Greenhouses vs High Tunnels vs Cold Frames
Greenhouses vs High Tunnels vs Cold Frames
Greenhouse vs a High Tunnel vs a Cold Frame
Greenhouses, High Tunnels, Cold Frames? What? Aren’t they all the same thing? Nope. Read through to see the differences and the similarities between these structures.
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All of these structures consist of a frame and glazing material. They are all used to grow plants, be they vegetables, ornamentals, fruits, trees, etc.
The structural and architectural features of each of these structures will vary somewhat. The way in which they are used, for example, the temperature maintained in the structures, will vary a lot. The configurations of the buildings will also be somewhat different. Some are considered temporary, some are permanent.
Well, this doesn’t help either. There are 2 different types of structures that are referred to as cold frames. First is this small, low to the ground frame with a cover that is used to protect plants in cooler weather.
The cold frame we are concerned with is as pictured below. It is low to the ground, usually between 14’ to 24’ wide. The lengths will vary. They are typically unheated with natural ventilation from opening the large doors at the ends. They will be in a half hoop configuration and typically covered with a single layer of polyfilm.
The reasoning behind the low height is that it will help to hold the heat in closer to the ground. They offer protection from frost for container trees, shrubs and perennials. They allow you to plant crops 3 – 5 weeks earlier in the spring and fall seasons. Cold frames can also be used to grow cool weather crops.
Many people will remove the polyfilm at the end of the season and use these as a shade structure by placing a shade cloth over the top of the frame. They are typically considered a temporary structure, but you should always check with your building codes department before building any structure.
The high tunnels are much taller at the peak than a cold frame. They can also be much wider structures. They are also typically considered a temporary structure as they have no foundation. They are portable and can usually be added onto easily. Typically, these structures have no foundation or sidewalls. They are simply constructed using hoops or bows driven into the ground.
They are usually glazed with a single film and use natural passive cooling with methods such as roll up side curtains and opening the doors in the end wall. In fact, that is probably the one statement that sums up the difference between a greenhouse and a high tunnel the best.
A greenhouse uses active methods of climate control while a high tunnel uses passive methods. The operating costs of a high tunnel will be much lower than a greenhouse. Some people do install a ventilation system or heating system in their high tunnel. Sometimes it is necessary for the desired growing conditions of the crops planted.
Of course, there are differences in the framing and glazing as well. A high tunnel will typically have a pipe or pvc frame. It is usually covered in a single polyfilm. They usually have large openings at the ends for the entry of equipment such as small tractors.
The NRCS (National Resources Conservation Service, part of the USDA) has an initiative program that helps growers get partial funding for high tunnels. According to their website …
While they may look like greenhouses, high tunnels are actually quite different. Greenhouses are usually constructed of glass and metal, with plants grown in pots above the ground. High tunnels are polyethylene, plastic or fabric covered hoop structures that can be assembled for a fraction of the cost, with plants grown in raised beds or grown directly in the ground.
Advantages of high tunnels are
- The quality of plants and soil and increased
- There is more control of the growing conditions than with outdoor growing
- Extending the growing season
- Cut back on pesticides and unwanted nutrients
- Greater yield
- Minimize energy usage
Greenhouses are considered a permanent structure often requiring a building permit. They will have a proper foundation and be anchored securely to the ground. The foundation should be built according to the local codes in your area. If you are in an area that freezes you will need to build the foundation to the required depth to accommodate the freeze / thaw cycle.
The framing is usually a more permanent material such as aluminum or steel. Glazing can be single or double polyfilm, polycarbonate or glass.
The biggest difference between a greenhouse, cold frame and high tunnel is the systems that are put into place in a greenhouse. There will be ventilation systems, most requiring electricity. These may consist of roof vents or exhaust fans and shutters.
Greenhouses will also have heating systems such as a natural gas, propane or electric heaters.
Additional equipment you may find in a greenhouse would be lighting, evaporative cooling, timers and controllers, and advanced equipment to monitor parameters for the professional grower.
Greenhouses may be used year-round due to these systems that control the climate inside.
Typically, plants in a greenhouse are not grown in the ground, but in containers on benches, using hydroponic systems, or in raised beds.
We find that even though they look alike at first glance, there are considerable differences in the purposes of these three structures. While they are all used for growing, they are all used for growing different end products in different ways. But, they are all useful in their given purpose.
Just make sure that you do not buy a cold frame or high tunnel and expect it to function like a greenhouse. And remember in order for a greenhouse to function properly you must have the systems in place to get your climate where you need it to be.
Regardless of what crops and how you want to grow them go get a cold frame, greenhouse or high tunnel today and extend your growing season. Enjoy!