High tunnels -- extending your growing season
local food systems and small farms educator,
University of Illinois Extension
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With the current drought conditions,
you are probably not thinking about winter growing, but for both
market gardeners and home gardeners, high tunnels can provide winter
production of fresh vegetables.
High tunnels, or hoophouses, are unheated greenhouses that can
help you extend your growing season. High tunnels differ from
greenhouses in that they are less expensive. Greenhouses can
cost up to $20 per square foot to construct, while high tunnels
can cost as little as 50 cents per square foot. Greenhouse
structures may be covered with glass, rigid panels or double
layers of plastic, but high tunnels are usually covered with a
single layer of plastic.
What are some of the attributes of high tunnels? The
dimensions of high tunnels are tall enough to walk in
comfortably, and they are typically in the range of 14-30-feet
wide by 30-96-feet long.
One obvious benefit of growing in high tunnels is that they
are used to extend the growing season. Most high tunnels are
passively ventilated via roll-up sidewalls and end walls that
can be opened or removed. Crops can be grown with no additional
Row covers used within high tunnels provide additional
protection from cold temperatures. These covers are made of a
lightweight, spun-fabric cloth that is placed directly above the
crops on a supporting framework. In general, a single layer, the
poly on the high tunnel, provides one hardiness zone of
protection, and a second layer, the row cover, will provide
another zone of protection. Crops grown in zone 5 with two
layers of protection are approximately equivalent to zone 7 as
far as winter hardiness in concerned.
Crops in high tunnels are typically grown in the ground, and
they must be irrigated because rain cannot enter the structure.
Drip irrigation is often used. Watering frequency varies during
the winter but should occur often enough to prevent plants from
wilting. Even during the winter, monitoring soil moisture is
necessary, and watering intervals will have to be determined
based on conditions in the high tunnel, the soil type and
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Some of the crops that can be grown during
the winter are baby-leaf (mesclun) salad, carrots, leeks,
spinach, māche (corn salad), radishes, onions, scallions,
watercress, beets, potatoes and turnips.
If you want to learn more about high tunnel growing, I would
recommend several books, including "Four Season Harvest: Organic
Vegetables from Your Home Garden All Year Long" and the "Winter
Harvest Handbook," both by Eliot Coleman; "The Hoophouse Handbook,"
by Lynn Byczynski; and "The Polytunnel Handbook," by Andy McKee and
Mark Gatter. I would also suggest that you check out these websites:
Lastly, I would like to share information about an upcoming
webinar, "A Harvest for All Seasons," that will provide you with
information on how to take advantage of sunlight to grow crops
year-round. The basics of vegetable variety selection, planting
considerations, watering and harvest will all be covered.
The time to think about winter high tunnel production is now.
Greens, roots and other crops can all be grown and harvested through
the winter in this climate. Attend this Web program and find the
knowledge and inspiration you'll need to eat, grow and sell more
produce throughout the year!
"A Harvest for All Seasons" will be delivered via webinar on Aug.
9 from 6 to 8 p.m. For more information and to
[By DEBORAH CAVANAUGH-GRANT, horticulture
University of Illinois Extension, Logan-Menard-Sangamon Unit]