High Tunnel Research: Types of High Tunnels
- [Instructor] Welcome to Penn State's High Tunnel Research Facility.
Today, we will cover what a high tunnel is and the types of high tunnels that are available to growers.
A high tunnel is a low-cost, non-permanent structure used to protect plants and extend the growing season.
High tunnels are different from greenhouses in that a high tunnel has no permanent flooring, so the option of planting directly in the soil is maintained, as is the option of moving the structure to a new location.
The structure is usually less complex than a greenhouse and may or may not have electricity.
The frame of the tunnel is covered with one or two layers of plastic for all or part of the year.
The majority of ventilation within the tunnel occurs from natural airflow through the sides or ends of the structure, depending on the type of high tunnel.
When looking for high tunnel providers, be aware that the terminology may not always be consistent.
High tunnels may also be referred to as hoophouses, coldframes, and unheated greenhouses.
In addition, if construction costs are defrayed as part of a subsidized program, certain restrictions may be placed on location, growing methods, and crops grown for a period of time.
The tunnels provide an environment where the plants are protected from wind and rain while still receiving adequate sunlight.
High value, quickly maturing, and long harvest season crops such as tomatoes, cucumbers, salad greens, and berries are commonly grown in the tunnels.
While tunnels are generally used for vegetable or fruit production, other crops such as cut flowers may be grown.
The tunnels encourage increased, earlier, and later production due to the extended growing season and higher temperatures provided by the tunnel.
This can allow growers to cultivate crops that they could not normally grow in their region.
Highly perishable crops such as berries benefit from the extended shelf life resulting from the protected environment.
Now let's look at single bay tunnels versus multi bay tunnels.
Single bay tunnels are freestanding low footprint structures that typically range from 14 feet to 30 feet in width and from 36 feet to 200 feet in length.
There are two roof shapes available in single bay tunnels: gothic or peaked and round or hooped.
The round shape can also be referred to as a Quonset shape.
The peaked roof on gothic tunnels encourages snow to be shed more easily, while round tunnels are more likely to retain snow.
Single bay tunnels with a peaked roof are designed to handle snow loads and can be used to extend the growing capabilities through all four seasons.
In more northern locations, a double layer of plastic with air inflation between the layers may be used.
Single bay tunnels are primarily ventilated using roll-up side walls.
If electricity is available, automated side walls, gable, or roof vents and fans can also be installed.
Since single bay tunnels with a round roof are less likely to shed snow, some producers of these tunnels recommend removal of the plastic for the winter.
Multi bay tunnels, also referred to as poly tunnels or three season tunnels, consist of individual bays that are joined to the sides to provide structural stability.
The bays have rounded roofs and may have a gutter between them to channel rainwater.
The size of the multi bay high tunnel system depends on the number of bays used.
Typically, the width of a bay is 18 feet to 30 feet, and the length can vary widely.
Multi bay tunnels are primarily ventilated by bunching the plastic upwards, and they may or may not have end walls.
Multi bay tunnels are used when the primary goal is to protect the crops from the elements during the normal growing season.
They are not designed to handle snow load, so plastic is removed and bundled during the winter months in areas that receive snow.
Crop production may also be suspended during the warmest months in hotter areas of the country.
Multi bay tunnels can be vented by pushing the plastic roof towards the peak.
However, constraints on time, labor, and tunnel design may limit the height that can be reached.
The rope rigging is attached over the roof at the gutter zones to prevent the plastic from moving due to wind.
When either single bay or multi bay tunnels are not going to be used for an extended period, the plastic covering should be removed to minimize stresses from wind and wear.
The exposed frame typically can tolerate direct exposure to the elements.
When considering a high tunnel purchase, make sure you select the tunnel type best suited for your location, growing needs, and budget.
Frequently Asked Questions