I agree with everything Tiffany said.
>> Whatever kind of soil or mix one has , NOT packing it tightly into the pot can help preserve tiny air spaces.
I agree you can't just "tamp it down" tightly, the way you might stomp on the soil around a tree or bush that you just planted outdoors in dense soil. especially in a pot.
But when I try to "add air" to the soil in one of my outdoor raised beds, I do a little "firming" of the soil after amending with chunky stuff and compost and then "fluffing it up".
Here's my theory: after I fluff it up with a garden fork, the soil is very loose and maybe as much as 30% air in large pores. But it's unstable. Just the weight of soil and mulch would soon compact it down too much, and rain or watering would make it slump and run together horribly like thick soup or thin pudding. The clay would "dissolve" and run down to fill ALL air gaps. The clods that were barely supporting each other would collapse and lose their structure.
My theory is that I need to firm it down "a little" so that clods touch semi-firmly without air spaces collapsing, and big chunks have a chance to sit upon each other and "lock" into place. It seems to me that once it has been "firmed" a little, the remaining large air spaces (15%??) are more stable and the clay seems more inclined to "stay in place" inside clods or peds, instead of turning into soup.
If true, it's another of those darn gardening "Goldilocks principles", like in the story "The Three Bears".
The porridge had to be not too hot and not too cold. It had to be "just right".
But what the heck does "just right" mean? If you don't already know what "just right" feels like and looks like, and how to create and maintain it, what good does it do to know that something needs to be "just right"?
In gardening, it seems as if everything is the "Goldilocks principle".
Seed-starting mix has to drain well enough to stay aerobic, but can't drain so fast that the seeds dry out between waterings. Potting mix (and garden soil) also need to hit that "golden middle", balancing drainage and aeration against water retention.
Soil has to be "fertile enough" for the current crop, but no mineral may be concentrated enough to hurt root hairs. Total soluble minerals can't be excessive or the plant will die of salinity. Over-fertilization kills plants, and under-fertilization slows their growth.
You can't overwater, or roots drown. You can't under-water, or plants will sulk and wilt.
Each plant needs the right amount of sun. Even plants that need "full sun" may not be able to take "full sun" in a Texas or Arizona summer afternoon.
Temperatures have to be warm enough but not too hot.
Day length has to be long enough, but nights also have to be long enough. Sometimes you even need daylength to be in creasing or decreasing - by just enough.
And experienced gardeners give advice as if we "just know" what is "just right", like Goldilocks apparently does.
I think that gardeners who learned by watching an experienced gardener are incredibly lucky. They were able to see and feel what was too compacted, over-watered, over-fertilized or burned by the sun.
Those things are hard to put into words. The closest I've seen is explanations that stick to "operational" definitions.
"The soil is too heavy IF you squeeze a damp handful of soil firmly and it clumps into a hard ball.
It's too loose if it falls apart when you open your hand.
It's just right if you have to poke it a little firmly before it crumbles.
it doesn't drain well enough if water runs off the surface during a rain.
It drains too fast if plants wilt one day after a good rain.
It's too hard if you try to push a shovel into the ground and the shovel blade bends."
"Operational" definitions say to do X, then look for Y or Z.
That tries to avoid the need for you to be Goldilocks ... except that it does require you to "just know" what is meant by "damp", "firmly" and "hard".
I think most of us who did not learn at our mother's knee have to learn by killing plants and guessing at the reasons.
"They all died ... maybe they were over-watered!"
"Hmm, they all died again, maybe this time it was over-fertilization."
"Hmmm, they lived until they turned into 6-inch-tall spindly stems and then all fell over dead. Maybe not enough light?"
