Bonsai pot myth?

007

I have heard in the past that when buying or making a bonsai pot, the inside surfaces should NOT be glazed so as to allow the roots to grasp the pot. But yet yesterday, I saw a pot from a reputable potter that was glazed on the inside.

Can someone give me some more info here on this?

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hansvanmeer

Grasping roots is actually the last thing you want to happen, the easy-er the tree comes out when re potting the better it is! I think the whole glazed pot story is one of those bonsai myths.
Hans.

grampz

I personally certainly agree with this...I have probably used more 'non-bonsai' pots [bowls, dishes, trays, etc] with holes drilled for drainage in my life than actual pots made especially for use in bonsai...As a matter of fact it is only in the last 3 years that I have actually acquired a selection of 'real' bonsai pots...All of the containers that I have used in the past and drilled holes in were glazed on the inside...If you secure the tree properly in the pot, the tree roots do not need to grab the sides or bottom of the pot, and as Mr. Hans said, it makes the repotting job much easier...

I do not know for sure, but I can't help but think that the practice of not glazing the inside of a pot was more for economic reasons than for the health of the tree...Perhaps someone in the past decided there had to be a reason for unglazed interiors, so the myth was created that "it is best for the tree"...Just an opinion...

Regards
Behr

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Levon

Are you 100% sure it was glazed and it wasn't from the ashes in the kiln ? This also can look like glaze.

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jemmick

Not wanting to be different but I had never understood the reasoning for not glasing the inside of the pot to be the grip of the roots . I always understood the reasoning to be moisture retention. Dosen't this make more sense! Just mho.
Regards,
Jonathan

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Jonathan

Joanie

Moisture retention doesn't change in any high fired pot, whether there is glaze on the inside, the outside, or no glaze at all. The clay itself is not porous. The small amount of water that the clay might hold would all be in tiny chambers on the surface, and none would penetrate into the clay wall at all. So the difference between glazed and non-glazed isn't enough to hardly measure.

I also suspect that the lack of glaze on the insides of pots was economic. Glaze is costly. Glaze on the feet and bottom of the pot will stick to the kiln shelf when fired, if not removed.

It's an interesting thing to think about. Here are some other types of pots we use, and their porosity and "root gripping" texture:

1. Earthenware (low fire) like the red clay pots that you can buy cheaply anywhere. Very porous, with lots of rough inside surface for root grip. Earthenware pots are good because they do breathe (in a very small way) and CAN migrate water to the outer surface, cooling the soil inside the pot. We sweat, as humans, to cool the surface of our skin... and earthenware sweats to cool the surface of the pot. People in history used this physical property to cool water for their home use. By putting water in an earthenware vessel, it stays cooler. But it evaporates quicker. Earthenware cracks in frost because the water inside of the clay walls expand.

2. Plastic- no porosity, no root gripping, and no sweating effect. Plastic also heats up quickly in the sun, and chills quickly in the frost. No real protection for roots either way. But it's cheap.

3. Wood- wooden grow boxes would have little or no porosity, but lots of root grip. Wood also would insulate against the hot summer sun and the cool frosts, to some extent. Wood decays fairly quickly when used in a constantly damp environment. However, it's cheap and easy.

4. Stoneware- almost all bonsai pots are stoneware of some sort, or another high fire material. Stoneware can be very smooth, or very rough, depending upon the clay. However, rough or smooth doesn't really matter, because stoneware isn't porous. So it CAN have root-grip, but will not breathe or evaporate water. There is some protection from outside temperatures. Unglazed stoneware has been used for sewage pipes and bathroom fixtures.

5. Porcelain- old, high quality bonsai pots can be porcelain. You can tell they are porcelain, if they are white, and glazed. Porcelain is *usually* glazed all over, including inside, but I have not researched porcelain bonsai (or orchid or bulb) pots so they may not be. It wouldn't really matter, because porcelain is completely water proof and smooth no matter whether it is glazed or not. That's why they make porcelain toilets and sinks. Again, some protection from temperatures, but there is no physical effect as there is with earthenware.

Other views??

Joanie

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RonMartin(deceased)

Ah the great pot breathing debate. Comes up every now and again.

Do unglazed bonsai pots do it. How about glazed pots. Is it there for “breathing” or water seepage (to help cool the pot). Good questions.

A couple of years ago I was intrigued with this. I took a good quality Japanese bonsai pot and plugged up the drainage holes.

Took an ohm meter and checked the resistance between the inside of the pot and the outside of the pot. Nothing happened to the old needle.

I then filled the pot with water and did the same thing. Checked it again. Still nothing.

Maybe it just takes time for something to happen.

I let the water filled unglazed pot set undisturbed for 24 hours. Checked the pot again and the ohm meter needle shot up.

So what did this mean. What caused that needle to move.

Was it the water finally seeping through (weeping , there is a big difference) ?

If so and it is a given that water is thicker than air could air permeate the pot.?

Did my ohm meter screw up. ?

Did I screw up. (a high possibility as I am not all that smart)

Did my dog pee on the pot when I wasn’t looking ;o)

Not sure but , hopefully some of you can explain this to me. I am confused.

jeremy_norbury

Speaking of alternatives, I was just about to start a thread about these fibreglass trays I've found...

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Joanie

Ron, I'm puzzled by what you were trying to read with your ohm meter. They usually read conductivity, right? Were you trying to read the ability of the pot wall to conduct electricity, because if it did, you would conclude that there was a continuous pathway filled with water? Or enough water in the clay wall to conduct a current?

(Because clay is non-conductive usually, although what about if it has an iron oxide based colorant or glaze? I don't know.... they don't use stoneware for electrical insulation, they use porcelain. Does stoneware have conductive qualities, which are apart from its porosity?)

If you plug the holes in an unglazed stoneware bonsai pot, and fill it with water, no matter how long you let it sit, the water shouldn't seep through the clay walls to the outside. The outside should never be damp. The little chambers between the clay platelets are filled, when the clay is mature, and there is no way for water to find its way from the inside to the outside.

The way they measure porosity is by very accurate weighing, first when the clay body is (fired and) dry, and then when it's been soaking in water for hours or days. The difference between the dry weight and the wet weight is expressed in a percentage. The water that a mature (fired up to its proper cone) stoneware holds within itself is only on the outer walls, where the little open chambers are. There should be no water inside the walls of the clay.

Joanie

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