How to care for a bonsai?

What is a bonsai?

Bonsai is far more than a simple indoor or outdoor potted plant. It is a genuine Japanese art, a form of expression of nature on a reduced scale. Bonsais are cultivated from young plants of ordinary trees, carefully pruned and shaped to acquire an appearance of maturity and striking beauty. These small trees are often endowed with deep cultural and spiritual significance, representing harmony, balance and the connection between people and nature.

Guidelines to follow are general guidelines, but each species has its own particularities, and it is very important to refer also to the specific instructions.

On the other hand, even though bonsai are very beautiful and attractive in garden centres, do not buy them on impulse. Do your homework on the species you have set your heart on and be aware of the initial investment.

One final point before we begin: inspect the plant before buying to check that there are no parasites lingering.

Indoor bonsai

There are varieties of bonsai suited to growing indoors and outdoors. Indoor bonsai are a relatively recent invention, not Japanese, made to meet market demand. Remember that bonsai are, above all, trees! Only a few species can thrive indoors with heating year-round. Humidity conditions will likely be insufficient, so prepare to provide attentive care.

Indoor bonsai that can be grown year-round, though fewer in number, are subtropical species. They prefer warm and humid environments.

These are:

• Ficus.
• The Jade Plant, Crassula or Portulacaria.
• The Chinese Elm, i.e. Ulmus parviflora.
• The tea tree, i.e. Ehretia microphylla also known as Carmona retusa.

The Ficus is the easiest species to grow, ideal for beginners or those who do not seek difficulty. Crassula comes next, it is ideal for those who do not want to devote too much time. The Elm and the Carmona are much more demanding and difficult to succeed with indoors.

All indoor bonsai can be grown like outdoor bonsai, but the reverse is obviously not possible.

Outdoor bonsai

A wider variety of tree species can be grown as outdoor bonsai. Outdoor bonsai include species such as pine, maple or juniper. These specimens require distinct seasons, with a winter dormancy period, in a frost-free and unheated location, then a growth season that takes place outside, on a balcony, a terrace or in a garden. Choose an outdoor bonsai only if you can provide these conditions.

A beautiful outdoor bonsai in bloom. There are more species and a greater range of varieties among outdoor bonsai (flowering species, colourful foliage)

What is the common care required by all bonsai trees?

Bonsai requires specific care, unlike your houseplants. It should not be planted in a deep pot with potting soil for houseplants, and its substrate should allow maximum root aeration.

How should bonsai be watered?

Watering bonsai is highly specific and crucial. As its substrate resembles small pebbles that do not cling to the roots, it requires frequent watering, without fail. The more well-drained the substrate, the more water the plant needs.

Water it generously, outdoors or in a sink, where the water can drain away without issue and without fear of making a mess. A hose-end nozzle or a shower head is ideal, and we should not fear watering the foliage; on the contrary.

A second thorough watering should be carried out a few minutes later.

When drainage is complete, we can return it to its place.

Water bonsai generously with a hose-end nozzle or shower head

How to repot a bonsai?

Bonsai should be repotted every two to three years (sometimes one year for the most vigorous species) to ensure a healthy root system and allow optimal growth. Carry out the repotting at the start of spring before growth resumes. You should repot when you observe the roots growing in a circle around the plant. If not, wait another year.

Use a well-drained, bonsai-specific mix to prevent root rot. Two options are possible:

• We can find bonsai soils based on peat, pine bark, pumice and loam, which are often the choice of beginners or less demanding species.
• Bonsai enthusiasts make up their own mix based on volcanic rock, clay and organic material such as pine bark, with no soil or potting soil at all. This second type of substrate promotes optimal root aeration and eliminates any risk of root rot.

During repotting, prune the roots of the miniature tree to limit its growth and leave space in the pot. Once the root ball is disentangled, remove about one third of the substrate and roots by reducing the size of the largest roots to favour the growth of rootlets, better able to absorb water and nutrients.

Thus, during repotting, you do not necessarily change the pot size, but you renew the substrate and take the opportunity to prune the roots.

How to prune a bonsai?

Pruning is an essential step to keep a bonsai healthy and achieve balanced growth. Make light but fairly frequent prunings to maintain the desired shape and encourage compact growth. Dead or weak branches should be removed to promote new shoots. Trim shoots to four or five leaves with a very sharp pair of scissors to bring them back to the three- or four-leaf stage. Outdoor bonsai grow more quickly than indoor bonsai.

To shape the bonsai, we practise wiring, which involves attaching and gently wrapping aluminium or copper wire around the branches and trunk. The main aim of wiring is to control growth and the direction of the branches, creating artistic and aesthetic shapes that evoke the size and form of mature trees in nature.

The pruning and wiring are a patient craft and a true art form.

An outdoor pine bonsai in its mineral substrate, trimmed with scissors

How to care for an indoor bonsai?

What is the best location and light exposure for indoor bonsai?

Indoor bonsai thrive in well-lit environments, but not with permanent direct exposure to the scorching sun. Place them near a very well-lit window. A bonsai needs bright light and possibly a few hours of sun if it is morning sun or late afternoon sun. Be vigilant about temperature fluctuations and draughts, as this can affect the health of your houseplants.

How to water an indoor bonsai correctly?

Watering is crucial for indoor bonsai. It is essential to maintain a constant moisture level in the growing medium, without allowing the roots to sit in water. Regularly check the moisture of the substrate and water as soon as the top layer begins to dry. Mist the leaves with soft water also helps to maintain ambient humidity. Bonsai trees appreciate it. You can also place them on a tray filled with water.

An indoor Ficus bonsai that enjoys misting its leaves

What fertiliser for indoor bonsai?

Potted indoor plants, and bonsai in particular, require regular nutrient supplies, because frequent watering leaches nutrients. Use a balanced fertiliser in liquid form specially formulated for bonsai. Add the fertiliser during the active growth period, usually in spring and summer, but avoid applying it when the plant is in dormancy. Pour it into the irrigation water every 15 days during the growing period.

What are the common problems of indoor bonsai?

If your bonsai loses its leaves, it is most often due to a location not bright enough or to improper watering, but some species naturally shed their leaves in autumn. Common problems of indoor bonsai include pest attacks such as aphids and scale, as well as fungal diseases. Inspect your plant regularly and act quickly to isolate and treat problems as soon as they appear.

How to look after an outdoor bonsai?

Outdoor bonsai species require a winter dormancy period, carried out in a frost-free and unheated room. During the growth period, they are placed outdoors.

What is the best location and light exposure for outdoor bonsai?

Outdoor bonsai require direct sunlight to thrive. Place them in a sunny spot in your garden or on your terrace, ensuring they receive at least six hours of sun per day. Rotate the pot regularly to ensure even growth.

How to water an outdoor bonsai properly?

Watering is also crucial for outdoor bonsai, as they can dry out more quickly due to sun exposure and wind. Check the soil moisture frequently and water thoroughly when the top layer becomes dry. Use a drip tray under the pot to retain excess water and maintain a constant humidity around the plant. In hot, dry summer periods, an outdoor bonsai may need to be watered up to twice a day. In intermediate periods, usually once a day, and in winter, hardly at all, about once every two or three weeks.

What fertilisation for outdoor bonsai?

Outdoor bonsai, for the reasons mentioned in the previous section, quickly deplete soil nutrients. Use a fertiliser specially formulated for bonsai, rich in potassium, phosphorus and nitrogen, to support healthy growth. Apply the fertiliser evenly throughout the active growth season.

What are the common problems with outdoor bonsai?

They are also susceptible to parasitic attacks and fungal diseases. However, regarding parasites, outdoor plants are more exposed, they also encounter beneficial insects, unlike indoor plants. Many problems can be treated with natural solutions, such as black soap to combat aphids and scale insects, for example, or the essential oils.