High tunnels are hoop buildings that growers typically use to help extend the growing season. This is especially important in areas, like ours, where much of the year is too cold to grow vegetables and fruit without the assistance these buildings provide. They can be an important tool for farms that seek to follow the principles of agroecology.
Most people who utilize high tunnels consider the ground in those structures to be extremely valuable and they work very hard to optimize returns. That sort of pressure might push the grower to lose sight of the bigger balance sheet that measures more than yield and profit.
Emphasizing plant diversity in the high tunnel
We dedicated ourselves to finding ways to introduce diversity into our growing systems at our farm from the beginning. However, we also needed to find a balance with efficient growing practices so we could have sustained success as food producers. The commitment to diversity has helped ensure long term success while our search for workable growing alternatives enabled reasonable short-term returns.
It took us a few years to finally settle on a high tunnel crop rotation plan that works well at our farm. We divide the ground in Eden (one of our high tunnel’s names) into five “beds.” Each bed is big enough to allow multiple growing rows and we have identified crop pairs that complement each other.
These crop pairings were often selected because they have complimentary space needs and/or growth periods. For example, we start lettuce and tomatoes together in one bed. The lettuce and tomato root structures occupy different zones in the soil. As the tomatoes grow, they provide shade for their companions. The lettuce is harvested just before the tomatoes get too big to share the bed. Now, the longer season plants have all the space they need.
Some crop selections use knowledge of how plants interact to potentially mask their companions from pests. Other pairs give us an opportunity to move to the next crop in the bed at the right time. Carrots and beets are typically harvested early enough that we can put in a lettuce crop for late fall or early winter. Once the lettuce is harvested, that same bed will be ready for an early season planting of snow peas the next year.
This plan allows us to implement a crop rotation from one bed to the next. This prevents us from falling into the trap of growing similar plants in the same spot year after year. Crop rotations help to prevent the build-up of disease pathogens, reduces the depletion of nutrients, and discourages pests.
But our main motivation is that we know the healthiest ecosystems are diverse ecosystems. Healthy ecosystems tend to take care of themselves. Disease and pest pressures are lower. Soil health is higher. Plants are healthier.
And production of the food crops is consistently good.
The problem for a food grower is finding the balance between diversity that supports that health while making it possible to build an economically sustainable food producing farm. I’m here to tell you that it can be done and it’s a worthwhile puzzle to solve.
Melons in the high tunnel – 2010
Fighting the economic pressure
Putting up a high tunnel can be a significant investment for a small-scale, diversified operation. This often leads growers to seek rapid returns in an effort to pay for the construction costs. A common approach used for high tunnels has been to select one or two high value crops and focus on their production inside the building.
Our first year with a high tunnel was a difficult one for us. We had significant and unrelenting rainfall through the month of June that destroyed many of our crops. Our high tunnel was put up in July and we used it to try and get a melon crop in a year where our first attempt had rotted in the field. Aside from a few different tomato plants along one side, the only diversity we offered was in planting three varieties of melons.
As you might expect, we had more pest pressure than we usually experienced. But we still had sufficient success – helping to salvage what was looking like a lost season.
Another farm we are acquainted with filled their high tunnel with lettuce early in the year hoping to fulfill a bulk sales contract. They followed the lettuce with tomatoes, running that production as late in the year as they were able. Someone else grew only tomatoes—heating the high tunnel early in the year in attempt to make sales earlier than anyone else during the season.
Sadly, these approaches mirror single crop (monocrop) models that adorn the landscape each year in states like Iowa, where I live. Small-scale growers like to say they are better than the corn and soybean growers, but they also find it is hard to ignore pressure from the economics of the dominant food and farming systems pushed by corporate interests.
Even these small farms can fall prey to the temptation that it’s all about the highest crop yield and monetary returns for this season. It can be very hard to think long-term when the sweat dripping from the tip of your nose today is because of the crop that is in front of you.
But it doesn’t have to be that way.
Crops after high tunnel moved off of them – 2021
Soil health matters in a high tunnel too
High tunnel growing systems do bring challenges with them. Intense and persistent crop production inside these structures can harm soil health. In fact, growers always need to remember that the two things that harm the soil the most are frequent soil disturbance (tillage) and and the persistent use of pesticides.
Many successful high tunnel growers use various mulches, such as straw or grass, to cover the soil. A few have even figured out how to incorporate living mulches into their systems. Since these are not synthetic products, they break down over time and add nutrients to the soil. Other growers have successfully added cover crops into their rotation. These plants can be turned back into the soil to replenish organic matter.
Our farm opted to construct mobile high tunnel structures. Each of our two buildings can be moved between two positions using a system of rails and wheels. This allows us to expose the soil to the natural filtration of water and the cycles of frost and thaw. When the building is off of a position, it becomes easier to add composted manure and grow cover crops.
We could even let some chickens run around in that plot if we wanted to let them spread manure for us.
We can also start certain crops earlier than usual and then move the building off of them to complete their growth. Shown above is a rotation that features snow peas, potatoes, green beans and lettuce that has just been uncovered. As these crops are harvested, we replace them with a cover crop which will die during the following winter.
Nature terminates the cover crop. The residue keeps the soil covered during the cold months. That plant residue breaks down naturally and feeds the soil. That sounds like a winning strategy to me.
Preparing to move a high tunnel
Agroecology — embracing complexity with high tunnels
With Earth Day approaching, it seems like an excellent time to remind myself (and you) that Mother Earth is a supremely complex place. Agroecology recognizes that and embraces her complexity — both in nature and in our communities and cultures. When we are successful in working with nature as a partner, rather than an adversary, we create places where our hearts tell us we belong.
That’s when we’ll know we have found success, because a successful field, or high tunnel, is one that we want to be in.
While the systems and techniques that my farm has adopted introduced some inefficiencies from a single season yield or profit standpoint, I feel that the overall balance is good. By prioritizing diversity and soil health, even in our high tunnels, we are doing our best to navigate a working partnership with nature. In return, nature provides services like nutrient cycling, natural predation and pollination (among others) that make food production possible.
Now we need to adjust our social and economic systems to support agroecology so these practices are the norm, rather than the exception. That’s a project we can all engage in together. But for now, you must excuse me. I’ve got some planting to do.
