Mikecheck123
Omono
Because they get clogged.
Why Not Have Many Tiny Drainage Holes?
- Thread starter DrTolhur
- Start date
Deep Sea Diver
Imperial Masterpiece
…and then if a pot is chocked up on one side and there are holes atop and on the bottom of the slant the water table…
…as opposed to only holes in the middle of the container…
…the water table lowers more because of pressure change and a way for the water to actually leave the container?
Cheers
DSD sends
…as opposed to only holes in the middle of the container…
…the water table lowers more because of pressure change and a way for the water to actually leave the container?
Cheers
DSD sends
DrTolhur
Mame
Why would small holes get clogged if they're in the pot but not in screen? We effectively reduce the size of the drainage holes in the pot by putting a screen/mesh on top of it, so it seems like we could skip the screen step and just make the holes smaller to start with.
0soyoung, it sounds like you're suggesting the answer to the question of "why do we use one big hole instead of many small holes" is because it makes no practical difference, and (inferring here) one was selected because it's easier to make.
Mikecheck123
Omono
A screen has far smaller holes than you could accomplish with a pot. So there's no risk of clogging. And it's far thinner than a pot wall, which affect the physics of drainage.
If you're asking why don't we just make the entire bottom a screen, people already do that with pond baskets and grow boxes.
DrTolhur
Mame
I don't see why you couldn't accomplish small holes with a pot. Just poke small holes in the clay before firing. I can't comment on the physics you mention. Perhaps you're getting at things like surface tension and capillary action?
And no, I'm not asking that. I'm just asking why ceramic pots always have a small number of large holes rather than a large number of small holes for water drainage (which would allow not having to use drainage screens).
And no, I'm not asking that. I'm just asking why ceramic pots always have a small number of large holes rather than a large number of small holes for water drainage (which would allow not having to use drainage screens).
Dav4
Drop Branch Murphy
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Ceramic pots with many small holes- enough to ensure good drainage- wouldn’t survive more then a few seasons in use in my garden before the bottom became cracked because I was careless moving it. Good stoneware pots should be well built and sturdy.
ShadyStump
Imperial Masterpiece
This is a good point, taking us back to the ceramic manufacturing process.
Smaller holes means less mass between each hole to mitigate expansion and contraction due to temperature changes as well. Smaller holes could leave a pot more prone to breakage over fewer freeze cycles.
Because potters can't foresee under exactly what conditions a pot might be used by a customer, they just make them in a frost proof design by default.
Deep Sea Diver
Imperial Masterpiece
Sounds like we could use a review of @markyscott ’s wonderful resources on Introductory soil physics before moving on. Especially the discussion on water table, perched water table and particle size.
That’s what @Osoyoung was trying to explain in his message.
I confess my yearly review is overdue! try it, you’ll like it.
Cheers
DSD sends
That’s what @Osoyoung was trying to explain in his message.
I confess my yearly review is overdue! try it, you’ll like it.
Cheers
DSD sends
ShadyStump
Imperial Masterpiece
Made a world of difference to me!
leatherback
The Treedeemer
Yesterday, at my school.
rockm
Spuds Moyogi
One of the marks of a beginning bonsai potter is tiny drain holes, sometimes A LOT of them distributed all over the bottom of the pot...
Ron Lang began a long time ago using a lot of small drain holes (used to have a few of his pots with those small holes--sold them all off). He moved to larger, more strategically located drain holes as he got more experience and actually did bonsai.
Small holes don't work very well, as they tend to clog easily, don't offer nearly as effective drainage as larger holes and don't offer as much gas exchange capabilities (which is critical)
Large holes IN THE RIGHT PLACES on the bottom of the pot are hard to clog, drain better because the more water volume flowing through them, pulls water from the pot more effectively. Also they offer more capacity for aeration as their bigger volume of drainage pulls water through the soil--and O2--through the soil.
Ron Lang began a long time ago using a lot of small drain holes (used to have a few of his pots with those small holes--sold them all off). He moved to larger, more strategically located drain holes as he got more experience and actually did bonsai.
Small holes don't work very well, as they tend to clog easily, don't offer nearly as effective drainage as larger holes and don't offer as much gas exchange capabilities (which is critical)
Large holes IN THE RIGHT PLACES on the bottom of the pot are hard to clog, drain better because the more water volume flowing through them, pulls water from the pot more effectively. Also they offer more capacity for aeration as their bigger volume of drainage pulls water through the soil--and O2--through the soil.
Paradox
Marine Bonsologist
Physics
With the soil sizes we typically use, a smaller hole has a much greater chance of getting a piece of soil stuck in it than a mesh over a larger hole.
With the screen which is are smaller holes spread across the larger opening, it cant do that because of the way the soil particles aggregate/stack. They cant clog all the holes.
Lots of smaller holes in an area still does not drain as well as one larger hole because the effective surface area for drainage is still much smaller with the series of smaller holes because of the connections between the holes. It can effectively be half the drainage area.
I would bet that the pot pictured with the tiny holes in a circle wont last many years as the connections between the holes break, eventually making a bigger hole anyway.
Paradox
Marine Bonsologist
Here is a virtual of the differences between one large hole and a bunch of smaller holes that cover the same overall area
The one on the left has much less drainage capacity than the one on the right because of the area of the connections between the smaller holes.
The one on the left has much less drainage capacity than the one on the right because of the area of the connections between the smaller holes.
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ShadyStump
Imperial Masterpiece
But, ignoring clogging for a moment, if the area of empty space left by one large hole was equal to the area of many small holes, what would be the overall effect on drainage?
How would the surface tension or other hydrodynamic properties of water affect it's passing through the holes?
rockm
Spuds Moyogi
The smaller the hole, the lesser the capacity it drains...large pipe=large flow, small pipe=smaller flow.
Paradox
Marine Bonsologist
You cant ignore the clogging. It will happen and as was stated earlier the series of small holes makes that area of the pot much more fragile and at risk for cracking, which will make a larger hole anyway.
rockm
Spuds Moyogi
Another thing--drainage in a bonsai pot depends directly on the depth of the pot. Shallow pots are notorious for draining slowly or badly. That's because there is not much top pressure to drive water through. Small holes slow that process even more. A shallow pot with small drain holes is the worst "tree killer" pot made.
ShadyStump
Imperial Masterpiece
And now I seem to recall learning somewhere about this exact example. Flow rate potential through a pipe increases exponentially with the diameter. The ratio of surface area of the inside walls to the internal volume becomes small with the increase, resulting in a net decrease in friction. Capillary action and the ventury effect can add to this up to a certain point, but I'd venture a guess that these are negligible at best when it comes to holes bonsai pots.
Mikecheck123
Omono
Nice example! Might as well do the math.
If a unit is the radius of a small hole, the large hole has a radius of 7 (I used MS Paint to verify).
The relative areas are then:
small holes: 17 * pi * 1^2 = 53.38
large hole: pi * 7^2 = 153.86
The large hole has almost 3 times the drainage area!
FinnLakk
Yamadori
If you compare the drainage holes to pipes, imagine you have a single pipe and 2 smaller pipes, the smaller pipes adding up to the same area overall as the larger single pipe. The mass flow rate of water increases in correlation with the diameter of the pipe, so although you have the same overall area, more water will flow through the larger pipe in the same space of time.
In our case they are not pipes so overall flow rate is a lot more complicated to work out depending on the size and shape of the container it is planted in, however it is still safe to assume that the larger holes will flow faster.
We also have the mesh to deal with which will impede the flow again however larger holes with mesh would still be preferred over 20 smaller holes where no mesh is required. Surface tension will be a lot more restrictive on the smaller holes mainly sue to the thickness of the clay compared to the mesh screen, when travelling through the mesh it has a much shorter distance where the water molecules are separated from each other and therefore can "grab" onto each other and "pull" themselves through.
I would imagine the airflow underneath the pot helping to drain the soil would also have a more considerate effect on larger drainage holes.
EDIT: some body feel free to correct me if I am incorrect this is just what I remember from School
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