A polytunnel protects berries from rain and extends the season, but the plastic also creates a climate that must be actively managed. Without enough air exchange, heat and humidity rise, plant transpiration changes and carbon dioxide can be depleted during periods of strong photosynthesis.
Four reasons to move the air
Richard Mills of Haygrove identifies four connected jobs for ventilation: controlling temperature, lowering excess humidity, managing crop transpiration and refreshing carbon dioxide. Each affects the others. A closed tunnel may warm quickly, but the same conditions can slow useful air movement, encourage disease and make it harder for plants to regulate water.
Fresh outside air is often a more economical way to restore carbon dioxide than injecting purchased CO₂. That makes vents more than a heat-release device; they are part of maintaining the atmosphere around a productive canopy.
Choose the level of control the crop justifies
Growers can use manual roll-up sides, mechanised openings, automated systems linked to climate readings or permanent venting. The right choice depends on crop value, tunnel length, local weather, labour and how quickly conditions can change. Substrate-grown berries may need especially close attention because the root zone has less buffering capacity than field soil.
Ventilation does not remove the need to monitor irrigation, nutrition and disease. It gives the grower another control over the crop’s environment—and helps prevent a structure built for protection from becoming a source of stress.
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When Vents in Polytunnels Make the Most Sense for Berry Crops was published by Growing Produce, drawing on guidance from Haygrove’s Richard Mills.