From Limited Space
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The Grow Box on the right is 30 cm long, 20 cm wide and 20 cm high. It grows 6 plants, 3 on each side. This grow box is stacked 17 times on the shelves built from 2x4 lumber as shown on the side. The 17 shelve structure grow102 plants. Each plant produces equal vegetables or more than a plant grown in fertile soil. The stack foot print covers less than one tenth of a square meter, which is less than the space needed to grow a plant in the ground
The stack height is 340 cm. This is lower than a one-story building. You can reach its top with a short ladder. Many growers go up several stories high. This is always possible with proper support against wind.
Depending on what you grow. Lettuce for example can be harvested in 30 - 45 days depending on its variety. Some radish varieties like Cherry Bell can be harvested in 22 days. Spinach and other leafy greens need 35 to 45 days. Most container growers produce 365 days a year using repeat growing cycles.
Since there is no limit on expanding upward you practically can grow unlimited number of plants in the place normally used for one plant..
In order to maximize the number of plants within a reasonably low height commercial growers use shallow containers and closer shelves. Three to four inches gap between the shelves is sufficient to allow plants to angel out to the sides and receive the needed sun exposure. When growing in vertical stacks growers use float valves to maintain nutrient levels. This is explained elsewhere in this website.
Nutrient in the containers should be allowed to go down to 3-4 cm above container's bottom. The float valve releases nutrient liquid allowing it to rise up to 5-6 cm above container's bottom. This way most of the uncovered parts of the roots remain exposed to air to absorb oxygen
It is essential to keep at least half of the roots exposed to air. After much of the roots have been uncovered they got used to receiving high amounts of oxygen. Depriving the roots from receiving most of these oxygen amounts suffocates the plant and likely to kill it.