The science behind Carson City’s Greenhouse Project

When organizers formed the Greenhouse Project 10 years ago in Carson City, their vision was to establish a sustainable program that provided wholesome, natural produce to the community.

What Carson City has benefited from over the past decade is exactly that.

Both the main greenhouse site off Robinson Street behind Carson High School and the newer Foothill Garden behind the Carson Tahoe Cancer Institute off Medical Parkway employ renewable practices to grow flowering and fruiting plants.

“Agro-ecology is a more advanced term for sustainable agriculture,” said Greenhouse Project Assistant Manager William Pierz, who tends the Foothill Garden hoop house behind the Carson Tahoe Medical Complex. “We are actually trying to create a full-on ecosystem that, with just a bit of management on our end, really takes care of itself.”

Foothill Garden has to be managed a bit differently from the main greenhouse at the center of town, Pierz said, because crops are grown in native soil rather than in raised beds. This is an added challenge for horticulturists given the qualities and deficiencies of high desert dirt.

“The sand, silt or clay base has all of the nutrition, all of the micro-nutrients that plants could need,” Pierz said. “As long as we manage our nitrogen cycle, and keep the soil biology happy and diverse, the plants will be very strong and very healthy.”

So far, so good. The first crops at Foothill Garden, which opened in July 2017, were harvested this past December. Spinach, mustard greens, radishes, turnips, heads of cabbage and some broccoli ripened in the hoop house over the fall season.

Greenhouse Project Manager Cory King said estimates right now are that Foothill Garden could produce about a quarter of the total yield at the main greenhouse site, which averages between 2,000 and 3,000 pounds of produce a year.

“There's a lot of value to growing in the ground,” he said. “There are advantages to this, but our native soil has some challenges for growing vegetables.”

To make up for what the native soil lacks, Pierz said the Greenhouse Project uses compost from Full Circle Compost in Carson City to promote soil biology and organic matter.

“Our native soils have a bad reputation,” he said. “But aside from being heavy clays, the only thing really wrong with them is that they are low in organic matter. So we need to bring that back, and we do that by incorporating the compost.”

Pierre said the Greenhouse Project also does not employ soil tillage, which can disturb the soil biology. The idea behind sustainable agriculture, or agro-ecology, is to encourage plants to take care of themselves.

“Our no-till, non-mechanized methodology is using plant roots,” he said. “They take sunlight, along with a little bit of water, and then they put the organic matter down into the soil via the root zone.”

When crops are harvested, they are cut down level to the soil rather than tilled, then dressed over and transplanted.

“By using the roots, it keeps the soil biology undisturbed, particularly the fungi,” Pierz said. “That fungi assists the plants in obtaining nutrients mined from the mineral base. In exchange, the sugars produced by plants via photosynthesis feeds the fungi and other micro-organisms in the soil.”

Fungi, and especially mycorrhizal fungi, assist plants with nutrient uptake and a healthy immune system, he said. But they are very susceptible to tillage.

“It destroys their structure, and they take a while to bounce back,” Pierz said. “By keeping that fungi intact, we are giving our plants the best chance to take care of themselves without additional fertilizers. They use most of what they trade for to grow themselves.”

Pierz said there are three guiding principles to sustainable agro-ecology.

The first is to minimize tillage and its disturbance of the soil. Second is to maximize the diversity of plants, insects and organic matters in the soil, because those promote ecosystem resiliency. And third is to keep the soil armored at all times.

“We always keep our soil mulched and covered, because that not only holds in moisture, but it prevents compaction and provides habitat for the good insects,” he said. “We are only taking from the soil what we are harvesting and donating. Then we will give that back to the soil through the incorporation of compost.”

Plant diversity inside of the green and hoop houses helps grow the habitat for beneficial, predatory insects that eat the pests, Pierz said.

“That's how we get away with not using pesticides,” he said. “We have blocks of flowering plants and other random plants tucked around the leafy greens. That provides food for these insects when there are no aphids or other pests to eat.”

Crops are also not grown together all in the same area of the green or hoop houses, King said, in order to discourage and confuse pests that like to feed on specific plant matter.

“It's better to have a mixture of things that trick the pests,” he said. “When they get confused about where their favorite food is, then we can get the upper hand.”

Outside biology is also minimized by the use of insect netting on the exterior of the hoop and greenhouses.

“What we're trying to do in this greenhouse is produce a lot of variety,” King said. “Some things work better than others when you are growing them together.”

At the main one-acre horticulture site tucked behind Carson High School, a state-of-the-art 2,100 square-foot greenhouse was constructed 10 years ago to maximize crop yield while minimizing its footprint on the environment.

A cluster of solar panels helps provide electricity to run the fans, blowers, and pumps that keep the temperature steady and the climate controlled.

“The solar array here helps a lot with our energy costs and is a big part of the operation,” said King, who manages the main site, “especially in the winter time when we are using a lot more electricity anyway.”

Temperature of the indoor environment is kept at between 60 and 85 degrees to accommodate the variety of plants being grown inside.

“We're growing tomatoes and cucumbers in there that are a little bit more finicky with temperature,” King said.

To ensure winter time temperatures can be maintained at a level comfortable for sensitive plants, a ground source heat pump was installed at a cost of $30,000 when the site was constructed. The pump helps naturally regulate internal temperature and prevents it from fluctuating too much in the winter time.

That pump runs below ground underneath the parking lot and is fed into the greenhouse, where a constant temperature of 59 degrees can be maintained just from ground source heat.

“It exchanges that temperature in the greenhouse through a machine,” King said. “Somehow it accelerates up to 90 to 100 degrees. When it's coming out of the vents, it's actually that warm.”

Back up gas heaters are used as supplemental systems, but only very rarely, King said, turning on about once or twice during the winter.

“We're able to keep things even with that ground source heat pump,” he said.

But when temperatures start getting too warm inside the greenhouse, King said an exhaust fan switches on to help extract the heat from within.

A water wall, or evaporative swamp cooler, located at the rear of the greenhouse also runs during the summer time to help keep plants cool.

King said the project hopes to add a misting system to the greenhouse this year to help improve humidity for the plants that require more moisture in the air.

“We are storing the water, because we are using a reverse osmosis filter in order to feed super clean water into the misting system so it won't clog up,” he said.

Air circulation is a crucial part of the science to keeping temperature and climate steady inside of the greenhouse, King said.

“You get a current that's going around,” he said. “It's about mixing the air so you don't get pockets of warm temperatures, cool temperatures or carbon dioxide pooling up in one place or another. It's distributing air flow and humidity to the plants.”

The bottom line, King said, is to find a happy medium for the plants inside of the greenhouse during Northern Nevada’s climate extremes.

“In the summer time we're trying to make sure it's not too hot in here and in the winter time, it's not too cold,” he said.

Visit the Greenhouse Project web site or its Facebook page for more information and to get involved as a sponsor or volunteer.