A Low-Carbon Citrus Greenhouse in Canada


Growing Subtropical Fruit with Minimal Inputs for Heat, Water and Nutrients

      
by BC Farms & Food  -  Permalink
May 7, 2019

On Salt Spring Island, in Canada’s Pacific maritime climate, oranges and avocados flourish in an innovative, energy-conserving greenhouse. The subtropical fruit greenhouse, called simply “The Garden,” uses renewable energy, thermal mass, nutrient cycling, and rainwater harvesting to grow citrus fruits with minimal inputs. (Article continues below video.)

Video: Growing a Sustainable Citrus Garden in Canada

Jane Squier owns and cultivates the 6,000 square-foot greenhouse as part of her three-acre farm. Apple, cherry, almond, peach, pear, plum, and pomegranate trees, along with kiwi vines, grow outdoors on the property. The remainder of the farm is devoted to vegetable and flower gardens, water catchment pools, and two acres of forest.

A stone pathway leads through subtropical fruit trees at The Garden, a citrus greenhouse on Salt Spring Island, BC. A Low-Carbon Citrus Greenhouse in Canada.

Inside the Citrus Fruit Greenhouse

When you enter the greenhouse at The Garden, you’re immediately transported to a Mediterranean climate. The air smells of earth, fruit trees, and fragrant blossoms. Fruit, hanging wherever you look, gives a feeling of abundance.

Walking the narrow stone pathways, you pass 40 varieties of citrus—oranges, lemons, grapefruits, kumquats and limes. Avocados, pineapple guavas, loquats, figs, jujube (red dates), olives, turmeric, ginger, and cardamom complete the tour. The trees arch up to the ceiling, making a canopy of green above and around you. The different leaves and fruits of so many varieties of subtropicals create a remarkable visual texture.

A lemon blossom. A Low-Carbon Citrus Greenhouse in Canada.A ripe orange on the tree. A Low-Carbon Citrus Greenhouse in Canada.

A ripening kumquat on the tree. A Low-Carbon Citrus Greenhouse in Canada.

In the citrus greenhouse: a lemon blossom, Roberston naval orange, and Centennial kumquat

The Challenge: A Low-Carbon Citrus Garden

Originally, Jane grew hydroponic lettuce and basil commercially in the greenhouse. In 2014, after much planning, she began to convert most of her indoor growing space into a perennial subtropical fruit forest. The challenge was to create a citrus greenhouse that could run almost entirely on sustainable heat, water and soil nutrients.

Heating the Greenhouse: Renewable Energy and Thermal Mass

Salt Spring Island sits in the warmest plant hardiness zone in Canada (zone 9). Although, temperatures rarely go below -4ºC (25ºF), cold winter weather can prove fatal to subtropical fruits. In general, citrus fruits grow best at temperatures above 13ºC (55ºF).

Jane decided to heat the greenhouse with a high efficiency wood gasifier furnace. The outdoor furnace burns locally-harvested wood equal to the amount generated by the forest on her property.

“I did a calculation on the sustainable yield of my two acres of Douglas fir here,” said Jane, “and that came out to about three cords of wood. So, I thought, I’ll shoot for that amount.”

Her wood furnace heats water and hydronically channels warmth into the greenhouse. A 4,500 gallon insulated pool in the greenhouse stores hot water, decreasing demand on the furnace during cold weather. Hyperadobe earth bag walls and retractable energy curtains conserve energy. As a result, the temperature in the greenhouse rarely drops below 4ºC (39ºF), even in the coldest weather.

A large insulated pool in the greenhouse, surrounded by thick hyperadobe walls. A Low-Carbon Citrus Greenhouse in Canada.

A large insulated pool in the greenhouse stores hot water to help decrease the demand on the furnace. Thick hyperadobe walls, built using the earth dug up when planting the trees, provide thermal mass to moderate the temperature. Above, an energy curtain provides additional insulation.

Water Harvesting

Water on Salt Spring Island is expensive, not available in great quantities, and subject to restrictions during recurrent droughts. To deal with this shortage, Jane decided to rely entirely on rainwater harvesting for the farm’s water needs.

Large plastic swimming pools used for water catchment. A Low-Carbon Citrus Greenhouse in Canada.

Large plastic swimming pools store rainwater harvested from the roof of the greenhouse. Rainwater catchment supplies the greenhouse with water year-round.

“For the last 18 years, it’s been full rainwater production on everything,” Jane said. That includes the greenhouse, the gardens, and even some of her household needs, such as drinking water and showers. To supply her horticultural water needs, she collects 60,000 gallons (270,000 litres) of rainwater each season from the roof of her greenhouse. The rainwater flows into four lined plastic swimming pools for storage. This provides water to The Garden throughout the year, including the dry summer months. After cleaning at the end of summer, new rainfall recharges pools by November.

Methane Digester: Waste into Fertilizer

Tanks and a digestate collection bucket which make up part of the anaerobic digester at the farm. A Low-Carbon Citrus Fruit Greenhouse in Canada.

The anaerobic digester recycles kitchen and garden waste into nutrients for the soil.

With water needs met, Jane turned to fertilizer. “I was trying to look at how I could turn the waste from my farm into a nutrient solution. How could I recycle the nutrients?” After experimenting with vermiculture and nutrient solutions, she learned about anaerobic digestion.

To turn kitchen and garden wastes into fertilizer, Jane commissioned an engineer to design and build an small-scale automated anaerobic digester on the property. Anaerobic digestion by bacteria takes place in a sealed, oxygen-free tank, and produces methane and CO2. Jane uses the methane for cooking, and to pasteurize nutrients for the greenhouse. She also pumps the CO2 into the greenhouse to accelerate plant growth in the winter. The remaining nutrient-rich solids (digestate) make an excellent fertilizer for the fruit trees.

A Model for Low-Carbon Sustainable Agriculture

The Garden is a food production system designed for a 21st century agriculture, with limits on water, energy, and fertilizer.

A ripe avocado on the tree at The Garden on Salt Spring Island. A Low-Carbon Citrus Greenhouse in Canada.

One of four varieties of avocados Jane Squier grows at The Garden on Salt Spring Island.

The fruit trees grow only with rainwater. Locally-harvested wood supplies heat, using inputs equivalent to what the on-site forest can replenish each year. Hyperadobe walls and an insulated pool in the greenhouse store heat and moderate the temperature, reducing heating demands. Kitchen and farm wastes generate energy for cooking, provide CO2 enhancement for the greenhouse in the winter, and produce fertilizer for the trees.

Using this system, it is likely that Jane Squier grows citrus fruit with the lowest CO2 footprint in Canada. The Garden on Salt Spring Island is a blueprint for low-carbon farming and a model of ecological agriculture.

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2 Responses leave one →
  1. 2019 May 29
    Elizabeth Eriksson permalink

    Awesome achievement in The Garden and delightful video. Thank you!

  2. 2019 May 9
    Bob Maxwell permalink

    Brilliant woman, and a great job on the video. Who said we can’t build a sustainable world?

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