Ideal temperatures

Added on 07 June 2023

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A research project at a southwestern Ontario greenhouse has found a sustainable method to cool the water that growers use to irrigate their greenhouse vegetable crops — improving both plant health and fruit quality in the process.

Using funding from the Greenhouse Competitiveness and Innovation Initiative (GCII), Under Sun Acres Inc. has identified that water from a greenhouse’s stormwater management pond can be used to bring irrigation water to the ideal temperature the crops need, as opposed to using an electric or gas-powered cooling unit.

Irrigation water used for greenhouse crops is a combination of fresh water from natural sources such as wells and ponds, municipal sources, leach water that is disinfected and recirculated from within the greenhouse environment, and fertilizer. The ideal temperature for irrigation water is approximately 20-22° C [68-71.6° F] throughout the growing season.

“Growers mix fresh water from the municipality with treated leach water to use for irrigation, but when it is 32° C [89.6° F] in the greenhouse in the summer, the treated leach water is the same temperature,” explains Lucas Semple of Under Sun Acres Inc. “As you lower the temperature of the irrigation water, it increases the health of the plant by reducing plant stress.”

A lot of greenhouses, including Under Sun Acres, already use water from their stormwater management ponds to cool the fresh water they get from municipal sources, but they have no control over the temperature of the treated leach water. Its temperature would stay high no matter how much the municipal water was cooled unless they use cooling units.