Sunday, December 7, 2008

The over watering root myth

To a thread at bonsai talk overwatering myth

I wrote this:

The subject is close to my heart since many years. Bonsai don't die of root-rot. The roots of bonsai die because of some problem, then people continue to water as before. The roots cannot take up the water because they are dead. The soil or substrate as a consequence becomes more moist than before. The tree shows signs of death. The bonsai is taken out of the container and it is clear that the roots are rotting. One can see it and one can even smell it. Also it is obvious that the soil is too wet. So the gardener comes to the conclusion that the tree was overwatered and died of root-rot.
The roots have rotted because they were dead. Trees don't die of root-rot like people don't die of FEVER. Fever is a symptom of a disease. It can be many different diseases but the symptom is the same. Root-rot is a symptom and can have many different reasons.

In general bonsai are UNDERWATERED most of the time. Our literature warns so much of overwatering that most bonsai folks underwater their darlings. Many trees suffer or even die because they are not watered enough.

Modern substrates have created a very different situation than what is described in most bonsai books. What is a modern substrate? Well, anything like akadama, pumice, crushed lave, baked loam, turface, Styrofoam flakes, coconut crush, seramins and hundreds of other materials. They all have a couple of properties in common: small particles of even size which don't decompose or decompose slowly; ability to work as water buffer - take on water and and release it alter; due to the coarseness drainage is good and aeration; OXYGEN gets to the roots easily.

Consequences if you use modern substrates:

1) You MUST water aggressively and frequently. Meaning everything must be wet whenever it is time to water. During the main vegetation period this is EVERY day. Overwatering is not an issue! It is not possible to overwater. Whatever is too much will flow out of the pot through the drainage holes. Underwatering is very well possible.ANY FOOL CAN WATER WELL! Al that one has to do is to maike eveything dripping wet. If al trees are in modern substrate ther is no such thing as individula wateing anymore!
2) Yo MUST feed aggressively and frequently. During the active vegetation period this means about every ten days to tow weeks. You should feed much more than you used to. I feed about 30 (thirty) times more than I used do in the old days when we used soil instead of substrate. You can use chemical fertilizer. The danger of chemical fertilize (namely burning roots) is not present when you water aggressively. Whatever is too much will be washed out soon. You should use organic fertilizer a couple of times during the vegetation period besides chemical. Organic is everything that smells. (BTW: it is absolutely NOT necessary to use feed cakes and to mix you own feed. Any agricultural store has everything you need for bonsai.)

As a result your trees will grow much better than they used to.
I treat all my trees including ALL my world famous trees exactly in this way. I water about 500 trees in 30 minutes. Or my wife does when I am not there. She has no clue what she is watering. And she does not need to have a clue.

Don't trust you literature! Most bonsai books were written long before we started to use modern substrates. The information in bonsai books about watering, feeding, soil is antiquated most of the time. The information is even very dangerous if you use modern substrate.


Tails said...

Very informative! Thank you! Just the kind of thing I need to read before starting my own Bonsai :)

Thanks and keep them coming! I've subscribed :)

Andrej Kek said...

Hello Walter! This thread is, as Tails said before, very informative. But I can't totally understand the fact that when using modern substrate dying of overwatering is not possible. What if there is pedestal or tray under the pot? Isn't there any chance for fatal fungus or other pests that kill roots to grow, if the substrate in pot is kept wet 24/7 and there are warm temperatures? And in your experience, is using organic and chemical fertiliser together really not harmful at all? Does fertilising with both vary from specie to specie of the tree you're feeding?

Thank you for answers and sorry for bothering, but I am really interested in this kind of "myths".


Walter Pall said...


never use a tray under your bonsai if you don't abslutely have to. Trays can be dangerous. In the subtropics and in the tropics it is always warm usuallyn moist and plants grow without too much dnanerous fungi. Don't believe what you read in old books. The substrate is never WET. This is eactly the reason for using substrate and not soil. Do NOT mix soil with your substrate. All superfluous moisture is running out of the pot and the substrate is left MOIST. Why shold it be dangerous to use chemical and organic fertilizer together? Daily practice says no. Sure there are some species which have special requirements. Azaleas for example. But I treat them ALL the same and have very good results.
Use well established modern horticultural pracices and don't trust the myths that are written in bonsai books.


Anonymous said...

thank you for this information!

Nils Arne said...

I started using substrate two years ago and have the same experience as Walter. Watering is no worries and the trees grow better. All my maples have less or no mildew on them, probably because they are stronger and healthier.
The free draining substrate also makes the trees less susceptible to overwintering/ frost damage. A huge advantage when you live in Norway.
Substrate is the way to go, now I can focus on the design and developing the trees and not bother so much with the watering and fertilisation.

TpaBayFlyFisher said...

Thank you, for telling we non-professionals the truth. For years I have grown bonsai watering and feeding as you have suggested only to hear "professionals" lecture on how the traditonal "rules" must be followed. It was almost as if they told the public a reasonable way to care for trees they would lose their "master" status. Once people of your stature dispel the often-repeated "rules" perhaps there will be more who join us in growing bonsai.

Matthieu Mavridis said...

Hello Walter,

your thread on overwatering is very inspiring, thanks ! Two questions have come to my mind by reading it. First : don't you make any difference in watering according to the species ? Second : when using solid organic fertilizer, which decompose progressively, the substrate will not drain perfectly after some months. Some fertilizer dust will remain between the substrate particles. Considering this, isn't there a risk of overwatering such a substrate ? Kind regards.

Walter Pall said...


Since overwatering is almost not possible I can afford to NOT make a difference between the species. My wife waters when I am away. She has no clue about species and their requirements. If I water, I may make some minor difference, but I don't care tooo much about this.
I am not worried about organic fertilizer eventually clogging substrate. My substrate particles are about 3 to 4 millimeters. Fine parts are flowing out with the water. What you are describing could be a problem after many years, but I am not afraid in my garden.


Nitsuj said...

well in your opnion Walter what soil is better than the modern one?

Walter Pall said...


I don't understand your question. First of all it is modern to not use any soil, but rather substrate. And then there is nothing better than modern substrate. Why is this a question??

But if you are asking whether akadama. zeolith, pumice, lava split, turface etc is better, then the anser is: IT DOES NOT MATTER! All modern substrates are fine. Akadama should not be used for old conifers and in climate zones where it gets quite cold in winter. In my climate akadama is not a good choice.


Nitsuj said...

Ohh thank you Walter, i am sorry for my english i dont live in usa anymore i live in joiville the same city you came too, I wish i had gone to nipon bonsai but i did talk to them they said that they loved having you there

Anonymous said...

Hello Walter, interesting to read this, it makes you think...
I have for exemple small "mame" growing in "modern substrats" waouh when it gets hot you've got to water the five times a day !
this summer i didn't put them in full sun because of that, as a result (or maybe for another reason i can't tell) i had no fruit on a small kaki !
Somebody told me to put the small pot in a bigger one and to cother with akadama.
Or maybe using sphagnum in the "mame" substrat?

An other question about over watering, i've got big "yamadori" pines in modern substrat. It's raining and keeps raining at the moment in Paris, would you protect them from rain?

Thank you (saw your trees in the car show in Paris, wonderful ! and your assistant is very sympathic!)

Jean-Fran├žois from Paris

Anonymous said...

Hello Walter,

Well i believe you are right, my ulmus parvifolia bonsai started loosing leaves and i was told it was because of over watering so i cut the water intake which did not chnage anything, my tree is even in a worse shape now and have no idea what to do, it is loosing more and more leaves everyday and growing less and less new leaves.

I am depserate...