Construction and Management Considerations Important For High Tunnel Success

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

There have been many high tunnels that have gone up recently on vegetable farms, partly due to available cost share programs.

High tunnels require proper set up and then daily management for crops to perform well in them.

Considerations include:

Site selection: A tunnel site should have good soil, flat but with drainage away from the interior (for rainwater off of the cover), with no shading from trees. Protection from heavy winds can be valuable but ventilation (air cross flow when side curtains are open) should not be significantly impeded.

Soil management: Because it is a small area to be used intensively and is usually set in place and not moved, consideration should be given to improving soils and correcting soil problems prior to erecting the tunnel such as adding compost to increase organic matter and improve soil health.

Cover selection and cover management: Single or multiyear covers, thickness, single or double sheets, tightness, and strapping for minizing wind effects are all considerations. Shade covers for summer production should also be considered.

Side curtain design and operation: This is one of the most critical parts of the high tunnel. Side curtains should be designed for ease of opening and closing and the ability to partially open. They will be opened and closed daily or even several times a day so ease of operation is critical.

End walls and door design and management: If compact tractors are to be used to establish beds than end doors must be designed to allow access. End doors are also a part of the ventilation and should be designed as such for easy opening and closing and partial opening and closing

Ventilation management: Ventilation management is a critical part of high tunnels. Venting is necessary to manage temperatures and allow for removal of excess heat, reduction of humidity in houses, and for wind movement for crops like tomatoes that require wind for pollen movement and fruit set. Side curtains and end walls need to be opened at the correct times and closed prior to temperature drops to accumulate heat for the night. Prevailing winds need to be considered.

Heat accumulation and managing for freezes: This includes decisions on when to keep houses tight and accumulate the maximum heat during the day, when to close curtains, the use of row covers in the tunnel for freeze protection the use of heat sinks to store and release heat, and other heat accumulation and freeze protection techniques. This needs to be tailored to the specific crops being grown

Beds and walkways: Bed formation, bed management, and walkway management should all be set up to maximize root performance, minimize compaction and facilitate maintenance and harvest. Use of permanent beds or box beds, raised beds, flat ground production all are options. One key is to maintain the same walkway areas each year to limit compaction to dedicated areas.

Mulching, ground cover, and weed management: Choice of plastic mulch, landscape fabric, or natural mulches will affect earliness and weed control.

Irrigation choice and management: Drip irrigation, microsprinklers, and hand watering are all options. The key is to take advantage of the ability to control water without the effects of heavy rainfall. This should be tailored for the different crops – drip irrigation for tomatoes, microsprinklers for greens beds, and hand watering for baby greens for example.

Disease management: While most foliar diseases are reduced in high tunnels, there can be a build-up of soilborne diseases if rotations are limited.

Insect and mite management: Tunnels often see an increase in mite problems and different insect profiles than outdoor production.

Crop choice, rotation and seasonality: Almost anything can be grown in a tunnel, including vegetables, cut flowers, small fruits, and even dwarf tree fruits. The key is to match your production and markets with what is most profitable for the limited tunnel area. What will make the most money per square foot per month? Also consider rotations to avoid disease buildup.

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