All through the winter, Sandy Charles keeps a pair of shorts, T–shirt and a pair of flip-flops in a corner of her high-tunnel greenhouse on Filari Farm in northwest Fort Collins. And if she works among her rows of greens for more than a short time, she’s soon warm enough to shed her winter clothes.
Charles prefers the term “high tunnel” to greenhouse because, she explains, her 20- by 40-foot enclosure is not externally heated. Instead, it is heated in winter and cooled in summer by air that travels through a series of underground tubes, part of a subterranean heating/cooling system.
Now completing her fifth winter growing season, Charles supplies fresh greens all year long to her own family, 20 to 25 regular customers and to the Food Co-op and Food Bank when supplies are plentiful enough. She grows 10 types of lettuce, three varieties of arugula, five kinds of Asian greens and four herbs. By trial and error, she has discovered that during the cold months, seeds get a better start under powerful fluorescent lights in the basement of her home. Every couple of weeks she plants 80 or so seeds that she’ll transplant into her high tunnel after they’ve gotten a good start.
When Charles began extended-season gardening nearly five years ago, she brought to it a great passion for providing people with locally grown, fresh produce plus many years’ experience with farming and landscaping. In addition to living on a farm west of town where she planted, grew, froze, dried and canned everything she could, she and her husband operated a landscaping business for 27 years. “My training has been hands-on,” she said.
When her brother, Dennis Vanderheiden, bought land northwest of Fort Collins, Charles helped him plant his garden. Then Charles and a friend established their own garden on the property and embarked on a community supported agriculture project. When her partner quit the business, Charles decided to experiment with intensive gardening with the goal of creating a continuous food-producing system. She received a three-year grant from Colorado State University to help with expenses and encourage her to record information helpful to the extended-season gardening movement. One of her goals was to discover whether such a project could be commercially viable.
“Fresh greens are a valuable commodity in winter,” Charles said. “In Denver, they sell for up to $16 a pound. I keep my prices considerably lower than that.”
Making use of free plans she found on the internet (Sunnyjohn.com) she and Vanderheiden constructed a 20- by 40-foot framework for a building covered with heavy-duty 6 millimeter plastic sheeting and an inflated roof of the same material which adds to stability and insulation qualities.
Constructing the subterranean heating and cooling system required digging deep to install three layers of sleeved and perforated French-drain pipe — 27 lengths at 1-foot intervals, to control air temperature through the growing space. In winter, warm air from the surface flows underground keeping the soil from freezing. In summer, cool air from underground flows up to lower the surface temperature.
Electricity used to power fans that keep the air constantly circulating costs about $15 a month. Emergency space blankets cover the north wall of the tunnel and are an inexpensive way to provide reflected sunlight during short winter days. Blue board that is 2-inches thick surrounds the bottom of the structure like a baseboard and is embedded at a slant underneath the surface of each corner providing a frost-free foundation. Charles estimates the original cost of the structure, including labor, at about $7,000.
She lives 7 miles from the high tunnel and does not tend her plants every day. If she lived on the property, she says she’d spend time every day adjusting, covering and uncovering plants, but she is pleased that they survive without such intensive care. However she does watch temperature predictions carefully, harvests weekly, makes frequent new plantings and is conscious of the need to provide humidity to the plants.
“Because the soil is in use year-round, fertilizing is important,” she said. She keeps it organic using applications of compost tea, kelp and a fish emulsion.
She first selected appropriate plants for the tunnel using a list suggested by Maine organic gardener Elliott Coleman. Lately she’s been expanding to an Asian green, yukina savoy and claytonia, a small green leaf that has a slightly sweet taste, is particularly cold resistant and reseeds itself easily.
In a further effort to experiment, Charles built a second greenhouse, but without the underground piping. Half the newer structure has a frost-free foundation, the other does not. The halves of the building are divided by plastic sheeting. Charles has found that the portion of the building without the frost-free foundation does almost as well as the other half. She has records to show that the temperature in the second building is significantly lower because the underground heating/cooling system is absent. Even so, greens are surviving and the spinach seems to be thriving in the cool temperatures. Charles has a second CSU grant that monitors progress in her second structure.
With the arrival of spring, some of the greens in her high tunnels will need to move over. With the sidewalls open to the outside, a profusion of vegetables will sprout, protected from excessive heat, hail and wind, and in soil tailored to suit their needs.
When summer comes, Charles will don her shorts full-time and work alongside participants in the Larimer County Conservation Corps. Every morning for a month, teens between the ages of 14 and 16 will provide welcome help.