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Part
I
Introduction |
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1 |
What is a High Tunnel? |
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High
tunnels are unheated, plastic-covered structures that provide
an intermediate level of environmental protection and control
compared to open field conditions and heated greenhouses
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| Cost |
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•Unlike
commercial greenhouses that cost up to $20 per square foot to
construct, high tunnels can cost as little as $0.50 per square
foot |
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•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 |
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| Dimensions |
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•High
tunnels are tall enough to walk-in comfortably and to grow
tall, trellised crops such as tomatoes
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In
contrast, low tunnels are too short to stand upright inside
and cannot be used to produce some crops
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•There
are no standard dimensions for high tunnel sizes, but they typically
fall within the ranges of 14-30 feet wide by 30-96 feet long |
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| Environmental
Control |
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•Most
high tunnels are passively ventilated via roll-up sidewalls
and end walls that can be opened or removed |
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•Crops
generally require no heat, though supplementary heat can be
provided for protection on cold nights or used to extend the
season even longer |
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•Row
covers used within high tunnels provide additional protection
from cold temperatures |
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In
general, a single layer (the poly on the high tunnel) provides
one hardiness zone of protection, and a second (the row
cover) will provide another zone of protection
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Crops
grown in zone 5 with two layers of protection are approximately
equivalent to zone 7 as far as winter hardiness in concerned.
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| Production
System |
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•Crops
are typically grown in ground beds within the high tunnel rather
than in containers |
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•Crops
grown in these ground beds must be irrigated because rain cannot
enter the protective structure |
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•Some
high tunnels are erected on skids so that the structure can
be moved during the production cycle |
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2 |
Why are High Tunnels Used? |
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| Season
Extension |
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•Compared
to open field conditions, plastic-covered high tunnels result
in a warmer production environment during late fall, winter
and early spring seasons |
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This
offers the advantage starting crops earlier in the spring
and harvesting them later in the fall
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•Production
during
the winter season is possible, but this is restricted by severity
of winter weather, what crops are grown, and availability of
supplemental heat |
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| Provide
Shade |
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•A
primary use of the high tunnel structure during the summer is
to hold shade cloth |
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Air
temperatures can be reduced by 4 degrees Fahrenheit with
30% shade
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Light
intensity reduction is appropriate in some climates and
for some crops, such as cut tulip production in southern
California and lettuce and greens production in the Midwest
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Use
of sprinkler irrigation or mist in the summer in combination
with shade cloth reduces temperatures under the high tunnels
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| Economic
Benefits |
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•During
all seasons, high tunnels provide protection from wind and rain,
which can result in increased crop yields and improved quality
as well as decreased incidence of pest and disease problems |
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3 |
Types of High Tunnels |
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| Terminology |
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•A
strict definition of a high tunnel does not exist, and the terminology
may change depending on the structure's use |
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"Hoophouse"
and "High Tunnel" are often used interchangeably
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For
example, a market farmer might grow an additional crop of
sunflowers in a "High Tunnel" after first frost,
whereas a nurseryman could over winter container-grown perennials
in the same structure but call it a "Cold Frame"
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The
same structure is also marketed to livestock operations
for animal, feed, and equipment shelter
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•Gutter
Connected High Tunnel indicates that two or more bays are
connected at the gutters |
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•French
Tunnel is the European term for a single-bay high tunnel
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•Spanish
Tunnel is the European term for a multi-bay high tunnel |
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| Photo
Gallery |
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Examples
of types of high tunnels that our project cooperators have encountered
or constructed |
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