My theory is that the principle factor with regard to plants doing betting in larger containers (hence, more potting mix per plant) is not the size of the container (volume quantity of mix)but the chemical concentration level of nutrients in the potting mix.
Since hydroponically grown plants can become very big with a very small root ball in a very small container with virtually no long roots. Why, because the nutrients are efficiently supplied to the roots as the plant needs it. So, logically, if you could keep the nutrient concentration in your potting mix at the right level, the plant will get all the nutrients it needs without the nutrients having to necessarily be dispersed in a large container. If the plant gets the nutrients it needs when it needs it, not more, not less, then the plant will grow as it is designed to grow.
While my second and third flower trusses were killed off this year by the hot spell in June, my experiments are going OK now. What my data shows is that the plants with the most potting soil are generally doing better than the lesser amounts. I have provided virtually the same amount of nutrients in all the pots, large and small, therefore the concentration (per cubic inch) of nutrient chemicals is 50% to 60% less in those larger containers. Also, the containers with a fert strip and the containers that are being periodically fed are also doing well which supports my contention that the per cubic inch of soil nutrient concentration could be a factor.
The quantity of nutrients that I have put in all the pots (those not periodically fed) is a bit excessive, as it turns out. The smaller pots are yielding plants with very leathery leaves and are not recovering from the hot spell as well as the peridodically fed and fert strip plants. BTW, the plant that is doing really well is in the bigger SWC at 6.3 gallons of mix, where as the plants that are not doing so well are in the smaller SWCs with 3.5 gallons of mix. The periodically fed plants are in drip irrigated buckets with 4.5 gallons of mix. The mix in the 4.5 gal and 6.3 gallon of mix containers have a much, much lower nutrient concentration per cubic inch than the 3.5 SWCs by over 50%.
On another note, my data is showing that holes in the pots for air root pruning (both SWCs and drip irrigated pots) do better than the pots with no holes. Fert strip plants doing better than ferts mixed-in-the-mix pots. Pots with indirect sun do much better than plants only in direct sunlight. Tomato plants in fert strip pots doing better than periodically fed pots and much better than fert-in-mix pots.
I feel confident in 'my theory', but the proof will have to wait for next years experiments. Next year I will test for nutrient quantity variations specifically.
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