Effective Bonsai Water Management How to Water Bonsai Trees.

The essential elements a plant needs to produce food are light and water, along with CO2, which is readily available in the atmosphere. The primary cause for the failure of many bonsai plants often stems from the inadequate management of one or both of these factors.

Managing Bonsai’s water is directly related to the capacity of the growing medium to regulate water and air availability. Ensuring that soil has at least a six percent oxygen content while remaining damp in a 4-inch deep pot over an extended time is an art.

Nothing strengthens the human/plant relationship more than keeping your Bonsai hydrated without drowning.

It is an acquired art that requires you to be attentive to your plant’s needs and respond appropriately.

Developing the feel for each plant’s needs is informed by science but relies on your perceptiveness.

Spraying Bonsai Tree Foliage With Water
Spraying Bonsai Tree Foilage With Water

Let’s take the Chinese Hackberry (Celtis sinensis) as an example; it requires soil that drains well, is moist, is occasionally wet, and occasionally dry.

That’s what the science says. The bonsai growers wanting to grow this rapidly growing deciduous tree must pay attention.

You will undoubtedly find many articles about Bonsai watering online, which may become additional.

However, if you start paying better attention to your future watering habits due to this article, I will have achieved what I hope to.


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Water’s Role in Basic Plant Biology

Water serves many critical functions in all living organisms. Water plays a pivotal role in photosynthesis in plants and serves as a transport vehicle for mineral salts (ions) and carbohydrates. Water also plays other roles in your plant’s life:

Water as a Constituent

80–90% of the fresh weight of herbaceous plants and more than 59% of the fresh weight of woody plants are made up of water.

Water as a Solvent

More compounds dissolve in water than any other substance, making it the universal solvent. As a result, water serves as the medium in which biological reactants are dissolved in cells for chemical reactions.

Water as a Reactant

In the biochemical reactions of the cell, water is a reactant. One of these processes is photosynthesis, where water provides hydrogen protons necessary for producing ATP [adenosine triphosphate] and electrons ultimately used to reduce carbon to a carbohydrate. Water also contributes to the oxygen that is produced during photosynthesis.

Water is also a reactant in the hydrolysis of plant food reserves like starch. Water molecules are injected between the glucose units of the starch polymer during starch hydrolysis, converting starch to sugar.

Water as Essential Transport

Water circulation carries the minerals from the soil across the root, up the stem, and throughout the plant. Carbohydrates, which develop in photosynthesis, are also distributed through the plant by water.

In the growing medium, plant roots create a branching network, and the ends of the youngest roots are responsible for water and mineral salt uptake.

These root hairs are located directly behind the tips of root branches, developing as the outer layer of the root’s cells becomes longer, increasing the surface area for absorption (by osmosis) of the soil’s available mineral and water content.

Watering The Bonsai Soil With a Watering Can
Watering The Bonsai Soil With a Watering Can

Water as a Component of Growth

Small cavities (vacuoles) form during cell division, absorbing water that transports mineral deposits. As the water diffuses into the tiny vacuoles, it creates pressure inside the cell, causing them to expand and increase.

As the cells mature, they no longer grow but maintain water pressure inside as the vacuoles merge and unite into a central vacuole. The walls get so thick that they lose elasticity.

Water and Turgidity

Water pressure against mature cells’ interior helps keep their form. If the pressure is lost (for example, due to excessive evaporation, mortality, or exposure to salt solutions), the cells may lose their turgidity and become flaccid.

Many tissues, such as leaves and annual plants without lignin or other reinforcing components, take their shape from the turgidity of cells.

Water and the Plant’s Thermal Stability

Water requires more heat energy to raise its temperature than other common substances. Because of this, plants, composed primarily of water, may absorb a large quantity of heat (such as from sunshine) while slowly increasing in temperature.

Similarly, the same number of calories must be wasted to drop the water temperature (for a plant), allowing plant temperature to stay close to air temperature during brief cold spells.

The high water content in a plant helps aid temperature stability while air temperatures fluctuate.

Specific Challenges to Bonsai Watering

Several factors unique to Bonsai affect the plant’s water management dynamics. Essentially, the art of Bonsai, or plant growth stunting, requires foliage removal and root management, and both foliage and roots directly affect the plant’s water usage.

Bonsai Root Management
Bonsai Root Management

Contrary to popular assumptions, Bonsai water management is unique for every season and development stage of every plant. Bonsai apprentices are known to study watering for three years. The general enthusiast, then, requires patient dedication to get it right.

The following markers may help you better understand your plant’s watering needs.

Bonsai Tree Species

Every tree family has its unique water availability requirements. A Swamp Cypress, for example, can grow with its roots partially submerged in a bowl of water, but a pine cannot.

Don’t practice blanket, blind, or routine watering; be aware of the species you are growing and water according to their needs.

Bonsai Repotting and Root Trimming

Repotting includes removing most of the hair roots, which we saw above, responsible for the plant’s nutrient and water supply.

These tiny roots are essential for your plant’s health, but dry conditions trigger their development.

Imagine the leaves sending signals to the roots for water supply, but the water collectors have been culled. Solution: grow new roots.

The speed and extent of that root growth are products of water availability. They grow to seek water in dry spells, and there is no need for further growth in wet spells.

Refined Bonsai with Good Water management
Refined Bonsai with Good Water management

Therefore, you must increase dry spells to help your bonsai tree re-establish itself. You will notice that water applications cause the soil to remain wet for longer after transplanting.

The lingering wetness is not a factor of the changed growing medium but rather because the plant cannot access the provided water.

When you repot a tree, many of the roots used by the tree to take up water will now be missing. It stands to reason that the tree should receive less water until it has settled and issued new root hairs.

Combined with a very open or fast-draining growing medium, root hairs will have plenty of oxygen and develop rapidly to seek water.

Bonsai Growth Phase and Water Management

Watering needs to be adjusted, both the initiate and maintain seasonal growth. During the growing season, the plant needs more water, which must be given less water during winter to support its dormancy.

In autumn, the plant needs water to build reserves for spring growth. October is the month of water reduction regimes.

Controlling the amount of water Bonsai require
Controlling the amount of water Bonsai require

Bonsai Growing Medium and Water Management

Your choice of growing medium is critical for all water management elements. Every tree requires good drainage but varies in its water retention needs.

Including organic material in your growing medium reduces the watering frequency, and pure LECA, expanded shale, or pumice requires more frequent water applications.

Bonsai Tree Location

If you have a bonsai tree on a cement balcony that receives afternoon sun and steady wind, your tree will need far more water than a tree under shade netting in a sheltered spot in their garden bordered with hedges.

Trees, like us, remain cool by water evaporation. The heat required for evaporation is extracted from surrounding environments, causing these to cool. Darker materials absorb light and heat and reduce the area’s relative humidity, increasing the tree’s moisture loss.

Watering Requirements Change Depending On Placement Of Bonsai Trees
Watering Requirements Change Depending On Placement Of Bonsai Trees

However, a cool micro-climate formed by shade netting, organic mulches around the floors close to your benches, and growing hedges will provide a much less harsh environment for the tree and will likely require less water.

Indoor Bonsai placed on the window sill in the heat of the day or in an AC room will lose water faster. Every little factor affects the plant’s need for water.

Bonsai Development Stage and Water Needs

More water will probably be required if the tree is young, developing quickly, and prepared for styling, especially if fertilizer is used. Conversely, withholding water is one technique that can be used to control needle length in Japanese white pines.

Bonsai Water Needs During Defoliation

A tree without leaves will use far less water than one with a dense canopy of leaves. Adjust your watering for these trees accordingly, and do not simply continue with the same routine you had before.

Simplify Gardening Bonsai Watering Tip

When a Bonsai is close to completion, with dense ramifications, and you want its growth to slow down, maintain a wetter growing medium to reduce root hair formation.

Water the tree less to hasten root hair formation (nutrient absorption potential).

Signs Your Bonsai is Getting Insufficient Water

Yellowing and wilting leaves or even dried leaves near the bottom of the tree is a sign of water deficiency. In advanced cases, some branches will have died.

Bonsai Tree With Lack of Water
Bonsai Tree With Lack of Water

Depending on your growing medium, some materials such as peat, milled bark, and similar organic materials are extremely difficult to wet should they dry beyond a point, becoming hydrophobic. An alternative is coconut coir.

Note that Japanese maples, especially the lace-leafed varieties, are susceptible to damage caused by insufficient water, exacerbated by windy conditions.

Signs That Your Bonsai is Getting Drowning – Excessive Watering

Below is a list of signs that your Bonsai is being overwatered.

  • Liverwort proliferates on the surface of your growing media.
  • In particular, conifers foliage has dull needles and scales.
  • Foliage that is smaller, yellow, or sparse.
  • Trees with thin, typically smooth bark will appear wrinkly.
  • Leaves are wilted, although the growing media is moist.
  • Dieback of branches for inexplicable reasons.
  • You discover dead, withering, and squishy roots during repotting.
  • Roots are fragile, break easily, and are “mushy.”
  • The delicate bark that protects the roots is rotting on the inside.
Signs of overwatering  a bonsai tree
Signs of overwatering a bonsai tree

Bonsai Watering Timing

Medium Dryness

A rule of thumb is to only water when the top half-inch of the growing medium is dry upon finger insertion.

If you are using a very organic mix, rub some of the media between your fingers or even insert your finger slightly into the medium; it should be relatively dry before the next water application. Any medium should never become completely dry.

Time of Day

I know it’s off the topic, but when watering turf grass, do it in the early morning to allow the grass to dry in the midday sun, reducing the opportunity to spread pathogens.

This does not apply to Bosai, which is best-watered mid-afternoon.

Watering around midday allows any water which may have landed on the foliage to dry completely by evening and ensures the addition of water when plants are losing it most.

Of course, you must find a time that suits your lifestyle. If you’re generally not around to water in the middle of the day, then the morning is preferable – for the same reasons as turf watering in the morning.

Ways to Water Your Bonsai

Like with all plants grown in containers, two methods are generally used. While piped irrigation is an option, I’m not covering it in this article as those that use it hopefully do so using moisture detection systems that trigger the supply.

Watering by Hand

Watering cans are offered in various sizes, styles, and materials. You have two options for watering plants: an inexpensive plastic watering can or a Japanese Bonsai copper watering can.

Whichever watering can you use, it should be easy to transport and pour water from. Additionally, it must have a tiny spray that won’t damage the growing medium in your bonsai pots and shouldn’t spill everywhere.

Watering Bonsai by Hand With a Watering Can

I prefer to water plants by hand using a wand. Unlike an automated system, the method encourages me to interact with my trees daily, allowing me to spot drainage issues or pests immediately.

I can also modify my watering to the tree’s demands; for example, I would water the tree less if I had just defoliated it. All these factors are considered as I move through the water and react appropriately.

It is preferable to water at least twice, moving on to the next tree before repeating the process with the first to ensure that water drains from the drainage holes.

Before it is fair to declare that it has been watered sufficiently, deeper pots or compressed root balls, especially those growing in an old media, may require a few more passes.

Watering Bonsai Trees With a Hose Wand
Watering Bonsai Trees With a Hose Wand

Watering by Immersion

Since many regions are experiencing droughts, immersion may be the ideal approach for you if you only have a few trees. This method is also incredibly water-wise; you only need a water-suitable container.

  1. Dip the entire tree into the container so the water drenches the whole pot.
  2. If the growing material is very dry, you may submerge the container in water for a few minutes.
  3. Notice the air bubbles rising to the water’s surface. When you raise the container out of the water, the old air will be replaced by new air, which benefits the roots greatly.
  4. The Bonsai can be placed on a grid that has been placed over the container, allowing any extra water to drip back into the container. You can keep utilizing this water by topping it off every few days. Alternately, the container can occasionally be emptied and the water replenished.

As I previously indicated, this is an appealing choice if you only have a few trees; you can use the kitchen sink!

The issue is that using this strategy to water your trees daily or frequently would be exhausting if you have many trees or if the trees you do have are enormous.

Choosing the Best Water Source for Your Bonsai


This form of water is arguably the best to use on Bonsai. Suppose you have some space for the necessary tanks. In that case, this water is free to collect, and your utility bill will decrease as you use less municipal water.

How much water can be gathered from the typical household roof is incredible. It can last several months (depending on storage capacity, how much water is collected, and how it is used).

Distilled Water

Distilled water is steam condensation and is available from pharmacies and other establishments. If you have even a few trees, especially ones bigger than a mame, I think it will be prohibitively expensive.

This water is essentially pure and stripped of everything, so I am not sure what the long-term effect is on the functions of a plant.

Filter Purified Water

Filtered water has been put through a membrane or cartridge filter to eliminate odor, silt, salts, and bacteria.

Different filtering levels exist, from the widely used residential under-counter type filters to the more complex Reverse Osmosis (RO) systems.

It would be best to investigate your water, preferably by having a cheap lab test done on it, and then figure out which filter system you require to get the water up to irrigation requirements.

If RO is not your only choice, I would suggest against using it because it completely purges the water and uses a lot of water to backwash the filters, which is a wasteful operation.

Some cartridges claim to have remineralizing qualities, but I don’t know enough about them to remark on how they would affect plant development.

Tap water

Tap water quality varies geographically, and municipal burst pipes or other reasons can sometimes hamper supply.

It’s probably the most commonly used water type among bonsai growers as it is generally accessible.

If you suspect the water to be very high in chlorine, fill a large vessel, and allow it to stand overnight before watering your trees.

You can speed up the process by aerating it or using an active carbon filter, and this filter will remove the chlorine and other chemicals from the water.  

The Effect Of Salts on Your Bonsai

High salt concentrations can burn or yellowish your plants’ leaves; particularly high concentrations can appear as white crystalline deposits on your pots.

Most species require low salt concentrations, which will encourage healthy growth in the tree. Using water with a high salt concentration can harm some species sensitive to salt, such as some junipers.

Frequently Asked Questions

How often should you water your bonsai tree?

The watering of Bonsai trees depends on the time of year, whether the tree is dormant, the tree’s placement, and the tree’s size. A check should be performed every seven days, and water, if required.

Can you overwater a bonsai tree?

It is possible to overwater your bonsai tree. Look for signs of yellowing foliage and shriveled leaves. If you spot these, lift the tree from its pot and check for root rot, as overwatering will starve the root system of oxygen, which can kill the tree if not altered.

Should I mist my bonsai tree?

Bonsai Trees benefit from being misted, especially if grown indoors. Heating and air conditioning in your home can dry out the foliage and cause untold damage to your tree. Misting raises the humidity around the tree preventing damage to the tree leaf structures.

Can I water my Bonsai with tap water?

Although you can water your Bonsai with tap water, it is much better to use rainwater. If you use tap water, leave it to stand for 24 hours for the chlorine and chloramine to dissipate. Also, be mindful of hard water that can leave salts in your soil and affect its pH.

How long do you soak a Bonsai tree?

When watering a bonsai with the soaking method, submerge the tree for at least five minutes. Keep the tree submerged until you stop seeing bubbles popping at the surface. This indicates that the soil is saturated. Remove the tree and allow it to drain.

Wrapping up Bonsai Watering

I made every effort to keep this article brief and to the point, but this is an essential component of successfully growing Bonsai, so I tried to cover every aspect.

However, if you have learned something, I’m happy. My goal has been accomplished if you now pay closer attention to your bonsai tree’s water needs and not just water it regularly.

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