Our Geothermal Greenhouse

I have always loved to garden. Over the years, despite Colorado’s relatively short and challenging growing season, I developed a love of tropical trees, growing limes and starting plants from seed.  I extend the season and grow large tropical trees by bringing my various plants indoors for the winter.  Several years ago, it became apparent that the tropical trees, herbs, flowering plants, and other greenery needed a winter home.  The idea of a greenhouse was born.  I soon came to realize that most greenhouses require a lot of energy to maintain, something I wasn’t interested in.

I looked at solar and was intrigued but not convinced, then we discovered geothermal greenhouses for the backyard gardener, and we were sold! These greenhouses are low energy users in that they use geothermal transfers or a GAHT (ground to air heat transfer) system to heat and cool the greenhouse maintaining a constant temperature year-round.  In our area it is about 55-56 degrees.

We bought a kit from CERES Greenhouse Solutions in Boulder and began planning for the optimal site on our property.  CERES assisted with engineering the best exposure for maximum sun, wind, and snow loads for our location.  We then located a contractor to begin excavation.  The hole was quite large, our son observed that it was not too late to swap the greenhouse for a pool!

This process took a while, the start to finish was a year.  Partly due to Covid delays, partly because it is a time-consuming process utilizing numerous trades; there was excavation, pouring concrete, electrical wiring and hookups, plumbing, construction of the green house itself, surrounding landscape, entrance, and inspections.

We chose to surround ours with a wide walkway of pea gravel and a raised planting bed due to the slope of our property.  We added a stone patio out front and a few chairs and table for fun.

We bought our Blumat raised beds from Sustainable Village. They are made from  pressed paper and then supported by railroad ties and PVC tubing.  We went vertical by adding support tubes.  Everyone at Sustainable Village was helpful and generous with their time.

The watering system is also from Blumat, it’s based on a system of clay carrots dating back to Egyptian times that embed in each raised bed.  When wet they expand shutting off the water tube and when dry they constrict to allow for water flow. No electricity required.

We monitor all electronically via an Accurite system that allows us to monitor humidity, inside and outside temperatures, and a number of air transfer temperatures from our phones.  We have discovered that we need a small back up heater for temperatures below 15 degrees and have installed an evaporative cooler for the hot summer temperatures. While the GAHTS system does its job of maintaining temperature, our direct Colorado sun and overall design brings in and holds a lot of heat year-round.

After all of the planning and hard work we have an operational greenhouse that has Sonos sound, shades, lighting, and room for chairs to enjoy a cocktail or glass of wine.

As for what we are growing and currently harvesting – lettuces, kale, tomatoes, sugar snap peas, a variety of herbs, limes, strawberries, gerbera daisies and yellow daisies for cutting, and lemons, grapefruit, and tangerines to come!   It is a constant learning project, some things work, others fail.

I would recommend this fun project for every avid gardener!


~ Elyse Foster

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