Why do you say this?
FWIW, my ChatGPT says, << In the usual case, a finer medium has smaller pores, stronger capillarity, and therefore a higher perched water table . A coarse medium usually has larger pores, weaker capillarity, and a smaller perched zone. >>
This is consistent with my prior understanding and in almost exactly what I was going to write in response. The AI saved me ten minutes.
My point is that coir and peat moss are not fine but coarse. Coarse materials improve drainage and not fine ones. I think you probably know this and made a mistake with your wording. Humus is colloidal like clay, but being organic and not mineral, it has different properties, although it shares a couple as well- like holding a lot of water. The matter of capillary pull is about water moving from coarse to fine soil and not in the reverse. Gravel or small stones are coarser than potting mix, thus create a drainage problem when placed on the bottom of a pot by destroying the capillary pull.
The matter of water being pulled from coarse soil to finer soil after gravity pull stops is an essential aspect of informed gardening. For example, sometimes glaciers leave silt on top with sand directly below… you would actually be better with clay below. Knowing about this will help you strategize creating a better soil for establishing trees, in this case, at least mixing a lot of the lower sandy soil with the silt before planting (and stomping the soil down below the root ball level). It will also help you realize that when you transplant something with established roots in potting soil the surrounding soil will wick out the water when the potting soil is moister than it. Plants often die because of this before they can establish in the finer surrounding soil.
What name is “coarse bark” sold as in stores? I’ve seen pine fines but never “coarse bark.”
Running it by CHAT, my explanation of peat and coir being coarse is the usual agricultural explanation but because of their ability to hold a lot of water they are also sometimes categorized as fine, only not in the context of drainage where physical size is the main issue.
So discussion may lead to learning on both sides.
No, I didn’t make a mistake with my wording. I’m used to discussions in the Ourfigs forum regarding the potting mix for fig trees. Some of the most knowledgeable contributors also have expertise growing cannabis. Within the fig forum, the “fine” category includes compost, peat moss, coco coir, processed pine bark (“fines”), among others. The “coarse” category includes materials such as sand, gravel, crushed shells, perlite, vermiculite, diatomaceous earth, and calcined clay, among others.
I also ran it by ChatGPT. My question was simple: “Would peat moss and coco coir be considered fine or coarse?” The first sentence of Chat GPT’s response reads, “Both peat moss and coco coir are generally classified as fine-textured substrates.”
I might ask, what are they smoking, but that would be cheap. I already told you by one definition coir and peat moss are considered fine, but not in the context we are talking about. Ask CHAT if there is another definition that is usually used in the context of drainage in potting mixtures and soils. The answer should be something like this.
In soil science and horticulture literature, the same materials can be described using two different frameworks:
Structural / particle framework (what growers usually mean by coarse vs. fine)
Peat, coir, bark → coarse media because they create large pores and good drainage.
Clay, silt → fine media with small pores and slow drainage.
Water-retention framework (sometimes used in container media discussions)
When someone mixes those two frameworks in the same explanation, it produces exactly the inconsistency you noticed.
Your explanation followed the traditional drainage / capillary model used in agricultural soil science, where the key variable is pore size created by particle size, and in that model:
Peat and coir behave as coarse structural materials
Humus and clay represent the colloidal fine fraction
So the person you were responding to probably wasn’t completely wrong, but they were switching conceptual frameworks without realizing it, which made their wording misleading in a drainage discussion.
Your clarification about capillary movement from coarse to fine soils and perched water tables is exactly how this subject is normally explained in agronomy and soil physics.
If the discussion was about water retention, you would be correct.
That’s exactly what we were discussing, right? It was a discussion about the mix used in a pot. I used the term “fine” which is standard in the context of container media, as your AI states.
The dispute arose because you said that was wrong. What you should have said is that is was right in that context but, by the way, there is another context in which those materials are considered “coarse.”
The topic was about soil and its deleterious affect on potting mixes and potting medium drainage, not water retention, as I’ understood it. The primary reason soil fails as a potting mixture is because it doesn’t drain well when in this confinement because it is texturally too fine (peat and coir are considered coarse in this context), but going into it, I had never heard of peat or coir being categorized as fine, even on the subject of potting mixes, so I thought you were completely wrong until I learned this. I appreciate the clarification your comments led to and if you feel your comment was in the context of the topic that’s OK, but this isn’t really about being wrong, The facts about capillary pull and soil component textures needs to be very clear in a competent gardeners mind. The only thing that matters to me is that I help keep that straight in the minds of forum members, including my own. In this context things would be clearer if peat and coir should always be termed coarse and, really, I think it is confusing that the term fine is used to describe them in any context, but language definitions are determined by factors outside of logical control. Peat, by itself, doesn’t drain well, so it is termed fine in potting soil discussions in a kind of shorthand, even though it contradicts the usual meaning of the word- peat particles are not “fine” textured.
On the subject of fruit trees, a potting mix can include some soil when they are grown in large pots to the benefit of the trees, because large pots drain better than smaller ones.
After studying the history of the usage of the word fine being applied to peat and coir, I came to realize that this vocabulary evolved after soil science left the discussion because mineral soil, besides maybe sand, are no longer used in most potting soil mixes. The ingredients were then divided between the water holding components of the mix, which are termed fine and the purely drainage based components which are things like perlite and sand. even though peat particles are much larger than sand.
I didn’t realize this before, so, if you were only talking about modern potting mixes and not the subject of the title of the topic, you were completely correct. Comments often diverge from the original topic, and that’s usually a good thing- at least after the original question has been adequately answered. .
When a pine tree get cut down and chipped you end up with a pile that contains wood chips, bark and needles. This may be a silly question, but what is the difference, for potting mixes, between that and pine bark fines? How can wood chips be used in potting mixes, if at all?
Seems like the drainage point has been adequately addressed, but here’s a note about compaction issue in pots. Natural soil is subject to processes that keep it aerated, which might be lesser or nonexistent in pots:
I use a mix of my own for all my conifers. I use Kellogg’s raised bed mix, plus sand, plus Kellogg’s grow mulch, peat, perlite. Most conifers like it. During winter, I heel my 1, 2 and 5 gallon pots in osb frames with regular dirt. Never had a problem with drainage.
I am about to use a growing medium for both potted fruit trees and raised beds.
Basically I’m modifying a commercial tree mix which is 80 percent pine bark fines, 10 percent sandy loam and 10 percent composted mulch. My modification will be adding the extra sandy loam and expanded shale so that my final product will be about 50 percent aged pine bark fines 20 percent expanded shale and 20 percent sandy loam and ten percent composted mulch.
I’m adding the sandy loam and expanded shale based on comments about the need for anchoring in the beds as well as eliminating some of the shrinkage over time.
Any obvious flaws with this recipe?
Also regarding the perched water table, some sources have suggested a gravel layer under the beds. Would this break the capillary action and create water perching instead of the intended drainage???
My soil is pure sand interspersed with big rocks. It drains way too easily. Meanwhile, I am sure as heck not buying potting soil.
So whenever I plant things in pots, I fill up two-thirds of the pot with wood chips, put in the plant, and then pack my pure sand soil around it. Seems to work waaaaaaaay better than potting soil! 
Oh, yeah, I also tend to stick edible mushroom spawn in as well, because . . . well, I want mushrooms!
That said, I can’t keep anything alive in pots that actively grows through the summer. Our sun is just too hot, our weather too dry. So I mostly reserve pots for perennials that like very dry summers and wet winters, like daffodils. They do fine there! 
[quote=“Saw-whet, post:29, topic:79039”]
When a pine tree get cut down and chipped you end up with a pile that contains wood chips, bark and needles.
[/quote]
When you get chips from a tree removal companies that may be the case.
When you buy pine bark mulches and fines, it’s just the bark. No needles, no wood. It’s just the bark removed from the logs prior to being cut for lumber usually in the east it’s southern yellow pine. It has a big chunky bark that flakes off. Some of the othe pines, have bark that is thin and stringy that’s not suitable for mulch. Red pine.
Pine fines and mulch doesn’t breakdown as easily or cause a depletion of nitrogen like just wood chips do.