Why do we fertilise and with what? Where do we place fertiliser and what is the most effective NPK mix available? What other methods can we use? It is not simply a case of placing fertiliser on the soil without thinking. The amount and type of fertiliser, as well as its timing depends on the species and stage of development the tree has reached. If you keep that in mind the effectiveness of fertilising increases dramatic.
Fertiliser cake techniques
Fish emulsion (NPK: 5-2-2) is the gentlest of all bonsai food mixes. What does it do? It will help produce healthy plants with sturdy stems and strong root systems. It will also assist flower production and glossy foliage. Suitable as spring fertiliser and very suitable for azaleas.
Other fertilising methods
Bio-Green is a 100% organic bio stimulant that can be applied combined with other bonsai fertilizers. Produced from 100% seaweed it contains trace elements, minerals, enzymes, plant growth hormones and amino acids. A fine feast for your bonsai because it will give foliage more colour and increases the resistance to diseases.
The reason for fertilising
Plants require 16 chemical elements for healthy growth. These include Oxygen, Carbon and Hydrogen. The other thirteen elements are absorbed through the roots, the three most important of which are Nitrogen, Phosphorus and Potassium.
In normal circumstances, all of these elements can be found in the soil a plant grows in, but in the case of bonsai, the amount in the soil contained within the pot is quickly used up and additional elements must be added. This is the reason for giving fertiliser to the tree, adding the essential elements from outside the soil contained within the pot.
Nitrogen is the main element used in the production of proteins and amino acids, vital for chlorophyll which is used to produce energy through photosynthesis. Nitrogen assists the tree with ‘green’ growth; it adds colour to foliage and fuels extension.
Phosphorus is used for the production of nucleic acid and phospholipids used in the storage of energy and transmission processes. It is also known as the flowering element as it helps with flowering and fruiting trees.
Potassium is used for production of starch, proteins and the transport of sugars. It is a vital element in the immune system, helping to ward off disease. Insufficient Potassium causes a lack of root development, poor foliage colour and a weak tree susceptible to disease and insects. In addition to the main three, smaller amounts of trace elements
are necessary for healthy growth; Magnesium, Calcium and Sulphur as well as Manganese, Iron, Boron, Zinc, Molybdenum, Copper and Chlorine. All of them have a small, but essential part to play in the growth and health of plants and a deficiency should be avoided.
Maintaining the surface soil
As the fertiliser cakes are watered, they begin to break down and melt into the soil. The fertiliser percolates into the soil and the top layer in contact with the solid cake begins to harden and stops penetration of both water and oxygen. This is particularly true with trees that have not been transplanted in a number of years and the fertiliser has created a cake of hardened surface soil. To stop this from happening and affecting the tree, clean up the hardened soil each time you change the fertiliser cakes and, if necessary, replace with fresh soil to maintain a suitable flow of both oxygen and water.
Bonsai fertiliser is more expensive than your average garden centre fertiliser as the quality is much higher and it is designed not to break up to easily and clog up the soil.
When spring comes, start slowly. After summer, build up the quantity
From spring the growth cycle starts with bud break, followed by extension and opening of leaves until the growth finishes and hardens off. During this time, stored energy is used to fuel the growth. In general, the extension continues until July, after which the tree slows down growth and begins to recoup energy expended in the earlier growth spurt. It also focuses on hardening the foliage and creating fruit, for example. During the height of mid-summer, however, when the average temperature is over 35C / 95F, the growth stops and the tree maintains itself. After this period, the tree begins to thicken and the branches lignify.
Spring fertilising is designed to create extension of shoots. Fertilising in the autumn is designed to increase thickening and structural strength. The energy used in the spring is energy that is produced and stored during the preceding autumn.
If excessive fertiliser is given in the spring more growth and extension than is required will then occur, causing long internode length in deciduous trees, or coarse foliage growth in conifers. Consider the stage of development of the tree and adjust the amount of spring fertilising accordingly. In order to create a heavily fruiting tree or thicken branches and the trunk, heavy fertiliser in the autumn is required.
Not against the roots
PK fertiliser is Nitrogen free (NPK 0 -10 -10) and will coach trees to toughen up for winter as it stimulates trunk and branch thickening and even improves the root system. You can have it both ways: as both foliar and soil fertiliser.
Deciduous tree still in training
This tree will be defoliated two or three times per year in order to speed up the ramification and so early and relatively heavy fertilisation is required. As soon as the finished image is achieved fertilisation can be reduced to less than half the amount.
Heavy fertilising when drainage is good
The picture shows the use of a colander instead of a bonsai pot and the soil is mainly grit. Both improve the drainage so that a lot of fertiliser can be given without fear of excess build up or a deterioration in water and oxygen penetration. In this case, ten times the amount of fertiliser can be given without fear of damage.
This is a particularly effective technique for the rapid thickening of trees and in particular the development of shohin trees. This amount of fertiliser will cause serious problems in a traditional pot; however, in this case the increased drainage helps.