Friday, June 19, 2009

root rot

I got this mail:

>>> Mr Pall,
> I recently read your blog post on root rot and over watering. I would like for you to clarify something. Did you mean it is impossible to over water a well draining soil mixture?
> Then, what causes root rot?

Root rot can be two things. A rare fungus can infect the roots and kill them at least partially. They die and rot. This is a rare thing and has NOTHING to do with over watering. The fungus kills anyway, whether over watered or not, but it can be much more aggressive when the roots are all wet. Bonsai practitioners should NOT worry about this. It is very rare.

So what is the famous root rot that trees die off when over watered? Well, trees (apart from the 'real' root rot) don't die of root rot! And root rot is not necessarily a consequence of over watering with bad soil. It can also be under watering or many other things. It is simply this: For some reason roots die and then in a moist environment they will rot. When the bonsai enthusiast then finds that something is very wrong with the tree and takes it out of the pot he finds rotted roots. and He 'knows' that this caused the death. The truth is that rotted rots are a symptom, like fever. In the old days the would say of early settlers 'and they died of fever'. well, this was simply an acknowledgment that they had no clue what they had really, but they had fever anyway.
bottom line: TREES DO NOT DIE OF ROOT ROT! Trees die and then the roots rot. The gardener has to find out what was the cause of death when he sees the symptoms. you have to find the cause of fever.

When do trees die from over watering? When one uses an old-fashioned bad soil then there is not enough drainage. Water cannot flow off easily. Water will stay in the root ball and not keep it moist but wet. As a consequence the entry of new air with oxygen is blocked and roots suffocate. Roots must have oxygen in the air otherwise they will suffocate and die. Thus over watering in combination with bad soil can well kill trees and when they are dead they show root rot as symptom. Under watering can kill roots by simply drying out. When you then later on water again the dead roots will rot. it is the same symptom, but a radically different cause.

Modern substrates are very well draining and aerating. It would be difficult to over water. One can pour water into a bonsai with modern substrate for several minutes and all the superfluous water will flow out of the drainage holes and there will be free access of new air and thus roots will get oxygen to breath. If you insist you can over water still, of course. Just pour water in for hours. But who would do that?

Root rot is a bonsai myth.


Andrew said...

Thanks for clarifying that for me Mr. Pall
Andrew R

Anonymous said...

I think you should make a post called "Myth Busters" !!
You are at your MOST entertaining when you are busy "Busting" Bonsai myths;-)

Yet again you teach us in a very straight forward, clear AND funny way.

Thank you.


Stavros said...

Dear Walter,

Your explanation is very logic.
Hydroponics are based on good aeration and high levels of moisture on the plant roots, in a very well drained environment and when done properly, there are no problems with root rot. Not only there is no root rot, the plants grow at their maximum possible pace.

Anonymous said...


I don't quite agree. Yes, root rot is a fungus born disease. But this is an anaerobic fungus whose proliferation is directly stimulated by lack of oxygen, itself often the result of stagging water in the pot ( oxygen is not very soluble in water) so consumption of oxygen by the roots results in good conditions for root rot. This is not a myth.

By the way, though I don't doubt that you don't have any root rot problem with your trees (rather big trees and big pots) I can garantee you that I did have root rot on small pines in very fast draining substrate that regressed without treatement just by watering less.
I think that there is a problem of scale which makes root rot less susceptible to happen in high pots, in which the situation is more like in soil.


Walter Pall said...

It seems that you have not really understood what modern substrate does. It allows oxygen to get to roots even if you water like hell. There will always be enough space between particles for air to get through. Thus over watering is almost impossible, If the roots consume oxygen and then as a consequence fungous attacks them then this is a clear sign that one used the wrong soil, like we all did twenty years ago.
It sounds to me like you are using old.fashioned soil.


Anonymous said...

As I wrote, I use a very fast draining substrate : 90-95% lava rock 6-10 mm, 5-10 % white peat.

I have this problem only for young trees in small pots. With the same mix in big (high) pots and bigger trees, I don't encounter this problem.

Walter Pall said...

You don't seem to know that I have one of the largest collections of shohin. I have around 200 inn very small pots. No problems with root rot. All trees are heavily watered every day.


Anonymous said...

Please, don't get me wrong. I am a big fan both of your artistical work and of the way you cultivate your trees. Over the years, I have come to use all of your recommendations (white peat as the organic part of the substrate, heavy fertilization just after repotting and the like) with great satisfaction.
Yet, the watering part fails for some of my trees...
Best regards,

Broken.Arrow.Bonsai said...

Just confirming Walter's substrate/watering comments for others. I use haydite/lava/pumice in some combination (equal, or just one aggregate). I have only 1 tree w/+25% organics, only because it was purchased this way. It has been 100+ the last few days in Tulsa and ALL of my trees are doing very well. I water a couple of times per day but I believe the substrate actually helps the tree be more drought tolerant by only holding a small amount of moisture where the tree can draw from that continuously. I do use sphagnum on my pots to prevent evaporation. I am getting the fertilizer routine worked out. I developed a bit of chlorosis which is quickly fading now that I am feeding more heavily. Digging into the post, I can clearly see it filling up quickly with numerous small feeder roots. Trees have never looked better!!

Katvet00 said...

Dear Mr. Pall,
I am a first time bonsai owner, and I am doing some reserach on how to take care of it. I found that my double white snow rose has 6 yellow leaves on it, and it's getting worse. I went to another website and it said that it could be a symptom to root rot. I water my plant every day, about 1/2 of a top of a bottle. (label and up) I give it fertilizer every other day after I water, about 300 mg. I don't know if thats the problem. Well anyway, I decided to see if it had root rot. The soil held together good, thank goodness. I found that my bonsai had Brown roots with slightly black patches on them! I don't know if it's the natrual color of the roots, It is a double white snow rose and it's quite young. I got it out of state, from VA/MD to GA/AL(is that right for alabama?(not allowed to give location out on internet) My soil is to be damp all the time, but the top keeps drying out! I have it on a plate to drain properly, and the drain holes aren't touching it. I really am confussed. Do I have root rot or what!? Please help, and you can call me Katvet00( not allowed to give real name on internet)Thank you!

Walter Pall said...

the roots msut have white tips, can be dark or black otherwise. If they don't have white tips you have a problem. It may well ber that your plant is in poor soil which acutally makes roots suffocate. They die and later rot. So the cause is not root rot, it is the symptom. The other symptom is that the tree looks like it needs water while you are wateing all the time. A sure sign for severe root problems. You will have to change the soil to modern substrate as soon as posible. Now is about the worst posibel time to repot though.
I would piut the tree into shade all day and water little but moist the foliage severy times a day.

katvet00 said...

Well, I looked at my tree again and found that those were just part of the root sticking out. The rest of the roots that had tips sticking out were white. Also, the tree was growing perfectly fine when I bought it a few days ago. So I really don't think soil change is nesssisary.(did I spell that right?) There are more details in the letter I'm sending. This will be sooooo cool! I've never mailed international before!

nick G said...

A thought or two about root rot...

Bonsai is the art of miniaturization, we as a (members of a long line of artists) have inhertited the knowledge to see and understand what is reflected in nature. Almost every rule of Bonsai mimics the rules of nature. The Art teaches us to layer the soil with the finest soil on top just as nature would do. The Art has taught us to wire branches to simulate the downward pull upon a branch by age and snow. We even simulate how the earth takes its nutrients from animals and fish. Even to the layman, these roots of the Art cannot be denied.

Yet, this said, some of us deny that the roots of a miniature tree cannot fall victim to its normal size bother.

Could it be that this most common of diseases breaks the rules of Bonsai?