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Are fruits and vegetables grown under glass, plastic or artificial light as nutritious as ones grown outside in direct sunlight?

Tony Woodward
Portland, Oregon, US

Fruits and vegetables grown in greenhouses can be as nutritious as those grown in fields under natural light. Indeed, under ideal conditions they are more nutritious and healthier.

Greenhouses provide a constant environment without the hazards of bad weather; insufficient sunlight can be corrected by electric light. Properly maintained greenhouses don’t have the pests that can attack plants in the field and therefore don’t need the toxic pesticides commonly sprayed over fields. Moreover, in a greenhouse, plants can be given the best nutrients not only for growth, but for synthesis of antioxidants and vitamins.

A 2012 study comparing vegetables grown in greenhouses and in the field reported higher levels of micronutrients and vitamin C in the greenhouse crops. As the authors point out, the concentration of desired nutrients depends on the fertiliser provided for plant growth.

Greenhouses allow the production of vegetables in all seasons, use 10 to 20 times less land, allow more efficient harvesting and can be erected closer to the point of sale. On the other hand, they can use a lot of electricity and water.

Kellie Walters
University of Tennessee, Knoxville, US

Over the past couple of years, my lab has been focused on controlled-environment agriculture and how we can leverage environmental controls to alter plant-produced vitamins and nutrients (phytonutrients).

While we haven’t compared indoor or greenhouse-produced plants with outdoor plants directly, the main advantage of greenhouse and especially indoor plant production (think warehouse with no sunlight) is that we can precisely control the growing environment (light quantity, duration and colour, as well as the temperature, fertiliser, etc.) to elicit a desired response. That may be a combination of plant growth/yield, shelf-life, flavour or phytonutrient accumulation.

How we grow the crop influences how nutritious it is. So, one can produce a crop with low or high phytonutrients indoors, depending on the conditions. We are currently working on research to give producers/growers the tools to predictably do this.

A producer/grower can grow low or high-phytonutrient crops outdoors as well, but they can’t control the growing environment like we can indoors, so this isn’t as predictable.

Another factor that affects outcomes is how long a food crop has been in shipping, storage or on the shelf, as this also influences phytonutrient concentrations.

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