Like Apples to Oranges... Kind Of
Shane Smith, author of The Greenhouse Gardener’s Companion, defines a greenhouse as a structure that is heated. By his simple definition, a greenhouse allows the grower to control the temperature and environment within a specific range in order to optimize temperatures for peak growth throughout the year.
Sticking with this accepted standard, an easy way to make the distinction between the two structures is that a high tunnel uses passive ventilation for air exchange and cooling. Conversely, a greenhouse is usually equipped with electricity and has automated heating and ventilation systems – more on this below. But keep this in mind when trying to explain the difference to someone else: High tunnel = passive. Greenhouse = active. This is a rudimentary understanding but usually a helpful jump-off point.
The key term here is usually. More and more, these two options are overlapping and evolving with the needs of growers. But for the purpose of this blog, we will go by the traditionally accepting definitions of each of these options.
Both options are used to extend growing seasons. Often, a high tunnel is used for “season extension” while a greenhouse can be used for four-season growing. Both help growers get started earlier in spring and grow longer into the cooler, darker days of autumn.
Because there is no automated heating or ventilation in a high tunnel, they are used mainly in more temperate regions to increase temperature in early spring, fall, and sometimes winter. Again, this depends on your location and also what crops you choose to grow.
But both high tunnels and greenhouses also provide value in more tropical regions by shielding crops from excessive rainfall. Reduced moisture means reduced chances of destructive diseases such as Phytophthora root rot. For anyone that has ever lost a harvest to this destructive disease, introducing a buffer between your plants (and livelihood or food source) and the elements cannot be understated.
How do these structures protect your plants? Each option is also covered in a glazing – or a material used to shield your crops from the various environmental and pest-related antagonists discussed earlier. These will vary between the options and are explained in more detail below.
And while the accepted standard is that high tunnels are the less “plugged in” version of growing structures, both can be equipped with heating and ventilations systems.
Think of a high tunnel as a hybrid of a greenhouse and open field growing option. Your crops are protected from the elements and other destructive forces such as wildlife and harmful insects, but are not in an entirely closed space as with a greenhouse. For the sake of clearly defining what separates a high tunnel from a greenhouse, this section will be a bit more comprehensive than The Similarities.
Just as a high tunnel protects your crops from elements such as dipping nighttime temperatures, excessive exposure to rain, and destructive windloads, a greenhouse will provide the same value but often with a higher level of durability. The added benefit is the ability to take on more punishment from wind and from the weight of snow, and also to keep out the cold even deep into the coldest Alaskan winters.
With the added durability and season-extending capability, comes an uptick in price. There are high tunnels that are more expensive than greenhouses, but it is safe to assume that high tunnels offer a lower cost per square foot than you can expect from a greenhouse. But with the capability to grow year round, it is possible to offset those added costs with an added season of generating revenue.
How Crops Are Planted
With a greenhouse, plants are grown on benches, raised bed kits, or hydroponically. In a high tunnel, crops are often grown directly in the soil or in raised beds.
Ventilation and Heating
While there are overlapping options in terms of heating and ventilation, the accepted standard is that a greenhouse comes equipped with these options and a high tunnel allows for this option in specific cases. And while each will have a glazing that covers the structure, a greenhouse is made of polycarbonate, glass, or double-layer film and a high tunnel is usually covered in a single-layer film. We discuss the various glazing options in a previous post for those that wish to better understand their options.
Ventilation in a high tunnel is typically roll-up sides and large open doors at each end of the tunnel. When these openings are closed, solar heat builds up inside the structure during the daytime and can keep it warm through the night. Of course, this will not serve growers very well in hardiness zones 1-4 where nighttime temperatures plummet well below freezing with little sunlight during the day. A greenhouse is more useful in this scenario as ventilation is usually a collection of fans, ducts, and vents to optimize the environment through an automated environmental control system.
Here at Rimol, we like to think and design for what best serves our customers. That line of thinking is what leads us to create such options as our Catamount Coldframe or Rolling Thunder. This option suits growers that want to find the sweet spot between a more robust greenhouse such as the Matterhorn and Nor’Easter, and a simple coldframe that will not provide the same level of season-extending benefits.
The benefits of both options are many and specific to your region, crops, and purpose. And the more growers that produce fresh, local produce year-round, the more local economic impact these operations will have on their surrounding community. Plus, who doesn’t love fresh, snappy produce or fresh-cut flowers grown by a neighbor just down the road? In fact, the USDA is so adamant on getting more growers to use these structures that the will subsidize the costs to make that happen.
If you’re still not quite sure about how to decide between the two options, or just have questions that were not covered here, get in touch. We’re always here to help you solve the mystery of finding the perfect greenhouse – or high tunnel – for you.