How To Make A Bonsai Trunk Thicker

Bonsai is a hobby known for its ability to elicit feelings of tranquility and harmony with nature. However, this art form demands patience from its practitioners, and it can be frustrating when one careless mistake undoes months (or even years) of work.

Something as simple as the thickness of your plant’s trunk can have a profound effect on the shape and longevity of your bonsai.

Some of this advice may seem obvious, but there are some common mistakes that bonsai growers of all experience levels make when attempting to grow a healthy plant with a thick trunk.

Additionally, the specifics will vary depending on the plant you are growing, your local climate, and the amount of time you are willing to spend on maintenance. Keep reading to learn more about how to make a bonsai trunk thicker.

Regulate Humidity and Water Bonsai Properly

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All plants need water to live and grow; bonsai is no exception. However, the frequency and volume of water needed depends on the species, size, and age of your bonsai. 

  • Generally, the best practices for watering your potted plants is to pour over the top of its soil until it flows out of the bottom drainage holes 
  • Proper drainage is essential because it promotes airflow for the bonsai’s roots, as well as prevent salt buildup and root rot

Humidity also plays an important role in the health and thickness of a bonsai’s trunk. Too much or too little humidity can negatively impact the growth and thickness of a bonsai trunk. Ficus and maple bonsai require high humidity; juniper, baobab, Chinese elm, and pomegranate require low humidity. 

If you need to increase the humidity, then you can use a humidifier to ensure your bonsai is receiving enough moisture.

On the other hand, if you live in a tropical region where there is a lot of humidity, then a dehumidifier may be necessary if your bonsai thrives in drier conditions. In this case, you will want to invest in a dehumidifier to optimize the growth and thickness of your bonsai’s trunk. 

Provide Moderate Sunlight to Maximize Thickness

Sunlight is equally important as water to the growth of your plant by providing it energy through photosynthesis. Chinese elm, pomegranate, and baobab bonsai require a lot of exposure to sunlight, so they should be grown outdoors in a location with clear skies. 

Since sunlight is one of the primary sources of energy for bonsai, you will not be able to maximize the growth and thickness of a bonsai’s trunk unless there is enough sunlight exposure. If you are keeping your bonsai indoors, then make sure to place your bonsai in front of a window where sunlight can reach.

Juniper and Japanese maple require moderate sunlight, so they can be grown outdoors in cloudy climates. Ficus bonsai prefer indirect light, so they are best placed indoors in well-lit areas.

Use High-Quality Soil to Promote Trunk Thickness

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Picking the right soil for your bonsai can be complicated, but it will have a substantial effect on its growth and trunk thickness. Generally speaking, plants are very sensitive to these soil factors:

  • Ph balance: Some plants prefer acidic soil with a low Ph balance (6.0 or lower), others prefer alkaline soil with a high Ph (8.0 or higher), and others prefer neutral soil in the middle (between 6.0 and 8.0).
  • Salinity: Many plants will struggle to grow in soil with high salt content, but others are less susceptible and may even thrive in salty soil.
  • Density: Soil that is tightly packed can provide a stronger hold for the bonsai’s roots, but looser soil is better for airflow.
  • Water retention: Some plants require soil that stays moist for a long time in order for its roots to absorb the water. Others prefer soil with better drainage since it helps prevent root rot.

Ficus bonsai are healthiest when potted in soil with decent water retention, good airflow, low salinity, and a slightly acidic Ph balance. Juniper prefers drier soil and can handle a wide range of salinity and Ph, so these factors are less of a concern. On the other hand, maple bonsai needs moist soil with a low Ph and salinity. 

Pomegranate is resistant to high salinity and varied Ph but prefers soil with high water retention for maximum growth.

Chinese elm prefers soil with low density, good drainage, and a neutral Ph balance, such as sand or silt. Finally, baobab will thrive in sand or clay due to its high drainage, low density, and neutral Ph balance.

Use a Large Pot with Good Drainage

Whether your bonsai plant is kept indoors or outdoors, it is common to keep it in a pot. Although there are pots made specifically for keeping bonsai, growing your plant in a larger pot with good drainage is an ideal first step if you want to ensure it has a thick trunk. 

By providing a larger pot for your bonsai to grow, your plant’s roots have enough breathing room to absorb water and nutrients from the soil—although it may necessitate some root pruning or wire manipulation when transferring it to a bonsai pot. 

Once your plant has grown to your desired size and thickness, you should consider transferring it into a bonsai pot for aesthetic purposes and greater portability.

Although shallower than most traditional plant vessels, these pots are wide enough to provide radial root spacing.

This makes it tempting to grow your plant in a bonsai pot for the entire duration, but this will result in a smaller plant and runs the risk of a thinner trunk.

Bonsai Thickening Techniques

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The information listed above is not only important for bonsai, but for raising plants in general. However, there may be situations where you are unable to naturally thicken your plant’s trunk in these ways:

  • You may have received a bonsai from someone or purchased it from a store
  • You may have limited space or a less than ideal climate for plant growth
  • You may have a strict time constraint and need a thick trunk more quickly

In these cases, there are a few techniques that advanced bonsai growers use to thicken the trunks of their plants in less time. Please be cautious when attempting these tricks on your plant, since they run the risk of ruining all the work that previously went into your bonsai.

Before you think about employing any of these bonsai thickening techniques, make sure your bonsai is receiving enough sunlight, water, and nutrients. Unless your bonsai is being taken care of properly, these techniques are difficult to execute properly to maximize the thickness of your bonsai. 

Sacrificial Branches

Although the primary goal of bonsai is to shape your plant in a particular way, some growers will allow their plants to naturally grow extra branches that defy their intended design. 

The leaves from these branches will aid bonsai in photosynthesis, resulting in thicker growth at a faster pace than if they were pruned early in their development. After the plant reaches a size that is ideal for the grower, they will usually prune these branches to create their desired shape.

Are Bonsai Trees Hard To Care For might be an interesting article for you!

Nebari Development

One aesthetic feature of bonsai is nebari, which refers to visible surface roots. This is a method of buttressing the base of the plant and will greatly enhance the thickness of its trunk. 

Nebari is typically developed on bonsai grown in shallow pots because of limited space, but they can be developed in regularly potted plants or transferred plants with the aid of wires that restrict the nutrient flow to deeper roots.

This is best accomplished with plants that have already grown a bit naturally, since manipulating its roots can stunt bonsai growth and inhibit trunk thickness.

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