There was no way to edit my original post, once it was published. I wish i could delete that last statement :-) Quite surprising to me that this thread did not get any interest in 2 days. I was expecting some criticism regarding the flaws in the theory.

Good thoughts, and it just seems like you're making a smaller pot. I've never been concerned about air getting in the bottom of the container. Always considered the bottom holes as just drain holes.

Yes Ed. The general thought on all the websites i came across is to discuss the bottom hole as drain hole and nothing more. Yesterday i also realized that free air flow would also improve the "breathability and hence CO2 content in the water that is in the water surface that is held in the bottom half of the container". As the air content in the water improves, that provides a fraction more in root breathing.

Yesterday i constructed a 25 gallon pot using this idea. I bought a big pot because i wanted lot of area for roots to establish. But i lost 1.4 % in height to the pumice pebbles. Ultimately, when i finished the pot with soil, i realized that i had a spare of 2" at top (after adding 2 inches of mulch cover at top). So, i could have let the bottom even go upto 0.5" which would have lost me 3% of my total height. That is negligible loss IMO. My next pot would have a bit more at bottom.

I hope Tapala comes across this thread, and makes a comment.

These are my thoughts on the subject. There are two mechanisms I can think of how air exchange takes place in the mix/media. The primary one is when a pot is water it draws air in the soil as the water quickly exist the drain. The secondary and much slower mechanism by diffusion of air molecules where the soil is exposed. Essentially in your case the bottom is somewhat exposed to air and air can enter via diffusion. The air trapped in the bottom is essentially still air and not much is going to be exchanged via diffusion. It is not going to be zero and there can be some benefit.

Thanks tropicofcancer, for the thoughts.

I am not sure if the air at bottom can be considered "trapped & still". There maybe air circulation through the bottom vents (assuming water is fully drained out), because the heat at bottom will build up inside the container, and the outside air will be relatively cool compared to inside. This will force air movement at bottom, though it maybe very slow process. In any case, this will be better than a container that has no scope for air movement at all (due to smaller particle size at bottom, with less air porosity). When we consider air movement like this, we can see why a container with 2 (or more) drain holes is better than a container with just one hole. I would be lot easier for hot air to move out, when there are 2 outlets (perhaps because wind flows in one direction mostly).

Certainly, in my case i have no worry of trapped / still air, because i am using fabric pots (which would have lot more than 2 holes). Today i filled up the second pot with about 0.9 inch of pumice (thus losing 5% of my 17 inch high fabric pot). I chose pumice because pebbles were smaller in size than (some of) the perlite that was in my mix. Vigoro perlite has particles ranging from sand size to 3/8" (maybe even some 1/2"). The pumice pebbles were uniformly around 1/4" in size.

I lost more at top of the pot (there was 2" of empty space at top) , after filling in all the soil mix i prepared. Have add a bit more mulch at top tomorrow. This idea has an added benefit of creating stability with weight at bottom, for heavy/tall plants to grow, in return for the 5% height loss.

Since hot air rises I do not see why it would easily come out of the bottom holes in the reverse direction. Hot air will expand and exit from the bottom a bit. It can rise through the soil particles and exit out the top - if there is enough free passage - sort of unlikely.

In any case, it is air in the soil that is important and so it is important to consider how air will get into the soil. I outlined two mechanisms for air getting into the soil. Soil does not have an active breathing mechanism like living creatures. Air entering soil is passive.

So I think it helps a bit to have course substance at the bottom but only marginally. Eventually they will all be clogged with finer particles from soil as water brings them assisted by gravity. I do put in some but only to prevent the drain holes from clogging too quickly. If you are using gritty mix then it is not needed either.

Giving your thread a bump. Al often catches up with posts over weekends :) May be he will notice and pipe in.

The air would have to be of very high humidity or it will dry out the roots like the "air pruning" pots. If the air is too dry it could either kill existing roots or discourage root growth in that area.

In other words you are saying that there will be more air contact inside the pot (which is good, and the basis of Al's mix). Moisture levels within the pot have to be monitored as always. Only the bottom 5% (or less) of the root area is being lost to the gravel. BTW, In coastal areas (like where i am) humidity is always above 50%.

Thank you NII13, for the critique. Yesterday upon visiting the local nursery, i saw a tree (bonsai looking, but 6 ft) growing in a 25 gallon container. Then i realized that i am way overdoing things on my first year of gardening.