page contents The Little Bonsai: February 2015

Growing and Caring for Bonsai Trees

Growing and Caring for Bonsai Trees

Watering Bonsai - How to water a Bonsai

Plant Watering SystemBonsai, as with nearly all other types of cultivated plant, require moisture at their roots to survive. Without a continual source of moisture, the tree is unable to continue its life process, initially losing leaves, then branches and finally the entire tree can die. Never doubt that the quickest way of killing a bonsai is to allow the compost to dry out completely.

However, though the effects of under-watering are immediate, over-watering a bonsai also causes ill-health in trees. The effects of continual over-watering takes much longer to become noticeable and can often be difficult to diagnose until parts of the Bonsai start to rotten away. Established plants and trees growing in the ground have the ability to 'adjust' to their habitat and the quantity of water that is available to them. If there is not enough water available to the root system, the roots will spread out into the soil until enough moisture can be reliably acquired. Thus plants growing in relatively dry areas will have far-reaching root systems that will continue to spread out until a reliable source of moisture can be found. On the other hand, trees growing in damp conditions where moisture is permanently available in the upper levels of the soil, will tend to have shallow root systems as they have easy access to moisture.

In the confines of a pot, a bonsai loses this ability to self-regulate its exposure to moisture. It is unable to govern how much or how little water it accesses. The compost in a bonsai pot is also far less stable than soil in the ground, its ability to dry out is greatly increased and it is greatly affected by the outside influences such as the weather and the surrounding ambient temperature. Correctly watering your bonsai is a skill itself and is not as straightforward as one might expect when first starting out. It is often said in Japan that it takes 3 years to learn to water correctly. It can sometimes take three years of tree losses before a bonsai enthusiast realises that it is his/her watering regime that might be the cause!

Bonsai Watering System

bonsai watering systemI have found this system very interesting as it can be done passively without neglecting the Bonsai. Especially if you have more than one Bonsai, this type of watering system is very useful. We all know that Bonsai need special attention. Blumats provide that but the regular ones are too long for most Bonsai containers. This one solves that problem. It can save an immense amount of watering time because this can automatically water the bonsai without needing to submerge it. In very dry areas like here in Colorado, it helps Bonsai survive those very dry days when their owners may be distracted or gone and not paying as much attention as they should.

Copper Watering Can

copper watering
This copper watering can made in Japan is the best bonsai related item I have ever purchased. It makes watering my bonsai trees a pleasure, almost a Zen experience. Kaneshin makes some of the best bonsai tools and equipment in the industry and the quality is outstanding.

This watering can is a functional peace of art. It will most likely out live me. The two rosebuds have a wonderful flow. When not in use it will be hanging on the wall for all to see. It's a classic more for professional Bonsai enthusiasts. This copper watering must be stored in-house, ideally in a greenhouse where you don't forget to water plants regularly. Below, a brief but very interesting video on how to use the copper watering can. Please always remember, if you decide to purchase this beautiful copper watering can, please handle with care! It's a piece of art!


Bonsai plants rely on a continual flow of water to stay alive and to grow. Water is absorbed from the compost into the roots by a process known as osmosis, the water is then pulled up the body of the plant and is released into the atmosphere through the foliage. This process allows the plant to distribute vital nutrients throughout its structure. However, without a source of moisture at its roots, this flow of water is interrupted and the plant structure quickly collapses and dries out. Leaves and branch tips are the first areas to be affected, followed by branches. Finally the trunk and roots themselves collapse and dry-out by which time it is unlikely that the tree will survive without damage. Application of water at this point is often too late; moisture can actually be absorbed out of the roots back into the wet compost in a process known as reverse osmosis.

As previously mentioned, the effects of over-watering a far more subtle and can take a relatively long period of time to detect. Over-watering creates an environment for the root system that is permanently wet. Roots need oxygen to 'breathe' and the presence of too much water reduces the ability of the compost to absorb air. This in turn causes the fine root hairs to suffocate and die. The immediate effect to the tree is a loss of vigour as parts of its root system are unable to grow and/or dieback.

More worryingly, the dead roots start to rot. Naturally occurring bacteria are able to colonize the dead tissue and in very wet composts are able to thrive. As the root system continues to die back from the effects of overwatering, the root-rotting bacteria are able to spread throughout the root system and slow (if not completely stop) the ability of the tree to seal the remaining live root-tips. Gradually the live portion of the root system becomes smaller and as it does it is able to support less of the visible top growth of the tree.

Foliage on the tree will start to yellow and drop; smaller branches will shrivel and die back. As the live portion of the root-ball becomes even smaller, it is eventually unable to support the primary branches and the trunk, causing the tree to die. Root-rot is often only detected at repotting time in Spring. Rotted roots will be found to be black and will disintegrate when touched. The only reliable way of stopping root-rot is to cut away all dead areas of root.


As has already been discussed, it is important to avoid the effects of under-watering and over watering. So how do you water a bonsai correctly?

auto watering system
Auto-Watering system, the smart way
Firstly, NEVER water to a routine. Simply watering on a daily basis without first observing the condition of the bonsai soil is often carried out by beginners following the advice of well-meaning bonsai retailers. Bonsai can indeed require water on a daily or even twice daily basis, particularly in hot weather or early Spring. However, watering to a routine commonly leads to permanently wet compost at other times. If the compost does not lose some of its moisture content between each watering, it means it is permanently wet, leading to problems associated with overwatering.

Instead, trees should be checked routinely (at least on a daily basis), so their water requirements can be observed and they can then be watered when they actually require it. The surface of nearly all bonsai composts change colour and appearance when it starts to dry out. With careful observation, it is always possible to tell whether or not the compost surface is dry or not. This can take anything from 12 hours to a week or longer after watering, depending on a variety of factors such as the surrounding ambient temperature, plant vigour, pot size and whether it has rained or not. In the UK for example, trees tend to need watering daily during the Summer but with lower temperatures and increased rainfall during Autumn, Winter and early Spring, watering needs can change day by day. Never assume that because it has rained your tree has received enough water particularly during the Summer. Often, it only rains enough to wet the upper layers of the compost.

The correct time to water is when the top centimetre of the compost has started to dry out. With regular observation of your trees on a daily basis, you should be able to apply water when it is actually required. Allowing the compost to dry a little between each watering will ensure that they are not overwatered.

Different trees have different water requirements, try to water individual trees in a collection as they require it, rather than en masse.

Bonsai Repot - When is the best time to repot your Bonsai

Potting is one of the most complicated subjects in bonsai but I can assure you that it's not rocket science and it's just a matter of paying attention. Many newcomers to the hobby make the mistake of putting a tree into a bonsai pot before it's ready. If you are putting a tree into a training pot and are not going to root prune you can slip pot just about anything most of the time. This is simply placing the root ball in another pot which may or may not be larger. Root pruning and re-potting a root bound plant will refresh it and cause it to put out fresh growth. An other important aspect of pruning is the timing, make sure that the roots are neither too dry or to wet (because the roots can start rotting). 

Once again you must know what type of tree you have. Some trees grow so fast they must be root pruned and re-potted yearly. Others may need it every other year or some exceptionally slow growers every 3-5 years. Generally, tropicals are best re-potted and root pruned during the hottest part of the year when they are actively growing. Re-pot most temperate climate woody trees just before bud break or when they first start showing fresh white root growth. Usually this is accomplished in the early spring. Some species can also be re-potted in late fall. When re-potting a finished bonsai, the general practice is to remove one half to two thirds of the old soil and prune one third to one half of the roots. The tree is then replaced in the same pot.

You should prune foliage from the tree when you remove roots. Pruning a comparable amount will save stress on the tree. For example, if you remove 1/3 of the roots, top prune 1/3 of the foliage. It may be easier to prune the foliage while the tree is still in its pot. Have everything you need at hand before you begin, tools, soil, pot, screen and wire. Do not do this in the bright sun light or the roots may dry out. Once the root are dried out, the tree will die and all efforts will be lost. Please bear in mind to chose a good spot to do the work, as this is ab absolute fundamental aspect in the process of re-potting.

Pull the plant out of the pot and attempt to untangle the roots. Some people use a root comb or even a fork will do. The roots should be trimmed all around so the tree will fit back in the container with fresh potting mix. Try to spare as many of the small, fine roots as you can. These smaller roots are more efficient at taking up water that the tree will need after the pruning.

Place a shallow layer of fresh soil in the bottom of the pot and set the root ball on it. Pour more soil around the roots, tamping it into place. Check the soil for air pockets. It can sometimes be hard to get soil to fill all crevices between the roots. One method is to manipulate a chopstick or wooden skewer between the roots to make the soil spill down. If you did not cut back the foliage yet, do so now.

Water the tree thoroughly. This will settle the tree into the new soil. The tree should be anchored in the pot some way so that the wind does not move it around in the soil. The tree should be placed in a semi-shaded location for two weeks. Do not fertilize until you see new growth. There it is, a new look and strong growing Bonsai tree for many years to come.

Deciduous Bonsai Soil Mix

The primary components are Akadama, Pumice and Black Lava. We also added a bit of Horticultural Charcoal and Haydite. These components have been found over time to provide the best drainage, water retention, nutrient retention and air circulation possible to promote healthy bonsai.

- 1/2 Japanese Hard Akadama - is a clay like component that is excellent at retaining water and it breaks down allowing roots to grown in it's place.

- 1/4 Japanese Hyuga Pumice - is a volcanic byproduct that is excellent at retaining water and nutrients.

- 1/4 USA Black Lava Rock - is also a volcanic byproduct that is excellent at retaining moisture. Black lave also adds structure to the soil.

- Horticultural Charcoal -This was added to harbor beneficial bacteria and add humic acid in the soil.

- Haydite - (expanded shale) has the ability to absorb excess water then release it slowly back to the roots.

How Do I Use It?

This is "real" bonsai soil. Be sure your bonsai pot has holes in the bottom covered by bonsai mesh.

Each micro climate may require different amounts of water. On hot days you may need to water two times while around freezing you may need to water every few weeks. Push your finger 1" into the soil and feel for moisture. If it is dry, it is time to water.

2.5 Qt = @ 12 Cups