Introduction to High Tunnels

What are High Tunnels?

High tunnels, also called high hoops or hoop houses, are temporary structures that extend the

growing season. These covered structures are constructed in the field in order to protect crops from

the weather (rain, wind, cool or warm temperatures), as well as in some cases, pests. High tunnels

offer an intermediate level of environmental control - a growing system between row covers and

greenhouses. In comparison to greenhouses, they are unheated, provide less climate control, and

are less expensive. However, the distinction between a greenhouse and high tunnel is not always

clear; structures exist in a continuum between expensive, climate-controlled greenhouses and

inexpensive, plastic-covered PVC pipes. High tunnels are of sufficient height so the farmer can walk

through them and tall staked or trellised crops can be grown; this differentiates them from low

tunnels, although again, the distinction between low and high tunnels is blurry.

Types of High Tunnels

More permanent/expensive high tunnels

More permanent high tunnels are generally quonset- or gothic-shaped. They are most often

constructed of metal bows which are attached to metal posts, driven into the ground. They are

typically covered with one or two layers of 6-mil greenhouse-grade polyethylene, and are ventilated

by rolling up or removing the sides or ends. There are various designs each offering advantages and

disadvantages. Due to their permanent nature, care should be given to siting the high tunnel

properly.

More permanent, quonset-style high tunnel. Photo credit: Linda Naeve, Iowa State University

Extension

The quonset-style hoop house has historically been the most popular high tunnel shape due to its

simplicity. However, the circular shape limits the height at the sides of the high tunnel, limiting its use

for crop production. In addition, the quonset shape cannot easily support a snow load, so the

structure must be strengthened or the plastic must be removed before winter in regions that receive

snowfall.

More permanent, gothic-style high tunnel. Photo credit: Ted Carey, K-State Horticulutre Research

and Extension Center.

The gothic style is rising in popularity due to the problems associated with the quonset style. This

peaked design allows for greater height along the sides, making the sides of the high tunnel more

useful for crop production and resulting in a 15% greater growing space than the quonset. The peak

also sheds snowfall. In addition, the quonset shape increases the amount of light infiltration, which

results in higher temperatures and improved crop growth.

Movable/inexpensive high tunnels

Low cost, movable high tunnel. Photo credit: Tim Coolong, University of Kentucky .

In the low cost, movable high tunnel system pictured above, pieces of steel pipe with an auger-turn

at the end stabilize the PVC bows. Ropes help tighten the tunnel and improve end-wall stability. This

type of construction is inexpensive and movable (allowing for easy crop rotation), but the area

covered is relatively small and the height doesn't permit the production of tall/staked crops .

Multi-bay high tunnels

Multibay tunnel systems cover larger areas. One of the first and most popular of these is produced

by Haygrove, but other companies also produce multi-bay tunnel systems. Most multi-tunnel

systems:

cover large areas

can be moved mechanically (although many growers do not move them)

don't require leveling

are relatively inexpensive

are easily vented

accomodate field-scale equipment for field preparation and management

can support plastic film, shade cloth, or bird or insect netting

Advantages of High Tunnels

High tunnels have many uses on the farm. In cooler climates, their main purpose is to elevate

temperatures a few degrees each day over a period of several weeks. This typically results in faster

plant growth and higher yields. In climates like western Oregon and Washington, high tunnels are

also used to protect crops from the winter rains and to raise night-time temperatures during the

summer. High tunnels can also be used to shade crops, protecting them from heat and sun scald.

Regardless of the region, high tunnels help growers produce crops outside of the normal season,

thus meeting consumer demand on either end of the production curve when competition is lower and

prices are higher. The modified climate inside the high tunnels also creates the opportunity to

produce crops that can't normally grow if unprotected, diversifying the farming system. By help ing

protect crops from weather-related damage, such as sun scald, wind bruises, and hail spots, and

from pest damage, high tunnels can provide a higher percentage to top-grade fruits and vegetables

at harvest.

High tunnels can also support row covers or other materials to protect the crop from pests (insects,

wind-disseminated weed seeds, or wildlife), reducing the need for pesticides and/or labor and

producing a higher quality crop. The tunnels are versatile and can be used to produce many crops,

including vegetables, small fruits, and flowers.

This picture shows the benefit of growing tomatoes inside a high tunnel. The plastic has been

removed to show a side-by side comparison of tomatoes grown inside the movable PVC-hoop high

tunnel (on the left) and those grown outside the high tunnel (on the right). All plants are the same

variety (Mt. Crest) and were planted on the same day in late April 2008 in Johnson County, Eastern

Kentucky. Photo credit: Tim Coolong, University of Kentucky.

Disadvantages of High Tunnels

One of the primary disadvantages of the more permanent high tunnels is the fact that they are not

easily moved. Some high tunnels are engineered to be (and advertised as) easily movable.

However, they are typically not very easy to move, and many high tunnels are never moved. The

result of this is that the same crop is grown in the same location every year, or a very short rotation

is practiced. A short rotation or no rotation in vegetable production may lead to yield reductions and,

depending on the crop, soilborne disease development (see related article, Managing Diseases of

Organic Tomatoes in Greenhouses and High Tunnels). Organic growers considering high tunnel

production should have a rotation plan in place for each tunnel (this will be easier if you have many

tunnels) or devise an efficient strategy for moving the tunnels every few years. This is one reason

that growers use movable high tunnels, such as Haygrove-type movable tunnels, or the

PVC tunnels described in the related article, Low Cost High Tunnel Construction.

Another disadvantage to high tunnel production is the lack of exhaust fans for venting during hot

weather. In most regions where tunnels are used, tunnels will overheat at some point during the crop

production season unless manually vented, or unless an automated vent ilation system is used to roll

up the sides as the temperature inside the tunnel rises. On warm sunny days, air temperatures in

poorly vented tunnels can easily be 40o

F greater than ambient outside temperatures. To carry

tunnel production through late spring/early summer, which will be a necessity in many regions of the

U.S., tunnels must be designed with adequate ventilation and/or easily removable plastic.

Another disadvantage of high tunnels is that they can be destroyed by high winds, snow, and ice, as

they typically do not have the strength of greenhouse structures. Tunnels should be designed to

withstand or avoid these stresses.

PVC quonset tunnel collapsed under ice and snow load. Vinland Valley Nursery, Baldwin City, KS.

Photo Credit: Dan Nagengast, hightunnels.org

Multi-bay quonset tunnels damaged in severe thunderstorm in August of 2004. Photo credit: Ted

Carey, Kansas State University.

More permanent high tunnels can be expensive - costing as much as $2.50 a square foot. The less

permanent structures cost considerably less. Regardless of the type of tunnel, tunnels increase

production costs relative to field grown crops, so crops grown in tunnels must be able to return a

higher price, or confer some other advantage to the farmer, relative to the same crop grown in the

field.

Conclusion

For most farmers, the advantages of high tunnels outweigh the disadvantages. Thousands of fruit

and vegetable farms in the U.S. successfully use high tunnels to extend the growing season. An

organic farmer considering high tunnel production should first do some preliminary research. A good

place to begin is to read the resources listed below and the linked eOrganic articles. Next, the farmer

should develop a crop production plan for the tunnel. Whenever possible, farmers should seek

advice from growers in their region with experience growing in high tunnels.

Additional Resources

Center for Plasticulture: High tunnels [Online]. College of Agricultural Science at Penn State

University. Available at: http://plasticulture.cas.psu.edu/H-tunnels.html (verified 4 March 2010).

High tunnels: using low-cost technology to increase yields, improve quality, and extend the

season. T. Blomgren, T. Frisch and S. Moore. [Online] (n.d.) University of Vermont Center for

Sustainable Agriculuture, Burlington, VT. Available

at:http://www.uvm.edu/sustainableagriculture/hightunnels.html (verified 4 March 2010). This

guide includes organic-specific information, including organic farm case studies. There is also an

accompanying video available for purchase.

High tunnel production manual, 2nd Edition. 2003. W. Lamont. Pennsylvania State University.

Available for purchase at: http://plasticulture.cas.psu.edu/manual.htm (verified 4 March

2010). This is a conventional production guide that includes one chapter on transitioning a tunnel

to organic production.

Hightunnels.org [Online]. K-state Research and Extension, University of Missouri Extension and

University of Nebraska Cooperative Extension. Available at:http://www.hightunnels.org (verified 4

March 2010). Website describing conventional high tunnel construction and management in the

Central Great Plains.

Minnesota high tunnel production manual for commercial growers [Online]. T. Nennich, D.

Wildung, and P. Johnson. 2004. University of Minnesota Extension Bulletin M1218. Available

at: http://www.extension.umn.edu/distribution/horticulture/M1218.html (verified 4 March

2010). This is a conventional production guide that includes a chapter on organic certification

compliance.