In my last letter I committed the imprudence of promising an article about the fertilization of bonsai. In order to center the shot I asked Professor Google in Spanish about "bonsai fertilization": 63,100 results. In case they were insufficient I searched in English "bonsai fertilization": 273,000 results. Decidedly the world of bonsai does not need my technical contribution on this subject because among all these articles there are already some good; who at this point does not already have his own theory about the best fertilizer system has a choice of information.
I have a habit of fulfilling what I promise, but what to do this time? Well, I am going to tell you where many years of trial and error have taken me and, as a bonus, I give the opportunity to whoever wants to criticize me publicly, which will undoubtedly allow me to continue learning.
For practical reasons, I did not start as many bonsai pioneers preparing my solid fertilizer mixtures. After all, there were already available pellets of all kinds, of domestic origin, and good brands imported directly from Japan. I immediately gave up the first because although they were cheap, they formed a paste that quickly clogged the substrate; I scratched my pocket and tried the best of the best, straight from Japan, because my trees were worth it. He who wants to know the wonders that works in our bonsai any fertilizer has only to read the information of its manufacturer; to know their disadvantages it is necessary to use them because they don't talk about that. I stopped using the best of the best, straight from Japan, because I did nothing but fill and empty fertilizer baskets every month (better not mention the work involved if you use tea bags) and frankly I had better things to do with my time.
I started using slow-release mineral fertilizer. They are NPK balls, with micro-elements, covered with a permeable membrane that releases nutrients whener you water your trees. There are different proportions of NPK and duration up to nine months, which allows a single application in spring, distributing the balls on the surface of the pot (no, it is not necessary to bury them), and eliminating them in autumn. In my opinion, this is the best base fertilizer for amateurs, occasionally supplemented with liquid organic fertilizer. But when several thousand trees are grown as is the case at Hatoen it is necessary to simplify and that is why I now use mineral and organic liquid fertilizer, which I provide alternately once a week from April to October with the irrigation water.
As a mineral fertilizer, in spring and summer I prefer a 20:20:20, of those used in hydroponic cultivation, because it has less non-assimilable salts than the less rich, and the accumulation of salts in the substrate is undesirable. Also being richer allows you to reduce concentration; low concentration and high frequency are always preferable, hence my previous recommendation on slow-release fertilizers. From September onwards I replace it with another one with a lower proportion of nitrogen to prepare the plants for winter.
Nitrogen is critical to regulate growth, hence a mature tree needs less than one in formation, and also influences the resistance of plants to diseases: a plant that lacks nitrogen is more resistant than other grown with excess. The secret is the balance, neither too much nor too little, to take advantage of the normal growth of the plant without making it a sickly obese. Potassium and phosphorus may be in excess, the plant will only take what it needs without serious contraindications.
Among the organic fertilizers that I use on alternate weeks with the mineral are:
- Humic and fulvic acids, which combine with the clays of the substrate increasing the retention of fertilizer cations, and have a bio-stimulating effect on the roots.
- Rooting stimulant
- Sprouting and growth stimulant
- Anti stress during strong heat waves.
Periodically I use a foliar bio-stimulant based on amino acids for its rapid effect in stressful situations.
Do not overestimate the effect of fertilizer, it only serves healthy and growing plants and therefore should not be given to weak or newly transplanted plants. Other factors such as lighting, temperature, irrigation, or aeration of the substrate are more important for plant health than the fertilizer itself.