Vegetables from Mexico are better for the environment

Photo by Erwan Hesry on Unsplash

This article first appeared in Castanet Oct 29, 2024

Canada is growing more of its own food.

More than half of our fresh fruits and vegetables come from outside Canada, mostly trucked in from the U.S. and Mexico.

We can’t make our northern growing season longer but we can move production inside, into commercial greenhouses. Between 2013 and 2023, Canadian greenhouse-grown fruits and vegetables increased by 36%. The biggest provinces for greenhouse fruits and vegetables are Ontario with two-thirds of Canada’s total and British Columbia with just under 20%.

B.C.’s Fraser Valley greenhouses produce large quantities of tomatoes, sweet bell peppers, long English cucumbers and butter head lettuce (in this column I won’t be discussing flowers, which make up 50% of B.C.’s greenhouse-grown plants).

You might nod at this point and agree that greenhouses are an environmentally friendly way of extending the growing season. The glass or plastic forming the envelope of the greenhouse traps the sun’s rays inside, where they warm the environment, allowing growers to plant earlier in the spring, harvest later in the fall and provide a consistently warm environment that speeds up growth.

The problem is modern commercial greenhouses aren’t passive collectors of the sun’s light and warmth. Instead, they are large consumers of energy, drawing electricity to power lights that extend the growing day year round and natural gas to heat the greenhouse through the winter. That allows crop harvests all year round, especially during the winter when fresh fruits and vegetables are in high demand.

In Ontario, energy costs are about 40% for lighting and 60% for heating. In B.C., with milder winters, the split is close to 50%-50%. The energy problem is twofold—lighting is primarily provided with high-pressure sodium and a traditional commercial greenhouse was never designed to be heated.

If you are doing energy retrofits on your house, or designing a new energy-efficient house, you will run into a window problem. You would like large windows for a great view and lots of natural light but windows are a weak point in the efficiency of a house. Even triple glazed windows have a “u” value of 0.8. An insulated wall has an equivalent factor of 0.05 (lower is better). Now imagine living in a house where every wall and the roof is a window.

You would imagine growing fruit and vegetables in a greenhouse for local consumption would be better for the environment than trucking in food from the U.S. or Mexico, but you would be wrong. A 2011 paper by J.A. Dyer et al found Ontario greenhouse-grown fruits and vegetables generated more carbon than growing them in the southern U.S. and trucking them in by a factor of 1.7. That same paper found carbon emissions from B.C. greenhouse-grown fruits and vegetables were nearly three times higher than imported fruits and vegetables.

Work in 2020 by Taillefer and Shear at the University of Toronto found greenhouse-grown lettuce in Quebec created nearly twice as much carbon as lettuce imported from California. Extensive work in Europe, comparing greenhouse-grown vegetables in The Netherlands (which has weather similar to the Fraser Valley) with field-raised tomatoes from Spain, also found greenhouse-grown vegetables generated a lot more carbon.

One confusing issue is the argument that greenhouse grown fruits and vegetables are 10 times more efficient. That efficiency, however, is not about energy or carbon but land area. It is true you can grow more food per square metre in a greenhouse. That is an argument important in The Netherlands, with a high population in a small country, but not relevant to Canada.

As a consumer, the choice is clear, if you have a choice between winter tomatoes from Mexico or B.C.-grown tomatoes, Mexico tomatoes are the clear winner for the planet.

The question is, can we solve this problem from an agricultural point of view? Can we grow food in Fraser Valley greenhouses with lower carbon emissions? The fundamental problem with greenhouse design is the greenhouses we have, and the ones we are building today, are still designed to be passive collectors of sunlight. Architecturally, we add heat and lighting as an afterthought. Coastal B.C. with its warmer temperatures and hydro-powered electricity should certainly be able to produce a low-carbon tomato.

Articles and cartoons on Teaspoon Energy by Kristy Dyer are licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License. You may reprint this as-is for free, contact me to request changes. Images belong to the original artists.