The Art of Watering

Introduction

Of all the frantic phone calls and urgent emails I receive from people worried about their bonsai, I'd say 90% of them are experiencing problems which relate to watering.

I have cringed at every terrible piece of advice given by well meaning but nonetheless ill informed garden center employees and sales assistants; from watering once a week with 250ml of water to misting several times daily.

Watering is an area of our art which I think is assumed you will intuitively grasp, after all it simply involves getting water into a container with a live plant in it! In reality though it is actually a rather complex technique which just like wiring and styling needs to be practiced and mastered. I have heard it said that it can easily take a full time apprentice 3 years to grasp the essentials, so how much longer will it take you and I as amateur enthusiasts? This is why I have entitled this post the ART of watering.

Image caption. Watering is a technique which needs to be learnt just as wiring and styling.

No doubt you will find many articles pertaining to watering of bonsai on the internet and this one will simply add to those already published. However if after reading this article you pay more attention to your watering habits and their results on your bonsai, then I would have achieved something.

Why does a plant need water and how does it use it?

Please don't close your browser! I promise, this is not going to be a biology lesson but it does help if you understand how a plant fundamentally works.

Basic plant biology

Depending on the type of root system, the species of plant and the size; the plant will have a certain number of root hair cells. These cells normally coat the outer layers of branches and will appear shiny and similar to silk. The process of osmosis is accelerated by these cells and they act in a manner which is similar to photosynthesis. However rather than absorbing sunlight, they absorb water which they transport through the plant or tree for a variety of purposes.

Image caption. Just behind the white actively extending section of these roots of an elm, you will see very fine root hairs.

Very importantly some of this water is used in the process of photosynthesis. Some of it is used in vegetative growth and some help to cool leaves. If the surrounding air is warm and dry, more water is used for this purpose.

Tip! Therefore if you are keeping trees indoors and you use an air-conditioner the air will be dried and thus you will need to pay attention to how quickly the growing medium dries out.

Plant nutrients are also absorbed in the same manner of osmosis, in fact these processes of absorbing water and nutrients happen at the same time. Just like water, the plant may save these nutrients for later use or may utilize them immediately.

Telltale signs of incorrect watering

So how do you know if you are not watering correctly?

In many public demonstrations I have been asked by someone who had purchased a juniper from a retailer and after caring for it for a few weeks noticed gradual and eventual full die-back of the tree, the needles first lightening in colour and then eventually going brown. Generally my response, after further probing questions, is that the tree most likely was 'killed' whilst it was still on the shelf, before they ever had it, it's demise most likely due to insufficient water. The trouble is that with conifers particularly, shocks such as prolonged dryness only manifests a few weeks later, leaving the owner believing they did something wrong and thinking they cannot care for bonsai.

Other species such as Celtis will drop their leaves rather quickly in periods of drought in an effort to survive. If they then receive water again before the tree has been dry too long they will recover and new leaves will emerge.

These are both examples of insufficient water but what happens when trees get too much water?

Roots begin to rot when they are kept wet too long, this is as they need oxygen and if the available space between the particles of your growing medium is taken by water there is no space left for oxygen and the roots will drown. This is again not something which happens immediately. The conditions in the medium though are ideal for a fungus, Phytophora. This fungus is naturally found in soil but when conditions are right they will attack the roots of trees.

Image caption. Note the rotted roots and the very wet, organic soil they were growing in.

Tip! Its important to note that if you are using a 'modern' growing media such as something made up of akadama, pumice, leca, groperl etc then it is pretty much impossible to over water. Over-watering generally only occurs if you are using a lot of organic material such as milled bark, compost, garden soil etc.

In summary here are a few of the signs to look out for, although this is not definitive and sometimes it is not that easy to identify the cause of a problem without sufficient evidence or further investigation:

Too little water

• Yellowing and wilting leaves or even dried leaves near the bottom of the tree. In advanced cases branches will have died.
• Depending on your growing medium, some materials such as some peat, milled bark and other similar organic materials are extremely difficult to wet should they dry beyond a point - they become hydrophobic. At this point water which is given to the tree simply runs over or around the soil mass and the trees roots do not actually receive any at all or not enough.

Image caption. Japanese maples, especially the lace leafed varieties are very susceptible to damage caused by insufficient water, especially if the wind is blowing and increasing water loss.

Too much water

• Dull needles and scale foliage in conifers especially.
• Smaller, yellow or sparser than normal foliage.
• Leaves are wilted but the growing media is moist.
• Trees with a thin bark which is normally smooth will appear wrinkled.
• Die back of branches for no reason you can think of.
• When re-potting you find dead or dying roots.
• Bark covering the roots is soft and the inside decaying.
• Roots are fragile, break easily and are "mushy."
• On the surface of your growing medium liverworts flourish. 

Factors which influence watering

As I wrote earlier, watering is not as easy as some would lead you to believe. When someone asks me how often and how much to water their trees I always hesitate when answering. The reason is that without sufficient facts, I am unable to give a reliable answer.

What facts am I referring to:

1. What species is the tree? Some trees like more water than others. For instance a Swamp Cypress can be grown with its roots partially submerged in a bowl of water but doing the same to a pine will kill it. Know what species you are growing and water for their needs, do not practice blanket, blind or routine watering.
2. When last was the tree re-potted?  As the tree is unable to take up much water now that most of or at least a large portion of the roots hairs it uses to do so have been removed you need to water less (and keep the tree in a sheltered spot). You will see that just after repotting a tree, the growing medium remains moist far longer than usual. It makes sense then that until the tree has been able to re-establish itself watering should be reduced.
3. Is the tree actively growing? It is only when a tree is growing that it requires frequent water. During periods of low (height of summer) or no growth (winter dormancy) less water is required by the tree, as explained in a paragraph on the basic biology of plant roots.
4. What does your growing medium consist of? If organic material makes up a large proportion of your growing medium (such as our General Soil Mix) then you will need to water far less than say someone who has their trees planted in pure LECA or our Professional Mix for instance.The reason for this is that organic material will hold or retain a lot of water keeping the medium wet much longer, whereas something like pumice, which is a superb growing medium, will absorb water but release it much quicker.
5. What is the placement of the tree? If you have a bonsai tree on a cement balcony which receives afternoon sun and regular wind your tree will need far more water than someone who has their tree under shade netting in a sheltered spot in their garden bordered with hedges. Trees lose water through their leaves to remain cool; reflective, dry and hot surfaces such as white painted walls of a courtyard, black slate tiles which are often used to display trees and other such artificial materials reduce levels of ambient humidity and elevate local temperatures increasing moisture loss of the tree. On the other hand a cool micro-climate created by shade netting, organic mulches around the floors near to your benches and living hedges will provide a far less extreme situation for the tree and they will likely need less water. For indoor bonsai; is the tree placed on the window sill in the heat of the day? Is it in an air conditioned environment where it is cool but dry? Consider these factors and assess the water needs of your tree accordingly.
6. What stage of development is the tree at? If the tree in question is young, growing strongly and being developed for styling then it is most likely that more water will be needed, especially as you are most likely feeding it grossly. However if you are regulating needle length in Japanese white pines, then withholding water is one method which can be employed.
7. Has the tree been defoliated recently? A tree without leaves will use far less water than one which has a dense canopy of leaves. Adjust your watering for these trees accordingly and do not simply continue with the same routine you had before.

Image caption. When you repot a tree a lot of the roots which were used by the tree to take up water will now be missing. It stands to reason then that the tree should receive less water until it has settled and issued new root hairs once again.

Tip! If you want a tree's growth to slow down, for instance when it is nearing 'completion' and ramification is dense, then you keep the growing medium wetter as root hair development is reduced. When you want to speed up the growth of the tree you can water less, within reason of course, combined with a very open or fast draining growing medium, root hairs will be provided with plenty of oxygen and will develop rapidly in an effort to seek out water.

When to water

Time of day

I was brought up believing that one should never water during the heat of the day, that you should only water in the early morning or evening. Failure to heed that advice would lead to leaves which have been burnt by the water droplets on the leaves acting as magnifying glasses for the sun's rays. In my experience this information is not true as I generally water during the day between 11am and 1pm and do not have any burnt leaves on any of my trees.

The reason I water then is that the day is broken roughly in half. If I were to water once per day and only in the morning, then the tree would need to go the whole day without receiving water again, and as I use a modern growing medium the tree would not make it. If I were to water every night I may create conditions conducive for fungus and snails and slugs. Watering around midday allows any water which may have landed on the foliage to dry completely by evening.

Of course you will need to find a time which suits you and your lifestyle. I am fortunate in that I can largely determine my daily program and can ensure I am around to water then. If I think I may not be able to make that time slot then I would water either before or after, but preferably in the morning rather than evening.

Due to the drought in the Cape at the moment I have moved over to watering in the early evening. The thinking behind this is that the medium will be able to remain moist for longer and allow the roots to absorb more water over an extended period of time. Some trees have been mulched with spaghnum moss and some have been "double potted," ie the potted bonsai placed on top of another much larger container filled with growing media.

Dryness of the medium

Once again, considering the questions asked earlier (1 through 7) you will generally need to water when the top 10mm or so of the growing medium is fairly dry to the touch. If you are using a very organic mix then if you rub some of the medium between your fingers or even insert your finger slightly into the medium it should not come out looking like mud. 

Tip! One of the nice things about using akadamain your mix is that when it is wet it goes a dark brown colour and when dry it is light brown. So it is easy to see when you need to water again with the colour changing effect.

Image caption. When Akadama is dry it has a light brown or tan colour to it so it is easy to see when it requires more watering.

You never want any medium to become bone dry.

How to provide water

I am not an expert on irrigation systems so I can only tell you what I do know. To my knowledge there are two broad approaches:

1. Hand watering
2. Automated watering systems or commonly known as irrigation

Hand watering

Immersion

If you only have a couple trees then perhaps immersion is the best method for you which is also very water-wise, a topic which has become very relevant in our drought stricken country. All you need is a container which can hold water.

1. Take the entire tree and dip it into the container so that the water drenches the entire pot.
2. If the growing medium was particularly dry you could leave the container immersed in the water for a couple minutes.
3. What you should notice is that a lot of air bubbles will rise to the surface of the water. This is old air which when you lift the container out of the water will be replaced by fresh air. This is great for the roots.
4. If you place a grid over the container then you can place the bonsai on the grid and any excess water can drip back into the container. You can continue using this water and simply top it up as needed every couple days. Or the container can be emptied occasionally and the water replaced.

Tip! This method is also great if you are using a liquid fertilizer for your trees such as Hortisol, as you can mix it with the water in this reservoir and in this water fertilize all your trees when watering them also.

As I mentioned, if you only have a few trees then this is a very attractive option, you can even use the kitchen sink! Problem is that should you have a lot of trees or the trees you do have are large then this is going to be a back breaking method to use for watering them on a daily or frequent basis.

Hand watering

Image caption. Now available from Bonsai Tree these plastic watering cans are comfortable to use, easy to carry and have a fine spray.

Watering cans are available in many shapes and sizes as well as in a variety of materials. You can use a small plastic watering can which will probably cost you very little, or you can use the real deal copper watering cans from Japan. The latter is claimed to posses antimicrobial abilities but these cans are costly (upwards of R3500) and probably present an irresistible temptation to thieves should it be left outdoors in South Africa. Whichever watering can you choose it should be comfortable to use when transporting the water and when pouring. It should also have a fine spray which will not erode the growing media from your bonsai pots, and it should not leak all over the place.

Fine sprayers or spray-wands can also be attached to a hose and watering is made that much easier than having to cart cans full of water all over the place. However should you only have a small collection a watering can will be good enough, but larger collections will demand a watering wand or similar attachment. Once again you should look for one which has a fine spray, and do not open the tap to full blast, preferably use it at low pressures.

My method of choice is hand watering with a wand. The method forces me to make daily contact with my trees, unlike an automated system, so I can pick up any problems with drainage or pests quickly. I can also easily adapt my watering to suit the needs of the tree, for instance if I have just defoliated it then I will water it less. All these considerations are borne in mind as I am walking through and watering, and I respond accordingly. This is a lot easier than to have to adjust spray jets and dripper nozzles.

Image caption. When you water make sure you do a thorough job of it and get the watering running out the bottom of the container.

When you do need to water a tree which is growing strongly and is not infected by any pest you do not simply spray it with water and move on, or pour 250ml of water onto it or mist it! You need to water at least twice, so that water runs from the drainage holes - move onto the next tree and then repeat this with the first again. Sometimes deeper containers or compacted root balls, particularly those growing in old akadama may need several more passes before it is safe to say that it is watered properly. 

Tip! A watering can is useful even if you predominantly use a hose with a spray-wand on the end as it will allow you to spot water those trees which either you avoid when watering with a hose or those which require a little watering top-up during the day.

Automated Systems

Drippers or drip irrigation

This method seems to hold a lot of promise for bonsai growers and it is very water wise. There are many bonsai artists of international acclaim who use this method. My understanding though is that they generally use this method only when they are travelling and not on a daily basis when they are home. Although in principle I guess that there is no problem with using it as your main method of watering, I would be nervous of relaxing and not checking on the dripper lines frequently because I am pretty sure they can quite easily become blocked.

Drip irrigation is defined on Wikipedia as follows: "Drip irrigation is a form of irrigation that saves water and fertilizer by allowing water to drip slowly to the roots of many different plants, either onto the soil surface or directly onto the root zone, through a network of valves, pipes, tubing, and emitters."

Image caption. Drip irrigation holds much promise for bonsai enthusiasts and is a very water wise method of watering your trees.

Unfortunately I know little of this method and I do not know anyone in my general vicinity which uses it, thus I am not able to comment. If you are reading this blog and do use this method perhaps you would care to comment and share with other readers your experience and observations.

Sprayer type irrigation

In my opinion and experience this is probably the last method I would consider using to water my trees, certainly on a regular basis. The reasons I dislike this method are:

1. The wind which frequently blows in Cape Town makes it very difficult to wet a tree properly and a lot of water is wasted.
2. Trees with a dense canopy are very difficult to water in this manner as the canopy works like an umbrella and water mostly runs off the tree and not into the container.
3. It is very difficult to position the sprayers so that watering happens evenly on my benches as one tree obscures another and so forth. Wind, as mentioned above compounds the problem.
4. I lose touch with my trees. The realities of modern life, and being father to a 2 year old, are demanding on my time. Inevitably when you utilize a time saving method like this, you end up using that time elsewhere and before you know it you only get to check on your trees occasionally. By then one of them has been subjected to dry conditions too long and the damage has already been done, or perhaps you miss the start of a mealy bug infestation and have to do damage control.
5. Reliability of these systems is somewhat questionable. I know of at least a few people who have lost trees and even entire collections due to the failure of the system to turn on because the electricity tripped or the battery in the timer was dead or some other basic problem.
6. Blockages. The little plastic nozzle which determines the spray direction and dispersion can sometimes pop out, leaving you with a small water fountain. The nozzle, especially the low flow ones can easily become blocked.

Image caption. Irrigation with sprayers is a very attractive method especially if you travel a fair amount. 

Seems to me that these systems are often more trouble than what they are worth, however if you differ with me that's perfectly fine. I guess if I were not able to make a plan for someone to water my trees when I travel then I would also have to consider using a system of this nature.

Water Sources

For most of us we get our water from a municipal source. However there are other sources and depending on the quality of the source you may or may not observe certain results on your trees.

The main types of water to choose from may include the following:

Rainwater

This form of water is arguably the best to use on bonsai. If you have some space for the necessary tanks, this water is free to collect and your utilities bill will come down as not only are you using less municipal water but you are also putting less water into the effluent system and thus will save on sewerage processing charges.

Image caption. There are rainwater harvesting tanks of many different shapes, sizes and colours to suit your home environment. Get one! The sooner you do, the sooner you start saving on your utilities bill.

It is truly amazing how much water can be collected from the average domestic homes roof and if used carefully it can actually last for several months (depending on storage capacity, how large your collection is and how it is used)

Personal note. I have 7500 L rainwater catchment capacity next to my house in a spot which was previously unused. I have a small irrigation pump connected to it and I use this connected to a hose and watering wand to water my trees. As I walk around I am constantly kinking the hose when I am moving to the next tree so no water is wasted. Furthermore I have a 'bypass' on the hose and the water which does not go through to be used on the trees goes back into the tanks, injected vigorously which serves to aerate it also. This places less strain on the pump motor, by reducing the workload (Explanation: Centrifugal water pumps, not the submersibles, are cooled by water passing through the impeller housing, so it is important that there is always water movement. Higher back pressures from a restriction such as a spray wand or other attachment causes the pump to work harder increasing the electricity it uses and increases wear on the seals).

Distilled water

Water which is boiled, allowed to condense and is then captured is distilled water. You can buy this water from pharmacies and other such places. It is going to be prohibitively expensive in my opinion if you have a few trees, and if they are anything larger than a mame! 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.

Purified water (Mechanically filtered)

This is water which has been passed through a membrane or cartridge type filter of some sorts to remove odour, sediment, salts, bacteria and more. There are various degrees of filtration starting with the commonly used domestic under counter type filters to the more sophisticated RO systems (Reverse Osmosis). This method of water treatment could be used on rainwater (although I don't think it is necessary), borehole or other surface water sources, or even poor quality municipal water. It would be best to research your water, preferably having it analyzed in a lab, which is not that expensive by the way, and then determining which filtration system you need for the water to comply to irrigation standards. Water treatment to achieve irrigation standard water is nowhere near as stringent as those for potable water but it would still be best to consult a water treatment company for a solution.

A system which seems to be somewhat popular in areas with particularly bad potable water is RO. These systems have become a lot more affordable as the technology has been developed over the years. However be aware that although RO is used on an industrial scale in desalination plants, domestic RO systems are not designed to remove salt from brackish water. It may work for a while but it will eventually fail, so in those conditions you will need a small industrial unit. Unless RO is your only option I would advise staying away from it as it does strip the water of everything and it is also a rather wasteful process as a lot of water is used to backwash the filters. There are cartridges which claim to have remineralizing properties but as I know little about these I cannot comment on their effect on the growth of plants.

Image caption. The components of a typical RO or Reverse Osmosis system.

If you have access to a borehole you may experience high levels of metals. This is generally not a problem other than an aesthetic one. The bark and leaves of your trees will be discolored but your tree will not actually suffer internally as it will only absorb as much of the metal as it needs, discarding the rest. However I am not sure what the long term effect on your growing medium might be and its ability to absorb other nutrients. A relatively simple fix is to aerate the water (with a venturi or even an air-stone powered by a small or even aquarist oil free compressor), which will oxidize the metals causing them to precipitate. They will settle to the bottom of the tank, and you can simply drain the tank every couple years and clean the sludge out. There is filter media such as MADDOX which you can use in a sand filter for an inline solution, which will also help to reduce metals but once again, consult a water professional on this.

Tap water

The quality of tap water varies geographically, and supply sometimes can be hampered by burst municipal pipes or for other reasons. Its probably the most commonly used water type among bonsai growers as it is generally so accessible. I think for most people this water will be fine for use. Should you suspect the water to be very high in chlorine, fill a large vessel with it. Allow to stand for some time, perhaps overnight and then use a watering can to apply to your trees. You can speed up the process by bubbling air through it. Or you could use a very simple two stage filter, with the first filter removing any particles (such as sand) and the second containing activated granular carbon. This filter will remove the chlorine and/or other chemicals from the water.  

Image caption. A simple GAC filter element can be used to remove chlorine from water.

The effect of salts

High levels of salt can result in a sort of burnt or yellowish look to the leaves of your trees and especially high levels will manifest as white crystalline deposits on your pots. Low levels of salt is preferable for most species and will promote healthy growth in the tree. Indeed in some species which are intolerant to salt such as some junipers, using water with high salt content can have a very bad effect.

Conclusion

I think this must be the longest, single blog post I have ever written. The fact is though that I have just scratched the surface and introduced you to some of the theory, much of which I am sure you were already aware of or familiar with. However if you have learnt something then I am very glad, and if you will now pay more attention to your bonsai tree's requirements for water and not simply water as a matter of routine then my objective has been achieved.

I would love your feedback and perhaps you have some comments to add. Please feel free to do so in the space below, and thanks so much for reading.