Drainage holes

[Attmos]

Are there standard drainage hole sizes for pots?
Or... maybe an average hole size for each size pot, something like that?

If not, can a hole be too large or too small?

 

[DonielDoom]

Great question. I don't believe there are standards from a crafting/manufacturing lens. From personal experience, I've found that the capillary action and/or surface tension of the water slightly impedes drainage when flowing through smaller drainage holes. I've noticed some impact to the flow of fluid draining when it nears empty. I believe what happens is: more resistance is provided by surface tension with a smaller hole (1/4" vs 1/2" for example) and therefore, more force (pressure from the water table) is required to move the fluid through the drainage hole.

This is not proven, I am not qualified to answer, and is simply casual observation from drilling out drainage holes in things like thrifted bowls/plates to use as pots. I have a 1/4" drill bit that I find drains slower than larger drainage holes. More holes of that smaller size don't seem to make an impact as the effect seems to be tied to the hole size itself.

Through typing this I'm reminded of the grade-school science experiment where we used a pipette to drop water onto a coin until the surface tension broke. Fun times!

EDIT: This is also a great time to discuss the 'perched water table' or 'water column' - I feel like there's a thread that I've found somewhere that details in a digestible manner. Hopefully I can find it.

EDIT2: This gets thrown around a bit, but I think it's touching on the same concept - https://www.bonsainut.com/threads/introductory-soil-physics.25258/post-688607

EDIT3: A thread that may be tangentially related and very worth reading as it hits a couple key bits without going into a deep dive - https://www.bonsainut.com/threads/water-column-on-super-thin-pots.63657/

 

[Wulfskaar]

To add more to this, screen size covering drainage holes seems to matter to me. I prefer screen with openings just small enough to hold the soil in, but when I buy soil or other things, they always send super fine screens. I don't use them because they seem like a lot of water wouldn't bother going through, and could get clogged very easily.

 

[Jrmcmich]

To add more to this, screen size covering drainage holes seems to matter to me. I prefer screen with openings just small enough to hold the soil in, but when I buy soil or other things, they always send super fine screens. I don't use them because they seem like a lot of water wouldn't bother going through, and could get clogged very easily.

Where do you get your drain screens from then? I feel Like most seem to be relatively small

 

[rockm]

There are no standardized drain hole size. You will find all kinds of drain hole shapes and sizes on old and new pots. In Bonsai Techniques II, John Naka devoted an entire chapter to pots and included three pages of drain hole photos if I recall

Rule of thumb is the larger the drain the better. Pots from Japan and China generally incorporate larger drains holes. Ideal for me when I look at a pot is to see holes placed evenly around where water will probably collect—center corners of rectangles, ends and center on ovals and center/evenly spaced around perimeter for rounds.

Lots of smaller holes drilled close together don’t drain nearly as well as well placed larger holes. Western potters sometimes don’t “get it” though

 

[Wires_Guy_wires]

I use drywal tape like this to cover the drain holes, it's self-adhesive so there's no need to make a flower out of wire to keep it in place: https://www.amazon.nl/-/en/Drywall-Fiberglass-Adhesive-Quality-Finishing/dp/B0CMCJ2DW9
The adhesion stops after the third watering though, but it stays in place as long as you don't poke it.
But as for drain holes go, I have plants in pots with mesh bottoms, grow bags, pond baskets and ceramics with just about any hole size there is. I can't really say it seems to make a difference as long as it's bigger than my thumb.
Mesh bottom pots with solid walls however, do seem to favor my junipers. But only them for some reason.

 

[Attmos]

Great question. I don't believe there are standards from a crafting/manufacturing lens. From personal experience, I've found that the capillary action and/or surface tension of the water slightly impedes drainage when flowing through smaller drainage holes. I've noticed some impact to the flow of fluid draining when it nears empty. I believe what happens is: more resistance is provided by surface tension with a smaller hole (1/4" vs 1/2" for example) and therefore, more force (pressure from the water table) is required to move the fluid through the drainage hole.

This is not proven, I am not qualified to answer, and is simply casual observation from drilling out drainage holes in things like thrifted bowls/plates to use as pots. I have a 1/4" drill bit that I find drains slower than larger drainage holes. More holes of that smaller size don't seem to make an impact as the effect seems to be tied to the hole size itself.

Through typing this I'm reminded of the grade-school science experiment where we used a pipette to drop water onto a coin until the surface tension broke. Fun times!

EDIT: This is also a great time to discuss the 'perched water table' or 'water column' - I feel like there's a thread that I've found somewhere that details in a digestible manner. Hopefully I can find it.

EDIT2: This gets thrown around a bit, but I think it's touching on the same concept - https://www.bonsainut.com/threads/introductory-soil-physics.25258/post-688607

EDIT3: A thread that may be tangentially related and very worth reading as it hits a couple key bits without going into a deep dive - https://www.bonsainut.com/threads/water-column-on-super-thin-pots.63657/

Thanks for those. I mentioned a hole being too large because I assume capillary action depends on the pot retaining 'some' water.

 

[Attmos]

To add more to this, screen size covering drainage holes seems to matter to me. I prefer screen with openings just small enough to hold the soil in, but when I buy soil or other things, they always send super fine screens. I don't use them because they seem like a lot of water wouldn't bother going through, and could get clogged very easily.

I've learned that drainage holes can be too small, but it kind of seems like the type of substrate used might require different mesh sizes.

Organic mixes that retain a lot of water might do better with larger mesh, whereas an inorganic mix with no small particles and lower moisture content might do better with smaller mesh size...

No idea if this represents reality at all though. lol

 

[Attmos]

Lots of smaller holes drilled close together don’t drain nearly as well as well placed larger holes. Western potters sometimes don’t “get it” though

As a matter of fact I was just reading a thread here in which the author was asking if it was reasonable to enlarge the tiny holes in a pot by a well known maker. It looked like the general concensus was not to modify the pot because of the maker, but the author seemed to think they weren't draining well.

 

[Attmos]

This is not proven, I am not qualified to answer, and is simply casual observation from drilling out drainage holes in things like thrifted bowls/plates to use as pots. I have a 1/4" drill bit that I find drains slower than larger drainage holes. More holes of that smaller size don't seem to make an impact as the effect seems to be tied to the hole size itself.

That's actually what I'm doing. I've collected several pieces of pottery that I'm putting holes in. Most are hand made so I don't know how well they'll deal with temperature change, water, expasion.. etc... but it's a fun way to spend time.

I can do any size hole, any number of holes, in any part of the pot.. so I'm just looking for guidelines if there are any.

Another curiosity is if aesthetics matter, as far as the bottom of a pot goes...

 

[Wulfskaar]

I use drywal tape like this to cover the drain holes, it's self-adhesive so there's no need to make a flower out of wire to keep it in place: https://www.amazon.nl/-/en/Drywall-Fiberglass-Adhesive-Quality-Finishing/dp/B0CMCJ2DW9
The adhesion stops after the third watering though, but it stays in place as long as you don't poke it.
But as for drain holes go, I have plants in pots with mesh bottoms, grow bags, pond baskets and ceramics with just about any hole size there is. I can't really say it seems to make a difference as long as it's bigger than my thumb.
Mesh bottom pots with solid walls however, do seem to favor my junipers. But only them for some reason.

I saw @leatherback using that tape in one of his videos as well. I may have to try it out.

 

[Wulfskaar]

Where do you get your drain screens from then? I feel Like most seem to be relatively small

The ones I was using were similar to *these* in size, but square and cut out of a larger sheet. I can no longer find them.

I was going to go to the hardware store before repotting season starts to see if I could find a big sheet of it. I may just get some drywall tape instead.

 

[Paradox]

Where do you get your drain screens from then? I feel Like most seem to be relatively small

This is what I use cut down to whatever size I need to make sure the hole is covered.
The link is for 7 count mesh. You can also buy 10 count mesh for smaller soil particles used for small shohin and mame if you need that

https://www.amazon.com/Caydo-Crafti...-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1