A high tunnel, often called a hoop house, is a simple, protective structure used in agriculture to create a modified microclimate. These temporary or semi-permanent installations shelter plants from environmental extremes, allowing farmers to grow crops outside of the typical outdoor growing season. The high tunnel functions as a passive solar collector, trapping the sun’s heat to warm the air and soil within. This accelerates plant growth and allows for an extended harvest period. This low-cost approach has become a popular tool for commercial growers and homesteaders alike.
Defining Characteristics and Structure
The physical design of a high tunnel focuses on functionality and ease of construction. The structure consists of a framework made of metal hoops or arches, often constructed from galvanized steel tubing, driven directly into the soil. This lack of a permanent concrete foundation allows the structure to be considered temporary or movable, which often simplifies permitting requirements. The frame is covered with a single or double layer of durable, UV-stabilized polyethylene plastic film, which acts as the heat-trapping skin of the tunnel.
A defining feature is the absence of an active heating system, meaning the structure relies entirely on solar energy for warmth. Temperature control and air circulation are managed through passive ventilation, primarily using roll-up sides or removable end walls that can be manually adjusted. This manual process is performed by the grower to prevent the interior from overheating, as temperatures can easily exceed outside ambient temperatures if not vented properly. The crops themselves are usually planted directly into the native soil within the structure, distinguishing them from traditional container-based systems.
Distinguishing High Tunnels from Greenhouses
High tunnels and greenhouses differ significantly in their level of environmental control and permanence. The most substantial difference lies in heating; high tunnels are unheated and rely on passive solar gain for season extension. Greenhouses, by contrast, are often equipped with active heating systems to maintain precise temperatures year-round, designed for climate-controlled production.
Structural permanence also separates the two. High tunnels are semi-permanent and lack a poured concrete foundation, often anchored only by ground posts. Greenhouses are typically permanent structures with a solid foundation, making them less portable. Ventilation is another differentiator; high tunnels use manual, passive systems like roll-up sides, while greenhouses commonly feature automated, mechanical systems and use more rigid glazing materials like glass or polycarbonate panels.
Primary Benefits and Agricultural Applications
The primary appeal of high tunnels is their ability to significantly extend the growing season, allowing for earlier planting in the spring and later harvesting into the fall or even winter. The trapped heat elevates the soil temperature, giving plants a head start of several weeks. A single-layer high tunnel can effectively shift a grower’s climate zone, enabling the cultivation of crops that might not otherwise thrive in that region.
The structure provides a physical shield, offering protection from damaging weather events like heavy rain, hail, and strong winds. This protection results in a higher yield of top-grade produce, as the crops are less susceptible to blemishes and physical damage. Furthermore, the covering prevents direct rainfall from reaching the plants, which allows growers to use precise drip irrigation systems. This improves water efficiency and reduces the incidence of fungal diseases that thrive on wet foliage.
High tunnels are well-suited for high-value crops that benefit from a longer growing window and protection. Warm-season crops like tomatoes, peppers, and eggplants are commonly grown, yielding a higher percentage of marketable fruit. Leafy greens (spinach, kale, lettuce) thrive in cooler seasons and can be grown throughout the winter, while small fruits like strawberries and brambles also benefit from protection.