Greenhouses vs High Tunnels vs Cold Frames

Greenhouses vs High Tunnels vs Cold Frames

Greenhouses vs Cold Frames vs High Tunnels

Differences between greenhouses, cold frames and high tunnels

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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Similarities

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.

Differences

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.

Cold Frames

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.

Cold Frame

Cold Frame

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.

High Tunnels

High Tunnel

High Tunnel

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

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.

Conclusion

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!

 

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Learn About Greenhouses

hobby greenhouse association

hobby greenhouse association

Have you always dreamed of owning a greenhouse? But you are overwhelmed with all the decisions to be made and learning how to properly grow in one? Maybe you already own a greenhouse and just have a few questions you would love to ask someone with experience.

There is a solution. Become a member of the Hobby Greenhouse Association.

A lot of people think that you buy a greenhouse, set it up in the backyard, and voila you have beautiful plants growing with no problems. Not so. I am not suggesting that this is a torturous process but growing in a greenhouse is a learning curve. And it is a different process for all of us. Just consider all the different types of plants we are growing, not to mention our differing climates and plant needs.

A lot of people make the mistake of loading up their new greenhouses with every piece of equipment that they can find. Others go the opposite way and think that the greenhouse is the only piece of equipment they will need.

I suggest that when purchasing a greenhouse, you consider the ventilation needs, whether you will be having electricity or will be cooling your greenhouse without electricity. If it is the middle of winter, I suggest thinking about how you will heat your greenhouse. Will you use a gas heater, or heat it by taking it off the grid? Other accessories can be added as the need arises.

This is where the HGA comes in. The members who already have greenhouses are more than willing to share their experiences and knowledge on these types of concerns. They have been there and done that. But, don’t take that to mean you have to already own a greenhouse to join. All interested parties are welcome.

What will the HGA do for me?

Lots. You can go to the website and review the current newsletter. Or, you can even opt for receiving this by regular mail if you prefer. You can join discussions in the members blog area by asking a question or sharing a bit of knowledge that you think other greenhouse growers would find helpful. You can also submit a question by email to other members. Flowers as well as vegetables are discussed.

Current topics on the blog include pictures of a mystery plant that someone is trying to identify. Also, someone in Massachusetts is looking to connect with other greenhouse enthusiasts. There is a lively discussion about starting new plants. Also, a question with lots of comments is “How are your plants surviving the winter?” Of course, this question was asked last winter.

One of the neatest benefits of the organization is the round robins. The robins are focused on a greenhouse gardening topic including management (of the interior environment), vegetables and others. They consist of a packet of letters from each robin member. When one arrives, always by snail mail, the recipient writes a few paragraphs about how their greenhouse has done with the robin subject since receiving the last packet, typically a few months previously. Then he/she adds paragraphs addressed to each in the group, answering questions and/or commenting of what that person wrote in the last round. Then adds this letter to the packet, removing their last letter, and mails it to the next person on the list of about eight members. Then the person e-mails the coordinator with when the packet was received and when sent on. The description of the robins is from Tom Karasek, the President of the Hobby Greenhouse Association.

Discounts for Members

There is also a group of hobby greenhouse businesses that offer a discount to HGA members. All you need to do is find them on the list and ask for your discount. Advance Greenhouses has offered this discount for years.

How did this organization get started

In 1975 a gentleman named Wander Mall got a brand new hobby greenhouse. If you remember this was way before the internet and the information overload era. He found that there was just not that much information available on how to use the greenhouse. He decided that a club with a few like minded growers would be the answer. It would be a free exchange of information with people learning from others mistakes. He sent some letters to the editors and had a more than acceptable response. There was also a radio and TV show hosted by (Doc) George and Katy Abraham that promoted the newly founded organization. Membership quickly increased to over 1000 members. It seems like a lot of people had similar questions. And, I have got to tell you from my personal experience that there is not a group that is more willing to share their knowledge than gardeners. Of course, there are a lot of us with strong personal opinions of how things need to be done. We just can’t help ourselves.

The HGA today

The HGA continues to prosper today due to the many volunteers who have contributed their time and effort through the years. Of course, there is not enough room to personally list and thank each of them. But they know who they are.
If you are interested in hobby greenhouse growing, you will enjoy the camaraderie among this group. I suggest that you check it out today and join. Get your questions out there and get help from people who truly enjoy growing in a greenhouse. And, get your own greenhouse up and growing. There is nothing more satisfying.

Conclusion

In full disclosure I will tell you that I am currently the Vice President of this organization. And, we have participated in their member discount program for over 15 years. Tammy

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Taking Your Greenhouse Off The Grid

Taking Your Greenhouse Off The Grid

Taking Your Greenhouse off the Grid

Taking Your Greenhouse off the Grid

Want to save money on heating and cooling your greenhouse? Want to become more self sufficient? It is quite possible to take your greenhouse off the grid. But first you should determine if this is what you need. Sometimes you do not need to heat the winter greenhouse, although you will probably need some ventilation.

How Does A Greenhouse Work?

Greenhouses are covered with glass or translucent materials to let the sun’s rays enter the structure. That is why you will notice that the R value (insulation factor) for a greenhouse is much lower than a wall for your house.

The rays enter the greenhouse and hit a solid surface such as the ground, a pot, leaves etc and they are turned into heat. The shorter wavelength infrared rays that entered will become longer wavelength energy that is absorbed. The greenhouse will stay warm during the day as the light is entering and being transformed into energy faster than the heat can get out.

At night you will lose heat to the outside by radiation cooling. This is because the objects in the greenhouse are much warmer than outside. They will lose heat by emitting infrared radiation through the glazing. But, there are several solar methods you can apply to assist heat retention.



Water

I just read about a huge greenhouse operation that put in ponds and a recirculating system to water their plants. They are using 100% rainwater irrigation. This was at a cost though of 1 Million Dollars. This is not practical for the small grower or backyard hobby greenhouse. And I believe the system required electricity.  Although there are several things we can do.

I have talked to people who use ponds and recirculate their water on a smaller scale than the operation mentioned above. But, probably one of the simplest things to do is use rain barrels or cisterns to catch the rain water. If you are going to do this be aware of your local codes. This is illegal in Colorado. I am not aware of any other States at this time, but just check and be sure.

Solar methods of taking your greenhouse off the grid

Of course you can try to “trap” as much heat during the day as possible to be emitted into the greenhouse at night. One way to do this is to place dark containers full of water in the greenhouse. I used to have black 55 gallon drums under my benches filled with water. This will hold the heat that is built up during the day. It will then release it at night to warm the greenhouse.

You can place a solar blanket on the outside of the greenhouse at night.  A good heavy blanket will help hold in any escaping heat.

You can ” double up” your glazing by placing smaller cold frames inside your greenhouse. This will give you extra insulation.

Heating the Greenhouse

Once you have determined that your crops need additional heat, you will need to supply a heat source.

A compost pile is a good source of heat. The piles will heat up to 150 degrees F. You will have to set up a heat exchange system with tubes filled with water. Some will keep the compost pile inside their greenhouse. Others will leave the pile outside, to conserve valuable space,  and run their tubing through the greenhouse.

Manure can be put in crates and placed inside the greenhouse. You can place plants on the tops of these crates for additional heat.

You can use a wood burning stove, such as a rocket heater. These have a large thermal mass that will hold the heat for a long time even after the fire is out. These are very efficient for heating.

Geothermal heating and cooling can be done in some climates. This utilizes the temperatures in the ground to control your greenhouse. In the winter it takes the heat from the earth. In the summer the ground acts as a heat sink.

Cooling the Greenhouse

The greenhouse will build heat much earlier in the season than some people think. I tell people who are only overwintering plants that they too will need some type of ventilation.

The simplest way to vent air is to use roof and side vents. The roof vents allow the hot air which rises to leave that way. When you use side vents in conjunction with them you get a chimney type affect.

These are simple to control with the solar powered roof vents that are readily available. These have a wax cylinder in them and work on contraction and expansion.  When the wax gets warm it expands and pushes the vent open. When the wax cools it contracts and pulls the vent shut.



A shade cloth is a simple way to cool the greenhouse a few degrees. If you think about this it is pretty much the same as standing under a shade tree in the summer.

Roll up side curtains can be placed on any greenhouse with straight sides. These can be motorized, but they are also available with hand cranks. These open up the greenhouse considerably for a fresh air flow.

Solar powered ventilation systems are now available. These include an exhaust fan, intake shutter(s) and a thermostat. They operate the same as electrically powered ventilation systems, but they are powered by solar panels.

If you have water available you can add a misting system on a battery operated timer. These will help cool the inside through evaporation.

 

Conclusion

A greenhouse is a wonderful addition to your backyard, homestead or farm. But, you must have them set up correctly for your climate and  your crops. Even if you are unable to take it completely off the grid, try a couple of these methods to save on your power bills.

Let us know in the comments which of these methods you have tried and how they worked for you. Also, if you have any additional methods you have used that worked, please feel free to share those with us.




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