Whether you’re new into agriculture or just want to grow lots of crops out of season, you might wonder what structure to get between a high tunnel and a greenhouse.
High tunnels are large, tall structures primarily used for season extension and agricultural purposes. Similar to hoop houses, high tunnels are made of metal or plastic arches covered with plastic sheeting. They are inexpensive, but provide limited climate control.
Greenhouses are more permanent – and more expensive – structures used for year-round growing. They have a metal or wood frame fitted with glass, acrylic, or polycarbonate panels. The structure is more resistant and provides better climate control. However, it is more difficult to move if needed.
The table below shows a quick overview of the differences between high tunnels and greenhouses:
| Characteristics | High Tunnel | Greenhouse |
|---|---|---|
| Purpose | Season extension | Year-round growing |
| Site preparation | No preparation | Compacted soil, paving slabs, or concrete foundation |
| Construction | Mobile | Semi-permanent or permanent |
| Ventilation | Manual | Manual or automatic |
| Heating | No | Yes |
| Light transmission | Higher | Lower |
| Pest control | Higher | Lower |
| Uses | Large-scale gardening | Multiple uses |
| Cost | Higher | Lower |
9 Differences Between High Tunnels and Greenhouses
Evaluating your needs is the first step to finding the best cold season growing structure for you. Do you have a very large garden or an agricultural field? Or do you need something to grow crops and winter your perennials? Once you’ve answered these questions, the differences below might help you decide.
1. Purpose
High tunnels and greenhouses are both used for cold-season growing, but they have different purposes.
High tunnels are primarily used to extend the growing season, protect plants from adverse weather, and increase the overall crop yield.
They do this by providing a protected environment in which gardeners can start planting earlier in the spring and continue growing later into the fall, or even throughout the winter, depending on the crop and climate.
The controlled environment inside a high tunnel allows for better management of soil moisture and temperature, fostering more robust plant growth.
A greenhouse is a more advanced and versatile structure that provides a controlled environment for growing a wide variety of plants. With their advanced climate control systems, greenhouses allow for year-round growing of various crops, regardless of the outdoor climate.
Due to their versatility, greenhouses can accommodate different growing techniques, such as hydroponics, aeroponics, or container gardening. Greenhouses can also be used for plant research and propagation, where a controlled environment is essential for successful experiments and plant development.
2. Site Preparation
Proper site preparation is crucial for ensuring the long-term success and functionality of your growing structure.
High tunnels, even the largest ones, are temporary structures that need little to no site preparation. The structure is supported by poles that are driven into the ground, but you don’t need a foundation or any type of solid support.
Because poles can be driven into the ground at different depths, high tunnels can be installed on uneven soils. All you have to do is to remove any vegetation, rocks, or debris from the selected site, to make sowing easier.
Greenhouses are semi-permanent or permanent structures typically built on a foundation. Alternatively, compacted soil or paving slabs are required. This is necessary so that you can anchor the fixing plugs or bolts.
Due to the rigid structure of the greenhouse, the terrain must be as level as possible. You might also want to pick a location with plenty of sunlight, good drainage, and nearby utilities.
3. Construction
While both structures share a common goal of creating a controlled environment for plant growth, they differ significantly in their design, materials, and complexity.
High tunnels are typically constructed with galvanized steel frames or PVC pipes, which are bent into a series of hoops or arches, creating a tunnel-like structure. The frame is supported by purlins (horizontal supports) and, in some cases, cross braces for added stability.
The frame is covered with polyethylene or other plastic materials, which provides protection from the elements, retains heat, and allows light to penetrate. The same material can be used to cover the ends of the tunnel, or you can use polycarbonate, metal, or plywood panels.
Regardless of the actual materials, high tunnels are relatively easy to erect.
Greenhouse frames are generally more rigid and can be constructed from various materials, such as aluminum, steel, or wood. The frame is designed to support the weight of the covering material and withstand weather conditions.
These structures can be covered with glass, polycarbonate, or high-quality plastic panels, each offering varying levels of light transmission, insulation, and durability.
The walls are also more solidly constructed, often using the same materials as the frame and covering. They typically include doors, windows, and vents for access, ventilation, and temperature control.
Moreover, greenhouses are generally equipped with more advanced climate control systems and require a foundation. Constructing a permanent greenhouse typically requires permits and compliance with your local building codes.
This is why building a greenhouse is much more laborious and expensive than constructing a high tunnel.
4. Ventilation
Ventilation is a critical aspect of maintaining a healthy growing environment, as it helps regulate temperature, humidity, and airflow. Both high tunnels and greenhouses have distinct ventilation methods, which play a significant role in their overall functionality.
High tunnels primarily rely on passive ventilation, which uses natural airflow and temperature differences to circulate air within the structure.
The most common method of ventilation in high tunnels involves roll-up or drop-down sides, which can be manually or mechanically adjusted. They may also feature vents in the end walls, or ventilation can be achieved by leaving the ends of the tunnel open completely.
Greenhouses often feature more advanced and active ventilation systems that can include a combination of exhaust fans, intake vents, and circulation fans.
Like residential buildings, greenhouses typically have roof vents, which can be opened or closed to release hot air and draw in cooler air from outside. These vents can be manually operated or automated with temperature-sensitive controls.
Some greenhouses may also include side vents or louvers to further regulate air circulation and temperature. Exhaust fans and intake vents, as well as circulation fans, are also used in larger, more advanced greenhouses.
5. Heating
Heating is also crucial for maintaining optimal growing conditions, especially in colder climates or during the winter months.
High tunnels primarily rely on passive solar heating, where the sun’s energy is absorbed and trapped within the structure during the day. The plastic covering helps to retain heat, providing a warmer environment for plant growth.
You can enhance passive heating in high tunnels by incorporating thermal mass elements, such as water barrels or rock-filled containers, which absorb heat during the day and release it slowly during the night.
In colder temperatures, row covers or frost blankets provide additional insulation and protection for plants within the high tunnel.
Although less common in high tunnels, supplemental heating systems, such as propane or electric heaters, can be used if necessary. Keep in mind that the energy efficiency of high tunnels is reduced when using supplemental heating, and proper ventilation must be ensured to avoid excessive humidity and potential plant damage.
Similar to ventilation, greenhouses typically employ active heating systems, such as natural gas, propane, or electric heaters, to maintain consistent temperatures throughout the structure.
Some greenhouses use radiant heating systems, like hot water or steam pipes, which distribute heat evenly across the greenhouse floor or growing benches. Forced-air systems, such as unit heaters or furnaces, can also be used in greenhouses to circulate warm air throughout the structure.
Infrared heaters are another option for greenhouses, providing targeted heating by emitting radiant heat directly to the plants and the soil.
Greenhouse heating systems can be integrated with other climate control elements, such as ventilation, cooling, and humidity control, allowing for precise and automated management of the growing environment.
6. Light Transmission
Another essential factor in plant growth is light transmission, as it affects photosynthesis, flowering, and overall plant health. Both high tunnels and greenhouses are designed to optimize light transmission, but the materials and construction methods used can influence the quantity and quality of light available to plants.
High tunnels are typically covered with a single or double layer of polyethylene or other plastic films. These materials allow for a high level of light transmission, usually around 80 to 90%, depending on the thickness and type of plastic used.
The bright side is that the plastic covering in high tunnels diffuses light, scattering it more evenly throughout the structure. This helps reduce shadows and promotes more uniform growth in plants.
However, over time, the plastic covering can become cloudy or discolored due to UV exposure, which can reduce light transmission. It is essential to replace the covering material as needed to maintain optimal light levels.
Greenhouses can be covered with various materials, such as glass, polycarbonate, or high-quality plastic panels. Each material offers different levels of light transmission, with glass typically providing the highest level (up to 90% or more), while polycarbonate and plastic may vary between 80 and 90%.
Another aspect that can affect light transmission is glazing. Greenhouses with glass or polycarbonate coverings can utilize different glazing options, such as single, double, or triple-pane configurations. Double or triple-pane glazing can improve insulation but may slightly reduce light transmission compared to single-pane glazing.
While light transmission is usually higher in a greenhouse, light diffusion is lower compared to high tunnels. This translates into a higher risk of hot spots within the growing environment. For this reason, plants in a greenhouse should be arranged considering the sunlight and shade exposure.
7. Pest Control
High tunnels and greenhouses are structures developed to protect plants from frost rather than pests. However, they can also keep bugs and wildlife away from your crops, with varying degrees of success.
Greenhouses have the upper hand, especially if built on slabs or a concrete foundation. The rigid panels and sturdy structure are difficult to pass through, especially if the greenhouse features an integrated climate control and ventilation system.
High tunnels may keep some pests out, but the plants grow directly on the ground. The plastic film provides some sort of barrier, but bugs might seep through. Wildlife can also get inside, either by damaging the film or by sneaking into the tunnel from underneath the plastic film.
Hence, greenhouses provide a higher degree of pest control management.
8. Applications
Both greenhouses and high tunnels are designed to create controlled environments for plant growth, but their construction and climate control capabilities lead to various applications suited for each.
High tunnels are commonly used to extend the growing season by providing protection from frost and cold temperatures in early spring and late fall, allowing growers to start planting earlier and harvest later than they would in an open field.
These structures are also used for growing specialty or high-value crops, such as heirloom tomatoes, berries, and cut flowers, which may benefit from the controlled environment and protection offered.
Greenhouses are designed for year-round growing, with advanced heating, cooling, and ventilation systems that provide precise climate control, allowing growers to produce crops consistently throughout the year.
They are often used for starting seeds, propagating plants, and nurturing young seedlings or transplants before they are moved to the field or sold to customers. Greenhouses also provide ideal environments for research institutions, universities, or schools to study plant growth, test new varieties, or teach horticulture principles.
Compared to high tunnels, greenhouses can support a wide range of crop production, from vegetables and fruits to ornamental plants, flowers, and even some tree species, thanks to their ability to maintain optimal growing conditions regardless of the outdoor climate.
9. Cost
Lastly, it’s important to consider the initial investment, ongoing maintenance, and energy expenses when comparing these two structures.
High tunnels are cheap to erect, with costs varying between $2.5 and $5 per square foot. Maintenance is minimal and cheap; the only thing you have to worry about is the plastic sheeting. Moreover, high tunnels are typically not connected to utilities, so you won’t have to bother about energy bills.
Greenhouses can cost between $10 and $25 per square foot, depending on size and type. The rigid panels are more expensive to replace than plastic sheeting, and you’ll also have to worry about energy efficiency and utility bills, if you use them in your structure.
Conclusion
High tunnels and greenhouses serve similar purposes, but you may have to choose one over the other depending on your needs.
If you only want to extend the growth season without breaking the bank, a high tunnel is for you. This structure provides some protection against pests and elements, and is also ideal for protecting sensitive plants from direct sunlight.
A greenhouse is your best bet if you want to grow crops year-round. This structure provides superior climate and pest control, and you can create areas of sunlight and shade to grow various types of plants at the same time.
However, a greenhouse is more expensive to build and often permanent, so you won’t be able to move it.