VOA3R
Greenhouse and controlled-environment growing
Climate control, screens, ventilation and vertical systems - what the equipment does, and the energy arithmetic that decides whether the crop pays for the building.
Controlled-environment agriculture covers everything from a polytunnel to a fully sealed indoor farm. The common thread is that the grower takes over one or more variables the weather would otherwise decide, and pays for the privilege in capital and energy.
Whether that trade is worth making comes down to arithmetic that is unusually easy to get wrong, because the capital cost is visible up front and the energy cost arrives quietly every month for twenty years.
What you are actually buying control over
| Structure | Controls | Does not control | Energy profile |
|---|---|---|---|
| Polytunnel | Rain, wind, some temperature | Light, most temperature | Near zero |
| Glasshouse, unheated | Rain, wind, temperature partly | Light, winter minimums | Low |
| Glasshouse, heated + screens | Temperature, humidity, CO₂ | Natural light level | Moderate, seasonal |
| Sealed indoor / vertical | Everything | Nothing | High, constant |
Each step down that table buys more control and adds a fixed cost that does not care whether the market price is good this month. The failures in this sector are almost never biological - they are the bottom row meeting a market that will not pay a premium.
Climate control is really transpiration control
Most greenhouse climate strategy reduces to keeping the plant transpiring at the right rate. Transpiration moves water and, critically, calcium into the leaves and fruit. Too little and you get tip burn and blossom end rot; too much and the plant closes its stomata and stops taking up carbon dioxide.
That is why vapour pressure deficit has displaced relative humidity as the control target, and why heating and ventilation are often run together in ways that look wasteful but are not. Greenhouse climate control goes through the equipment and the control logic.
Vertical farming, assessed fairly
Vertical farming deserves neither the enthusiasm of 2019 nor the dismissal that followed the insolvencies. It is a production method with a narrow but real economic window: high-value crops, short cycles, low biomass, proximity to expensive markets, and ideally a buyer who values year-round consistency enough to pay for it.
Propagation and plant nurseries have turned out to be one of the strongest applications, because young plants are high-value per unit of light and the uniformity genuinely matters downstream. Leafy greens work in some markets and not others. Staple crops do not work and there is no plausible route by which they will. Vertical farming sets out the numbers.
Related sections
Irrigation and fertigation under cover overlap heavily with irrigation automation. For soilless growing systems and their water chemistry, see aquaponics and soilless growing, and for the lighting specifications that apply equally in a vertical farm, grow lights.
Frequently asked questions
Why do vertical farms keep failing financially?
Because lighting and cooling are a permanent operating cost that sunlight does not charge for, and because the crops that tolerate the economics are a narrow set. A vertical farm has to beat field or greenhouse production on price after paying for every photon. That works for high-value, fast, low-mass crops close to expensive markets - leafy greens, herbs, propagation material - and has repeatedly failed for anything that needs to grow large or slow.
What is VPD and why does everyone talk about it?
Vapour pressure deficit is the difference between the moisture the air currently holds and the maximum it could hold at that temperature. It predicts transpiration better than relative humidity does, because it accounts for temperature. Controlling to a VPD target rather than a humidity target keeps transpiration and therefore calcium transport steady as temperature changes through the day.
Is a thermal screen worth installing in an existing greenhouse?
In any climate with a real heating season, it is usually the shortest-payback upgrade available. Screens cut night-time heat loss substantially for a fraction of the cost of new glazing, and modern movable screens double as shade and humidity management during the day. It is the least exciting recommendation in this section and the one most likely to pay back.