Hoop houses, often called high tunnels, are simple, tunnel-shaped structures used in agriculture to create a controlled environment for crops. They function as passive solar shelters, capturing and retaining the sun’s heat to modify local growing conditions. They are a cost-effective way for farmers and gardeners to gain an advantage over the unpredictable nature of outdoor growing. The primary purpose is to extend the typical growing season, allowing for earlier planting and later harvesting.
Structure and Materials
The physical design of a hoop house is defined by its arched frame, which is built from a series of parallel hoops or “bows” that create the tunnel shape. These bows are commonly constructed from galvanized metal tubing, which offers strength and resistance to rust, but they can also be made from materials like PVC piping or wood for smaller, less permanent structures. The simplicity of this frame allows for relatively easy assembly and disassembly compared to more complex structures.
The entire frame is covered with a single layer of UV-stabilized polyethylene plastic film, which acts as the transparent barrier. This specialized film is designed to withstand solar degradation while allowing sunlight to pass through efficiently. The covering is typically secured along the base and end walls, often using a system of metal channels and “wiggle wire” that holds the plastic taut against the frame.
Hoop houses are generally considered semi-permanent structures because they typically lack a substantial, permanent foundation. Instead, the frame is anchored to the ground using methods such as metal ground posts driven into the soil or wooden baseboards secured to the ground. This anchoring system means the structure can sometimes be moved to a different location.
How Hoop Houses Affect the Growing Environment
The functional core of a hoop house lies in its ability to harness passive solar heating through the greenhouse effect. The transparent polyethylene film allows short-wave solar radiation to enter and warm the air, soil, and plants inside. Once absorbed, this energy is re-radiated as long-wave infrared heat, which the plastic film traps, effectively insulating the interior and raising the ambient temperature.
This retained heat enables season extension, allowing growers to start delicate transplants weeks before the last expected frost and continue harvesting cold-tolerant crops well past the first hard freeze. The structure also provides a significant layer of protection against harsh weather elements. Crops inside are shielded from damaging wind, heavy rain, hail, and excessive snow loads.
Managing the internal microclimate requires active human intervention, especially concerning heat and humidity. On warm, sunny days, temperatures inside a closed hoop house can quickly rise to levels detrimental to plant health. To prevent overheating and facilitate air exchange, growers use passive ventilation methods, such as rolling up the sides of the plastic film or opening large doors on the end walls. This manual control releases excess heat and moisture, regulating the temperature and humidity for optimal plant growth.
Comparing Hoop Houses to Greenhouses
Hoop houses and greenhouses both create controlled growing environments, but they differ fundamentally in their approach to climate control and permanence. The most significant distinction is the heating source, as hoop houses rely almost entirely on passive solar gain. Greenhouses, by contrast, are often equipped with automated systems, including active heaters, cooling fans, and mechanical ventilation, providing a much higher degree of precise climate management.
Greenhouses are typically built as permanent structures, often featuring concrete foundations and rigid coverings like glass or polycarbonate sheeting. Hoop houses, being semi-permanent and anchored less substantially, are generally simpler and quicker to construct. Their lower complexity translates to a lower cost for both initial setup and ongoing operation, as they do not require utility hookups for active heating and cooling systems.
The difference in complexity and permanence affects legal requirements. Because they are temporary or semi-permanent and lack active climate control, hoop houses often face fewer or less stringent permitting regulations than a fully equipped greenhouse structure. Ultimately, a hoop house is primarily a tool for extending the natural growing season, while a greenhouse is designed for year-round production of a wider variety of crops regardless of the external climate.