A plant is composed of four basic elements. The first three are carbon, oxygen and hydrogen. They form a complex protein called albumine. They represent 94% of a plant composition. The other 6% are composed of 13 others elements. These are classified in two categories. The first one being the macroelements and the last being the microelements.
Principal Macro-ElementsThe first group, the macroelements, is composed of six components and must be present in greater quantities then the rest. Three (3) of them are most common and are often symbolised by “NPK”. They are :
Nitrogen will promote leaves development and give them a deep green coloration. Evergreen prefer a high nitrogen content fertilizer because of the acidity and it help keep the needles/foliage deep green. Nitrogen is the vital element of plant growth as it help compose the albumine protein.
Phosphorous will give the plant the energy it need to develop cells. It also promote amidon and glucose by accelerating the chlorophyl process. Another role of the phosporous element is to promote roots development. Strong roots are essential for plants to absorb all the mineral and water they can get. Flowering and fructification are also affected by phosphorous presence since plant tend to produce more when fed a proper portion of phosphorous. We can compare phosphorous to the plant as essential as the frame and the fondation of a house.
Potash salt control all aspect of the plant metabolism. It help prevent diseases and resist to insects by improving the quality of the plant fiber. Altough Phosphorous is essential for flowering, potash will help a plant stay strong while it produce flowers, fruits and vegetables. It also help distribute to roots, branches and leaves, the amidon and glucose produce by photosynthesis.
Other Macro-ELementsThe three last macro-elements are calcium, sulfur and magnesium. Magnesium is the most essential as it’s the principal component of the chlorophyl.
Micro-elementsThe remaining 7 of the 13 elements, are the microelements wich consist of manganese, iron, copper, boron, molubdenum, zinc and chlorine. These are present in much smaller quantities but are still necessary for the plants development.
With that being said, there is no doubt that the best fertilizer will be the one that can provide all of the previously mentionned elements. And this is what we will usually find in store. The most common fertilizer are the represented by three number, much like 20-20-20. These three numbers refer to the previously mentionned NPK elements being NN-PP-KK. You will also, find a three numbered fertilizer stating in contain oligo/micro-elements. Oligo/Micro-elements are the rest of the thirteen (13) elements mentionned. As almost all fertilizer are containing the NPK elements, but are containing different oligo/micro-elements it is best to switch fertilizer every other feeding to assure the maximum presence of macro-microelements.
I cannot write without talking about bonsai. Well bonsai are plants, but namely tree's. Same apply's for fertilizing bonsai. You must evaluate the needs of each species as they are different, but a general rule with bonsai enthusiast is to use a low content fertilizer and fertilize more often. For example, anything below 4-5 is considered low compare to the regular 20-20-20. Again each tree as it's needs, as evergreen could require more nitrogen, so something rated like 3-2-1 would be ideal. To the opposite, a flowering and fruiting species, will require more potash and phosphorous content, so a 2-4-4 would be in order.