By Hans Hansen

A question posed in the high tunnel presentation I gave at Bioneers 2014 Conference (November 2). What is a high tunnel? What distinguishes a high tunnel from a greenhouse?

The answer to this question depends on who is asked… (high tunnels aka polytunnels, hoophouses and hoop greenhouses, btw)

The simplest definition I’ve heard (or read) – “if it has roll-up sides, it’s a high tunnel…” – Texas A&M High Tunnel Seminar 2013. This explanation was given (with a grin) by one of the AgriLife Extension folks. The definition has changed quite a bit over the last couple of decades, as just about every horticulture industry that produces plants in open field and/or greenhouse settings has found high tunnel technology intriguing, therefore has experimented with it and contributed to the technology we know as high tunnel science.

Initially the term high tunnel was most commonly used in association with food crops but now it is often used with any economic field crop grown under cover in soil as opposed to containers. For example, the cut flower industry has found high tunnels to be a lucrative investment.

Early high tunnels were intended to be mobile structures that could be easily and quickly assembled/disassembled and moved from one location in the field to another.

Now, many are stationary (as is ours is at Blackwood); about the only common denominator in all high tunnel systems is that the plants in those structures are grown in soil, and of course, most tunnels do have roll-up sides. I will add that our greenhouse (container and flats only inside, brick floor) does have roll-up sides as well (it’s great technology for greenhouse producers as well).

We have narrowed the common thread down to growing crops in soil, under a flexible greenhouse-like structure, but what is to keep producers from growing, say ginger or other food crops, in portable containers in high tunnels, on a layer of woven weed fabric (as nurseries produce container trees)? Hmmmm…

An addendum to the description of high tunnels, to pull the definition out of greenhouse mindset and into that of ecological/permaculture conceptual framework. Perhaps a better way to define a high tunnel might be any or all the following combined:

– High tunnels are man-made structures that allow integration and control of key factors of (“natural”) open field and (artificial) greenhouse environments.
– High tunnels are tools for buffering environmental extremes such as intense: cold, heat, wind and light intensity.
– High tunnels are a “hybrid” of open field and greenhouse grow systems that are flexible enough that they can morph into a varied degree version of either one (e.g., sides, ends and vents are 1/8th open on a chilly day, would be mostly greenhouse-like; sides and ends fully opened = more open field-like).

In sum, a high tunnel’s hybrid nature is what defines it, is what gives it (the grow environment underneath) the capacity to morph into varying degrees of either open field or greenhouse environment, to match the grow conditions preferred by a specific plant or community/guild of plants (crops) underneath.