Bonsai Fertilizer

Bonsai fertilizer is a vital factor in successful bonsai growing.

Like many people, I used to believe that fertilizer is food for bonsai trees. After study, however, I figure out that my belief is not precisely true. Fertilizer is much more similar to vitamins rather than nutrients.

The real food for plants is carbon dioxide and water, which are converted to sugars and carbohydrates through photosynthesis process. Fertilizer acts as assistance for such biological process of food production in plants.

Fertilizer Components

Three basic elements of any fertilizer are Nitrogen (N), Phosphorus (P), and Potassium (K). Each of them serves different purposes.

  • Nitrogen is major component of proteins, hormones, chlorophyll, vitamins and enzymes essential for plant life. Nitrogen metabolism is a major factor in stem and leaf growth (vegetative growth). Too much nitrogen can delay or prevent flowering, while deficiencies can cause yellowing of the leaves and stunted growth.
  • Phosphorus is necessary for photosynthesis, protein formation and almost all aspects of growth and metabolism. It is essential for flowering. Phosphorus deficiency - sometimes associated with purple leaves - results in slow growth, poor flower production or premature loss of flowers.
  • Potassium is necessary for the formation of sugars, starches, carbohydrates, for protein synthesis and cell division in plants. It helps to control water absorption and loss, improves the physical sturdiness and cold hardiness of your plants, and enhances flower color. Too little potassium can result in mottled, spotted or curled leaves, or a burned look to the leaves.

When to fertilize Bonsai?

Fertilize during the entire growth season of the tree; from early spring till mid autumn. Indoor trees can be fertilized around the year. Although sometimes disputed, do not fertilize repotted trees for about a month; also do not fertilize sick trees.

How to choose fertilizer?

On each bag of fertilizer, there is a ratio, such as 10-20-10 or 29-6-4. Do you know the meaning of those numbers? Well, they indicate the percentage by weight of three major components, which are Nitrogen (N), Phosphorus (P), and Potassium (K).

Yet, the "N-P-K" values are not reported in a straightforward manner, but in terms of their correlative compounds: Nitrogen (N), phosphate (P2O5), and soluble potash (K2O). Then, a 10-20-10 fertilizer has 10% nitrogen, 20% available phosphate (P2O5) and 10% soluble potash (K2O).

Different ratios of N-P-K are being used for different trees at different times of year, which is very important to take into account when fertilizing Bonsai. In most cases, you will want the fertilizer with the highest first number, the fertilizer that contains the highest percentage of nitrogen, such as a 24-8-4.

A bag of bonsai fertilizer that only has two numbers, such as 20-0-20, or one number, such as 34-0-0, is an incomplete fertilizer because it is missing one or two of the three major elements.

To promote good flower or fruit production, use a fertilizer with the middle number higher than the first. If you want to toughen up your plants for better drought, disease, or winter resistance, use a fertilizer with the last number being the highest.

Using Fertilizers Properly

You can fertilize by watering directly to the soil or by applying directly to the leaves. Never feed a bonsai tree if the soil is dry. It is recommended to first water with straight, clean water. After 10-20 minutes, you may water again with fertilizer diluted in water.

You can put the bonsai fertilizer in a spray bottle because the foliage can absorb the fertilizer, but bear in mind that the effect is more rapid evaporation. It is very important to regularly change the method of application, or the roots may become weakened if we just spray the leaves all the time.

Tips for fertilizing

  • Do not fertilize a bonsai tree during the winter months, or right after repotting.
  • Make sure you thoroughly water your bonsai before fertilizing and be careful to never fertilize it while dry.
  • If your tree is unhealthy, do not mistake fertilizer for medicine. Instead, avoid fertilizing it until it becomes healthy again.
  • Switch brands of bonsai fertilizer regularly as they all have different concentrations of certain minerals and trace elements. It is beneficial for the growth and health of your bonsai to be exposed to differing amount of these minerals and trace elements.
  • Follow the directions on the fertilizer and avoid over-fertilizing your bonsai. Fertilizer is good for your bonsai, however, too much fertilizer can be bad for it.
  • The timing of the application of bonsai fertilizers is very important. Too much fertilizer, or applying it at the wrong time can lead to an over abundance of foliage, delayed flowering, leaf and root burn, or even plant death due to excess fertilizer!

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