What makes a smart pot smart?

Let’s imagine your plant is in soil, it’s roots spreading out and one root tip finds a stone. It changes direction to grow around it and then continues to fan out from the main stem.

In a conventional plastic pot, the root reaches the plastic wall, and tries to grow “around it.” In the process it can grow in a circle, the beginning of a hangman’s noose. As it wraps around the pot, few other roots grow, because those root tips are producing auxins preventing other roots from forming.
A smart pot, be it fabric or plastic does something different; it allows the perimeter/outer layer of soil in the pot to dry out more quickly than the core. When a root reaches the pot wall, the root tip ‘dies’ because of lack of water and exposure to air. The production of that hormone/auxin is stopped and new roots form, much like nipping out a growing bud, to encourage bushy growth. A hairy healthy root ball is formed, rather than a strangulated snake-like root ball. It also prevents the pots from becoming root bound.

The four big air pots I’ve used, do what it says on the tin, lovely roots, good crops but the pots are pricey. I bought them as an experiment.

It’s cheap to use spun weed suppressant material (not the plastic woven material similar to an ikea blue bag) My how-to video is on Youtube. all you need to remember is that PI x diameter is the length of the circumference, volume is PI x radius squared, x height of the pot and you’re off. Most modern thread is nylon so is probably going to outlast the fabric. I did it watching TV during the adverts, it’s pretty mindless after a while.

As for transplant shock, cutting root bound roots is common practice, I’ve done it.
Let’s imagine a single spiral root that is say 1 ft long and the blade cut it in half, in real life it’s luck-of-the-draw where it is cut.
The end nearest the plant has to repair significant root damage and the nutrient supply is halved because half the root is missing. If the cut is close to the plant stem, then transplant shock could be significant. The root tip auxins are stopped so more roots can grow. Some plants get over it quickly, others take a week or so to recover, my tomatoes and squashes are pretty fussy about being transplanted.
By using a smart pot, there is no roots to cut, the nutrient uptake is practically unaffected so the transplant shock even in a ‘sensitive’ variety is negligible.