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The Garden Scoop

High Tunnels

At this point in fall, most of our vegetable gardens are completely done for the season, with the exception of some kale or a few other cold hardy crops.  Wouldn’t it be great to have a way to extend the growing season for a few months and keep enjoying fresh produce?  Many small farmers have very successfully done this with the use of high tunnels.  In fact, many high tunnels in our area are productive nearly year round.

If you are not familiar with high tunnels, or hoophouses, they are unheated (or sometimes minimally heated) greenhouse-type structures that enclose a growing area to protect it from temperature extremes and, in some cases, pest pressure. 

High tunnels differ from greenhouses in a number of ways, but primarily due to the fact that plants are grown in the soil, as opposed to in trays or pots of soil medium as in greenhouses.  They are typically non-permanent structures covered in one or two layers of UV resistant polyethylene plastic spanning a semi-circle of steel arches, which creates an enclosed production system resulting in protection from the elements and more stable production with less risk of crop failure.

The UIUC Sustainable Student Farm in Urbana uses three large high tunnels (approximately 30 x 96 ft.) to produce a variety of vegetables and greens each year.  “Our high tunnels are the most useful production areas on the farm,” said Matt Turino who is the farm manager at the Sustainable Student Farm.   Matt went on to explain how high tunnels were part an integral part of the farm from its inception in 2009, “Season extension is a big factor out here. We use our high tunnels all year round, with most of the harvesting occurring in about 9-10 months out of the year.”  When crops aren’t being harvested from the high tunnels, there is still much activity, from bed preparation and the planting of new crops to the installation or removal of infrastructure, like irrigation.

The versatility of high tunnels is quite amazing.  Many of these structures are built in a fixed location, but some are able to be moved along tracks.  The high tunnels at the Sustainable Student Farm are moveable, which allows from much greater flexibility in crop rotation and maintaining soil productivity.

All high tunnels have features to provide greater ventilation during the heat of the day, which helps to mitigate extremes.  In most cases the side walls can be rolled up, either manually or thru automated systems triggered by temperature or timers.  The flat end walls typically have some type of ventilation as well.  Most growers use a single layer of polyethylene plastic to cover their structures, although some use other materials, such as shade cloth.  Some growers remove the covering entirely for warmer parts of the year.

The crops grown in high tunnels very widely from annual crops, such as lettuce and greens, to perennial crops such as raspberries or blackberries. “Our main winter crops are things like spinach, lettuce, kale, and bok choy, whereas our primary summer crops are tomatoes and peppers”, said Matt. 

The staff out at the Sustainable Student farm, which includes a good number of student workers, rotate the high tunnel crops by the season.  As summer ends, tomatoes and peppers are retired and cool season crops, like lettuce and greens, are planted for harvest throughout fall and early winter.  In late winter another planting of cold hardy lettuce and greens is initiated until the weather warms up just enough to move the high tunnel down its tracks to a new location where tomatoes and peppers are started under its protection.  Matt explained how this system extends tomato planting and harvest, “Inside our high tunnels, we are able to plant tomatoes 3-4 weeks earlier than usual in spring and harvest tomatoes 3-4 weeks later in fall.”

If you would like to experiment with season extension in your own garden, you can easily build a DIY “low tunnel”.  Begin by planting a small section of your garden with some late fall or early spring crops. Bows to support the low tunnel’s semi-circle structure can be made from materials as simple as PVC pipes spaced every 3-4 ft along the planting. Floating row cover or polyethylene plastic can be used to cover the structure on cold nights and protect from frost.  With some watering and care, your low tunnel will protect plants from temperature extremes, extending the growing season in your garden.

Ryan Pankau is Horticulture Extension Educator with University of Illinois Extension serving Champaign, Ford, Iroquois, and Vermilion Counties.