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Hunter Wilson of Growers Network interviews Anthony Mollins of GroGeo about how forethought and building design can lead to highly sustainable, cost-saving growing practices.

Growing Style

Subterranean greenhouse? Explain to me!

The facility itself is built into the ground, and if there wasn’t a roof on it, you’d fall into a 12-foot hole.The walls and floor are concrete with a glass roof, which pitches towards the south. Being mostly underground helps to maintain a consistent temperature in the grow space.

The idea itself comes from permaculture. There’s a structure called a “Walipini” that is essentially a subterranean greenhouse. We had some issues with airflow at first, so we started working on version two, which is what we’re currently growing in.

Tell me about the plants

We run a perpetual harvest system, and we harvest about 250 plants a week. In total, we have around 50 different strains. We hand water our plants with teas that we brew on-site. We even grow the plants that we use in the teas. We’re growing aloe, focaccia, comfrey, marigolds, and any other plants we can get our hands on.

What media and equipment are you using?

We currently grow in organic soil and use biodegradable plugs for our clones. The plugs eventually go into the compost pile. Because we’re in a subterranean greenhouse, we do need to use supplemental lighting and light deprivation depending on the time of year.

What automation and environmental controls are you using?

Most of our environmental controls are automatic or always-on. Our facility is designed with geothermal ventilation such that fans are constantly drawing air through the ground, which stays at a consistent temperature of about 60 degrees Fahrenheit. In addition to the geothermal fans, we have a bunch of fans that circulate air throughout the facility.

What pest issues have you had?

Back when we were starting out, we accidentally bought some plants from some pretty horrible growers. The plants were covered with root aphids. We battled the root aphids for over a year, and eventually, we decided the only way to get rid of the root aphids was to flush them out. We shut the whole greenhouse down, and it got up to 160 Fahrenheit for seven days, cooking the root aphids. We didn’t have that problem anymore after that.

Nowadays, we mostly just face your standard fare of pests. If we run into issues, we quarantine the plant and then use biopesticides such as predatory insects and teas to resolve the problem.

Sustainability

How does water management work for you?

The plants use up approximately 90-95% of the water we give them. Our “secret” is that we keep the environment nice and humid so that the plants don’t need that much water in the first place. Right now, we’re in the process of tweaking our VPD with the goal of higher humidity and higher temperature. Our goal for our VPD is 90 degrees and 70% RH with supplemental CO2.

How do you utilize CO2 more efficiently?

Our facility was designed so that the CO2 has nowhere to go. The whole facility is solid concrete, and you have to take the stairs down or an elevator to reach the base level of the facility. The CO2 is kept at around 800-1200 ppm, so we’re well within safety standards for humans.

What does the electric bill look like?

When we built the facility, we considered setting up renewable forms of electricity generation. Our grow happens to be in a very windy area, which would be perfect for windmills. However, the cost would have ended up being a bit too high for our needs. Currently, we only run on a 200 Amp breaker, and we could probably survive on a 40 Amp breaker in the summer.

We’re getting charged about $2,200 a month in our electric bill for a 12,000 square foot grow. For reference, I rented my house in Tahoe to some growers, and they have a much higher electric bill for a smaller grow.

What was the cost of building a subterranean greenhouse?

It was actually very competitive pricing; it was almost comparable to building a commercial greenhouse. In my experience, Nexus greenhouses cost around $100 per square foot. Our subterranean greenhouse actually turned out to be around $80 per square foot. For us, digging a big hole and pouring concrete into it was cheaper than building an above-ground structure.

If somebody wants to grow sustainably like you, where should they go for more information?

I highly recommend any grower who is interested in our practices start reading up about permaculture. Permaculture is the core growing philosophy guiding our sustainable growing practices.

This article has been paraphrased with permission from Growers Network.

Growers Network

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