Fertiliser

Once in the pot, the nutritional content of the soil on its own is often not able to satisfy bonsai requirements to grow strong and healthy trees. For this very reason, bonsai enthusiasts regularly use organic or inorganic fertilisers, liquid or solid, pre-made or personally mixed depending on their preferences.

Your bonsai will need seventeen very important nutrients, which are divided into macronutrients and micronutrients. The nutrients include calcium, magnesium, zinc, and iron, to name a few, and they will be absorbed by the tree through the soil.

While the micronutrients are required in very small quantities (one part per million), and trace elements of the most important are usually contained in fertiliser products, the macronutrients are the ones that we are after. Specifically, we’re looking for nitrogen, phosphorous, and potassium. These are often highlighted on fertiliser packaging as NPK with their quantity (for example, N-P-K 4-5-4). These three macronutrients are responsible for the vigour of the tree, the colour of the leaves, the health of the roots, and the fruit and flower production, along with resistance to diseases.

It is important to choose a well-balanced fertiliser that is not too high or too low in these nutrients. Overfeeding may burn the root system or unbalance the growth of the tree and leaves, which we aim to keep at a certain size. Alternatively, there may be enough to keep the tree healthy because it will not be able to withstand the poor nutritional environment.

I personally use liquid fertiliser from spring until the end of summer and then apply solid pellets in autumn and, in some cases, winter. I look for the following proportions depending on my trees’ needs, the season, and the specimen:

  • N-P-K 6-3-6
  • N-P-K 4-5-4
  • N-P-K 5-3-5.

The feeding period commences with the start of the growing season (the end of March), and I feed at regular intervals of at least once every two weeks. The gap increases to once a month in autumn, and then I stop feeding in the winter when the tree starts its dormancy phase (except for indoor bonsai, which I continue to feed).

I hope that this guide for feeding frequency, timing, and portion gives you a starting point to approach this task. Along the way, you will make your own adjustments and improvements to suit your trees.

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Indoor Bonsai and Their Light Requirements

Keep indoors, it may be quite challenging to provide bonsai plants with the right environment, particularly regarding light, which they use for photosynthesis.

If your tree starts to weaken and the leaves turn yellow and start to fall, then it may be a sign of poor light. If the leaves begin to wither, dim in colour, drop or dry, then the tree could be getting too much light.

The length of light exposure is a factor to consider—your bonsai will need both light and dark periods each day. On average, a tree needs around twelve hours of a certain amount of light and a minimum of ten to twelve hours of darkness to help the tree to rest.

South-facing windows can usually provide bright daylight (the type of light most plants appreciate). But how close or far your plant is to the window will drastically change the amount of light it will receive—this amount is usually calculated in lux (lumens per square meter).

If you keep your bonsai indoors, it will be at a room temperature, which gives to the tree trigger to start its growing phase. But to allow your tree to photosynthesize, it will need a minimum of 2,000 lux, or the above issues may start to rise—it has the right temperature to grow but not the right amount of light.

 

You can easily check the amount of lux your bonsai receives by purchasing a little light meter to help you estimate if the tree is getting enough light or needs extra support. To make up for deficiencies, several different kinds of lights  partially or fully emulate the spectrum (rainbow band of colours) of light that the plants need to grow—fluorescents or LEDs, to name a few. The light choice is quite individual because it will be based on the type of plant collection and surface to cover.

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Repotting

Repotting is a task that every Bonsai enthusiast needs to face keep their loved tree in good health and at the right size, since no one can stop roots from growing. Repotting will need to be handled every year or two or more depending on the age, growing speed of each specific specimen and by the root mass in the pot. Check if the root mass fills the pot; it is a good habit to estimate when your Bonsai needs to be repotted. If you see that your Bonsai has pot bound, it’s time to repot or the tree will suffocate as air circulation and drainage will have been reduced by the roots drastically. To keep your tree healthy, it is important to provide new nutrients derived by fresh soil and to allow new roots to growth. To achieve this goal, we need to act on the root system by reducing part of its mass. I usually remove one centimetre from the top, one from the bottom and one from each side of the root ball with the aim to keep my tree in its original pot. This will allow enough room in the pot for new roots to grow and space for fresh soil, without stressing the tree too much. The common period to repot is usually early spring before the buds start to swell, as this will give enough time for the roots to regenerate while not requiring too much energy for foliage growth. It’s good to protect your tree for about two weeks from direct sunlight, draught and rain while the root system settles. Also, fertilising should be suspended for at least four weeks.

To approach the repotting, you will need the following material:

  • A pot
  • Pot mesh
  • Bonsai wire
  • Fresh soil mix
  • Root scissor
  • Wire cutter
  • Jin plier
  • Chop stick
  • Mallet

 

Best practise it to prepare the soil mix and the pot before working on the roots (wait for the soil to start to dry as this will make it easier to work on the root mass and the soil attached to it). Fit the meshes to the pot and some wires that you will use to anchor the tree to the pot and put a small layer of soil at the base of the pot.

Repotting media

Now work on your rootball with a chopstick and root scissor, then fit it into the pot, add the remaining soil, tap the angles of the pot to remove air pockets with the mallet, and fasten the tree using the Jin plier to the pot. Lastly, water it. Job done!

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Bonsai Soil

Soil is one of the most discussed topics among Bonsai enthusiasts and with good reason. It plays a vital role in the health of our beloved trees.

For Bonsai to survive, it needs the right amount of air, water, and nutrients. Soil, which is made up of minerals, organic matter, water, and air, is the medium that fulfils these needs.

All Bonsai enthusiasts have their own soil mix that suits their collection. But no matter what soil mix you use, they all should fulfil the following requirements:

  • Retains as much water the tree requires in the form of vapour
  • Supplies nutrients
  • Provides good drainage to prevent the roots from rotting
  • Allows air space to permit the roots so they can breath

Most Bonsai mixes are made from a combination of inorganic and organic soil to balance the Bonsai’s nutritional requirements, such as minerals (from inorganic soil) and living and dead organisms (from organic soil). Inorganic compounds tend not to breakdown, allowing air circulation and good drainage for the roots, while organic matter tends to breakdown, retaining a higher volume of moisture.

To choose the right mix, you should also consider the following:

  • Specimen: Some species require a drier environment or higher acidity than others.
  • Exposure: Will the tree be exposed to full sun, semi-shade or full shade? The level of exposure will influence the moisture levels in the pot. For example, a tree in full sun will need higher moisture in the soil because it will tend to dry faster.

Once the right mix been chosen, the moisture level can be easily amended by the soil grade. For instance, a coarse soil will retain less water and have better drainage while a fine-grade soil will stay moist for longer periods.

Here some inorganic and organic matters commonly used for Bonsai purposes:

  • Akadama: A granular, clay-like mineral often used on its own because it has great drainage and moisture-retention properties
  • Fuji Grit: a volcanic soil great for improving aeration
  • Pumice: a light and porous volcanic rock ideal for creating air space
  • Kiryu: a neutral, PH-heavy Japanese pumice resistant to frost
  • Kanuma: an acidic pumice mainly used for azaleas
  • Peat Moss: a fine organic material with high water retention
  • Bark Mulch: promotes beneficial fungi and has high water retention
  • Compost: a decomposed matter rich in nutrients with high water retention

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Choosing a Pot

Pots are an essential requirement for trees horticulturally and aesthetically.

When choosing a pot, the first consideration must be related to the horticultural needs of the Bonsai because its health should be your top priority. The pot needs holes and feet to avoid waterlog, allow for aeration, and let you anchor the tree when it needs to be re-potted.

Besides the horticultural necessities, the pot artistically plays a great role in enhancing or completing the qualities of your Bonsai. To make things more interesting, you can choose from a multitude of pots in different shapes (oval, rectangular, square, round, hexagonal, octagonal, etc.), size, colour, and glazed or unglazed. Conifers and evergreens are usually displayed in unglazed pots (red, grey, and brown) because the earthy colour highlights the green tint of those magnificent trees. Deciduous Bonsai, on the other hand, are displayed in coloured glazed pots, which balance the tree during the falling period and add some texture and shade. It’s important to avoid a perfect match between the pot and the colours the tree will show when it will bloom to avoid overpowering one or the other element and help the viewer’s eye flow harmoniously.

media pot

Another consideration to make when choosing a pot is if the tree looks strong and powerful (masculine) or delicate and elegant (feminine). Deep pots with corners, such as rectangular, square, and hexagonal pots, are usually considered to be a good match for a masculine-looking tree, making it appear well established in the ground, which accentuates the sense of power and stability. Oval and round pots are considered more suitable for feminine-looking trees because they balance the sinuosity and gentleness of them, and the shallowness emphasises the beautiful movement and makes the tree appear taller.

In the end, your Bonsai should please you first, so as long the horticultural needs are met, feel free to make the choices that best suit your taste.

Enjoy Bonsai!

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