Page 59 - Summer 2019 Journal

and there that while field growing is important, it just doesn’t compare to protected growing spaces. Even better, technology is making such spaces more productive, more efficient and easier to manage than ever before.
FROM WALLS TO HIGH TUNNELS
The original protected growing spaces were walls—yes, walls! Historically, large walls not only helped break up wind but served as heat sinks, capturing the sun’s energy during the
day and protecting the plants close to the walls and in enclosed court- yards at night. In old Louisville, many peo- ple don’t understand that the backyards with tall, beautiful brick walls that they see are a throwback to a time when such houses still engaged in some level of food production.
Greenhouses
started coming into
vogue when glass be-
came more affordable,
especially in northern
countries. Currently, a
number of Nordic coun-
tries are the world’s leaders in protected-space produce production,3,4 even though they all sit at higher latitudes than Maine! What this means is that, across much of the United States, there really isn’t a reason not to localize and extend vegetable production to most of the calendar year.
Greenhouses tend to be more permanent structures or buildings that include heating and cooling systems; while they usually are made using glass or polycarbonate-type panels; increasingly, many are also using plastic (see Table 1).5 The invention of clear plastic (both sheet and panels) and tubular metal piping allowed the birth of the modern high tunnel. Although plastic poses a perennial environmen- tal challenge in so many other ways, it solved the problem of how to make protected growing spaces both sustainable and affordable.
SUMMER2019
High tunnels are almost always covered with plastic, though some may use polycarbonate panels for the endwalls. A high tunnel is generally more of a temporary structure—not built to the same structural strength as a greenhouse. Given their ease of construction and relatively low cost (you can DIY build a two-thousand-square-foot structure for around fif- teen hundred to twenty-five hundred dollars), thousands of high tunnels are built in the U.S. every year.
In the past, the approach to heating and cooling represented the key difference between greenhouses and high tunnels: growers used active, controlled methods for heating and cooling greenhouses—relying on modern heating, ventilation and air conditioning (HVAC)—whereas
the inside environ- ment of high tunnels was controlled using passive strategies such as solar gain, venting, sidewall curtains and the like. This distinc- tion has become less pronounced over the past fifteen or so years, however, with many tunnels now using supplemental heating and cool- ing systems as well. As a result, people often use the terms “greenhouse” and
“high tunnel” inter- changeably. (For the remainder of this article, I will refer to high tunnels.)
HOW MODERN TECHNOLOGY CAN HELP
There are significant challenges to managing high tunnels well. For
instance, a winter day in Kentucky might start off well below freezing, in which case the high tunnel would need to be closed up tight for the night; some crops might even need additional protection from the cold. That same day, however, the outside temperature might reach forty-five degrees and full sun by lunch time, pushing the tunnel temperature up to seventy-five degrees or warmer in under two hours—if the outside temperature later climbs into the sixties, the tunnel, without venting, could easily hit the ninety-degree mark. If you are home all the time, no problem. You can open doors and vents and sidewalls, or close them as needed. But is everyone always home? Nope, not even farmers!
Fortunately, modern technology makes it easier than ever to meet plants’ needs in a high tunnel environment. Plants’ four basic needs are water, air, an amicable temperature for the crop in question (which generally means additional heat) and nutrients, including the microbial community that allows plants to access the nutrients. Enter modern
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