Choosing the Right Structure for Your Protected Crops

Where do you begin when you’re ready to start growing crops under cover? There are many choices in crop protection structures and some significant differences among them, from how much space and environmental control you have to labor requirements and cost.

Matthew Kleinhenz, Extension vegetable specialist with Ohio State University, starts with three questions: What are your goals? What’s your budget? And how much experience do you have with protected ag systems?

Depending on your answers, you may be fine with a relatively simple mid-level structure (like a caterpillar tunnel). Or perhaps a permanent high tunnel will offer a better balance of protection and investment. In some cases, your production goals may justify the active climate control of a greenhouse.

Here, Kleinhenz helps break down some of the differences between various structures.

Matching Protection to Investment

Each structure carries a combination of pros and cons based on factors such as initial and maintenance costs, ease of setup and removal, proven economic potential for various crops, and management requirements. These combinations provide growers with at least one option likely to meet their needs and resources.

Terminology around structures varies widely, but here’s the way Kleinhenz describes them for the purposes of this article:

Mid-Tunnels

Mid-tunnels are relatively inexpensive, temporary structures that offer more protection and cropping options than low tunnels without the commitment of a permanent installation. They can be a good step up from low tunnels if you still want flexibility but are looking to start and finish more crops under cover, experiment with protected production, and gain experience managing a larger enclosed space.

A tradeoff (compared with going right to a high tunnel) is labor. Unlike permanent structures, mid-tunnels require more time-sensitive hands-on setup, removal, and seasonal management.

High Tunnels

High tunnels are considerably taller than mid-tunnels (up to 14 feet at the center). They rely on passive environmental control through ventilation rather than mechanical heating or cooling, with sides that can be raised or lowered. Once constructed, most high tunnels remain in place year-round while others can be moved. Regardless, protected space is always available so growers can focus on crop selection and management.

Often, Kleinhenz explains, a field grower’s first step into protected production is straight toward a high tunnel. And that’s partly because USDA’s Environmental Quality Incentives Program (EQIP) has helped make those structures more accessible. Through the EQIP, as part of the Natural Resources Conservation Services (NRCP), eligible growers can receive financial assistance to install high tunnels as a conservation practice.

But that’s not necessarily the best option right out of the gate. Kleinhenz has seen growers start with high tunnels and later realize that some production goals can be met just as effectively with less costly caterpillar tunnels. Experience also matters. A high tunnel gives growers protected space; it doesn’t manage that space for them. Kleinhenz compares it to a “huge shoebox.”

“You’ve got your shoebox,” he says, “and it’s up to you, now, to fill it and make everything happen inside.”

Greenhouses

Greenhouses provide the highest degree of environmental control, but they also require the greatest investment. Kleinhenz defines a greenhouse (regardless of the material it’s made of) by the presence of active climate control: typically heating, and often cooling and supplemental lighting. Those systems allow growers to manage temperature and growing conditions much more precisely, but they also increase both capital costs and day-to-day management demands.

Consider Your Goals First

When Kleinhenz asks farmers about their goals for protected ag, the most common responses are extending the production season, diversifying into additional crops, reducing weather-related risk, and creating a more predictable production environment.

Some growers simply want earlier tomatoes for the farmers’ market. Others want to remain in the market longer into the fall, produce crops they couldn’t reliably grow outdoors, or, as Kleinhenz puts it (rather poetically), “lessen the impacts of an uncontrolled sky.”

The good news is that there isn’t a one-to-one relationship between goals and structures. More than one option may accomplish the same objective.

Take tomatoes, for example. If the goal is simply to get tomatoes to market earlier than field-grown crops, a low tunnel may provide all the protection needed. But if the objective is to be in the market significantly earlier—or to keep harvesting much later into the season—a mid-tunnel or high tunnel becomes a stronger fit because it buffers the crop from weather extremes over a longer growing period.

Likewise, Kleinhenz says, growers looking to diversify into crops such as leafy greens may find that multiple protected structures can support those plans, with the right choice depending more on economics and management than the crop itself.

For physical protection, every step up in structure reduces a grower’s vulnerability to pests, extreme temperatures, humidity, and more, but it also increases investment and management requirements. That’s why Kleinhenz encourages growers to think first about how much environmental control they actually need and to recall that low, mid-, and high tunnels can be used alone or in combination.

For more on choosing the right structures for protected crops, continue reading at CEAgWorld.com.