Vegetable growers might consider high tunnels

Posted April 2, 2013 at 6:19 pm


Vegetable growers might consider high tunnels

High tunnel - Quonset style.jpg

Due to South Dakota’s short growing season, vegetable growers and gardeners have to wait until mid- to late-May to plant warm season vegetable crops to avoid frost injury.

High tunnels may be a way to get an early start says, Geoffrey Njue, SDSU Extension Specialty Crops Field Specialist.

“Although the danger for frost damage is very great in April and May, the day length is increasing and the sun angle is also getting higher. The increasing day length and sunlight provides optimum conditions for plant growth and development,” Njue said. “High tunnels provide growers and gardeners a way to capture the light and heat from the long days for crop growth. They enable growers to start tender and warm season crops in an environment that is easier to protect from frost.”

What is a high tunnel?

By definition, high tunnels are unheated or minimally heated plastic covered structures, which are relatively inexpensive, in which crops are grown in the soil. High tunnels are ventilated by rolling the sides up or down as needed using a roll bar that is operated manually or by an electric motor, as well as end-wall vents. They are covered with a single or double layer of 6-mil greenhouse grade plastic that is left on the structure year-round and lasts 3-4 years.

“The benefits of using double plastic verses single plastic include; increase in average daily temperature, which is important if you grow vegetables in early spring and late fall and also more wind resistance.” Njue said.

Frost protection in the spring and in the fall can be provided by use of propane heaters or oil burners. Because high tunnels trap solar energy in the structure that warms the air and soil in the spring and in the fall, they provide many benefits to growers, including:

High tunnels extend the production season: In years when the season is late high tunnel production is always early, dependable and the yields are greater and of better quality. High tunnels allow the growers to grow an early crop in the spring and also a later crop in the fall; thereby extending their production season.

High tunnels increase crop yield: High tunnels provide optimal growing environment and the crops grow more vigorous than in the field. The potential yield in high tunnels is therefore much higher than in field production – two to four times greater depending on the crop. In high tunnel production the grower can control water, fertility and temperature. With optimal growing environment in the high tunnels, the crops can produce to their full genetic potential.

High tunnels reduce the use of pesticides in crop production: Because of the protected environment provided by the high tunnel, there is reduced occurrence of insect and mite pests. The protected and controlled environment in the high tunnels makes it less ideal for disease organisms. This reduces the occurrence of plants diseases. The reduced occurrence of insect and disease damage means there is less use of pesticides in high tunnels compared to field production.

High tunnels increase profitability for growers: Due to earlier planting, extended production period and better growing environment, the growers who sell their produce are able to provide good quality produce to the market for a longer period of time. By providing good quality produce early and later in the season the grower is able to get premium prices at the market.

Types of high tunnels

The most commonly used high tunnels are the Quonset and the gothic-shaped structures. They are constructed of metal bows which are attached to metal posts driven into the ground. There are various designs of each with different advantages and disadvantages.

Quonset style: The Quonset style high tunnel has been popular for a long time due to its simplicity. However the circular shape of the structure limits the height at the sides which limits the production of tall or trellised crops. The Quonset style is also not very strong and may not be able to support a lot of snow load which may require the plastic to be removed before winter.

Gothic style high tunnel: The gothic style high tunnel has a peaked design which allows for greater height along the sides. This results in increased usable space than the Quonset style.

and is more useful for growing crops including tall or trellised crops.

The gothic style is also structurally stronger and sheds snowfall better than the Quonset style. The peaked roof also allows for better escape of hot air from end wall vents, an important feature since high tunnels can very quickly become overheated, even when outside air temperatures are relatively cool.

To learn more and view photos of the different types of high tunnels, visit iGrow.org/gardens.

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High tunnels may be a way to get an early start to plant warm season vegetable crops to avoid frost injury

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