slow release fertilisers, i.e. the nutrients are released slowly and constantly. Usually this type of fertilizer lasts 2-3 months, they are small cubes that are placed on the soil, with the watering will begin to dissolve releasing all the nutrients.
The liquid fertilizer has a faster but shorter effect, usually diluted in water and administered with watering. If you choose to use liquid fertilisers, the interval between each application should be about 15 days.