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To average man-on-the-street, a high tunnel and a greenhouse might look very similar. They both have plants, they both go in your backyard, and they are both a good place to work up a sweat because they are just so dang hot. But those superficial qualities hide a world of differences.
First, you should probably know exactly what each product does.
Greenhouses are sealed, insulated, and transparent rooms that use light to heat themselves up, and a controlled environment to stimulate the growth of plants. High tunnels are open-faced covers for gardens and crops that keep plants healthy and protected.
They are very similar, with both focusing on keeping plants alive and healthy. But while a greenhouse does this by making an artificial environment for them, a high tunnel will preserve the natural environment of the plant. The ramifications of this one difference goes deeper than you might think.
So, for the new and inexperienced grower, what are the key differences between a greenhouse and a high tunnel? What jobs are exclusive to each one? And what do you need to know about them before you buy into either?
- Difference Between a Greenhouse and High Tunnel
- Difference #1: How They Plant
- Difference #2: How They Relate to the Environment
- Difference #3: How They Relate to the Atmosphere
- Difference #4: What is Planted in Each
- Difference #5: What They are Made Of
- Difference #6: Technological Features
- Similarity #1: They Both Work
Difference Between a Greenhouse and High Tunnel
Other than the obvious look, what is the difference between a greenhouse and a high tunnel, do they both do the same thing? why would you even use a high tunnel when a greenhouse works perfectly?
These are some of the questions I will answer but first, let’s take a quick overview of the differences.
Difference #1: How They Plant
The first and most important difference between a greenhouse and a high tunnel is how the plants they grow are actually planted.
Want to know what to plant in a greenhouse for winter then check that article out.
In a greenhouse, plants are planted in pots, troughs, and baskets. Essentially, any container that can hold them and keep water in. They are kept in their own little environments in elevated, artificial ground by these receptacles where their nutrition and water intake can be carefully controlled.
Contrast high tunnels, where plants are planted directly into the ground. This makes high tunnels more similar to traditional gardens, where all your plants are sharing the same, naturally occurring soil.
But what is the meaning of this difference? Well, it affects more than you might think.
When you plant in the ground rather than in a pot your plant’s roots have far, far more room to grow. This means the plant will be better anchored into the ground, which in turn will make it more resistant to high winds and other adverse weather effects.
Plants planted in the ground rather than pots will compete with each other if planted too close together. This can be observed in nature, where trees growing within close proximity will entangle their roots and drain each other’s resources.
Luckily, this only happens in resource-scarce environments. It can also only happen if the plants are planted clearly, visibly too close together. High tunnels solve this problem with another feature afforded by their plants being planted in the ground: With more room to grow downwards, competition is less necessary among the plants.
If you plant too many plants in a pot, they will almost certainly compete no matter how much you feed them. But plant the same group of plants in the ground and they can distance themselves from one another, or even draw sustenance from other sources, like rainwater.
This also means that a high tunnel can only be built wherever the plants you want to grow can be grown. High tunnels can be exceptionally big due to their low cost, but they should only be as big as the land you have access to grow on.
Greenhouses, meanwhile, can be built anywhere. The biggest restriction to where a greenhouse can be built is whether or not it gets shade on the southwest side.
This “southwest side rule” is due to the way the sun travels across the sky: In the summer, when the days are longest, most of the heat a greenhouse gets comes from when the sun is low in the sky late in the day. In other words: When it is in the southwest portion of the sky.
That leads to the next big difference between greenhouses and high tunnels:
Difference #2: How They Relate to the Environment
When it rains, water goes into the ground (as you may have observed yourself). You might expect that your plants can only drink water that lands nearby them, but that is not necessarily the case.
The roots of plants do not take in water with perfect passivity. Rather, they apply minute amounts of suction that draws water in towards them. This is important for plants kept in a high tunnel, as it means that when it rains, they can pull water from outside the high tunnel to their roots to drink.
Of course, this also means there is a slight risk in a high tunnel for the same reason. It is unlikely, so do not let this possibly be the key reason you do or do not buy a high tunnel. But it is physically possible for contaminants in the soil to poison plants even if the high tunnel’s soil is perfectly healthy.
Consider the soil of Flynt, Michigan, or Chernobyl. Even if you plant in a relatively clean patch of soil in these places, the proximity of unclean soil means that your plants will slowly and surely begin to draw nutrients from the unclean places.
Greenhouses do not have this problem. The soil plants use in greenhouses is kept in isolation from the world outside. You could operate a greenhouse in the Sahara Desert, and it would still yield plant growth so long as you managed the Sahara Desert’s malignant heat.
Do greenhouses need a vent is a question I get asked a lot – check out that article here!
The problem greenhouses have instead is that if you do not manage their malignant heat, their soil will dry out. When a high tunnel’s soil dries out from the heat the plants living in it can still pull moisture and nutrients from the ground. When a greenhouse dries out, the plants are doomed unless fed quickly.
This has always been one of the great obstacles of greenhouses, and it is why greenhouses have advanced so much technologically in recent years. Greenhouses can now be equipped with vents, misters, and sensors to automatically manage them, all to allow plants to survive over-hot conditions.
Difference #3: How They Relate to the Atmosphere
During the day, plants consume carbon dioxide and produce oxygen as a byproduct of this consumption. During the night, this process reverses: They produce carbon dioxide and consume oxygen.
Greenhouses take advantage of this by sealing themselves up so no air can leave the cycle. High tunnels are not sealed. This leaves the plants in a high tunnel more susceptible to the quality of the air outside.
Now, it should be noted that greenhouses are only sealed up this way to accelerate growth, not trigger it. No plant requires itself to be sealed in with its own breathing cycle to grow.
For this reason, you do not have to worry about the quality of life for your plants if you choose to plant in a high tunnel. The only time the quality of the outside air will threaten your plants is if the quality of the outside air is so poor that it would threaten you as well.
Difference #4: What is Planted in Each
This might be the biggest difference that decides whether you go with a greenhouse or a high tunnel. It might also be completely inconsequential. It all really depends on whether or not you are interested in becoming a farmer.
Greenhouses can grow flowers, fruits, and vegetables. It takes thousands of dollars of investments, but it is possible for greenhouses to harbor plant life such as corn, watermelons, and apple trees.
Doing that, however, is exactly the headache you are probably imagining it being. Farming is far, far easier in a high tunnel than a greenhouse. This is because greenhouses are artificial environments and creating the environment that suits the needs of corn or watermelon is an extremely costly prospect.
High tunnels, meanwhile, only need to be built over these environments as they already exist. Many crops are easier to grow in a high tunnel than in a greenhouse, and for some crops (such as the aforementioned corn and watermelon) growing in a greenhouse is only technically possible.
But this difference is only really material to you if you plan to farm these hard-to-grow crops from the outset. If you are an amateur grower looking to decide between a greenhouse and a high tunnel, making your decision based off of a high tunnel’s potential for farming is advised against.
You can farm corn and watermelon as a part-time hobby for your own personal pleasure, but do not expect to be producing enough to make any money. Whether it is your first time growing in a high tunnel or not, growing a marketable amount of produce is a full-time job. Hobbyists just will not have the time to keep their crops alive.
In short, planning to farm enough to make money means planning to cut other hobbies or business interests out of your life. If you are prepared for that then Godspeed, but no one can or should advise you to do such a thing to your lifestyle.
Difference #5: What They are Made Of
This is the factor that affects the cost difference of greenhouses and high tunnels the most.
Because high tunnels are open-faced and do not need to be sealed like greenhouses, they can usually be made of very cheap material. The most common is polyethylene, with steel supports to keep the arch of the tunnel stable.
Polyethylene can also be used to make greenhouses, but its frailty makes other materials better suited to the job. That frailty does not make the material useless, however. It means that it will not break in heavy wind or harsh weather, but instead bend.
The low cost of buying polyethylene has less to do with its quality as a material and more to do with how easy it is to produce. Compared to the glass of a greenhouse, it is a far less complex material.
While greenhouses do not always need to be made of glass (there are plenty of viable plastic substitutes that work just fine) they need to be more durable and denser in order to accomplish the goal of sealing them off from the outside world.
In short, greenhouses’ materials will make them more expensive than high tunnels. This is almost universal. In fact, you would have to build or buy a pretty large high tunnel before its price started to rival that of a modestly sized greenhouse.
The reason for the differences in materials comes down to the previously mentioned differences in purpose. High tunnels simply do not do as much to manage their plants’ environment as greenhouses do.
High tunnels also do not need to trap the heat created by light like a greenhouse does. When a greenhouse lets light pass through its glass panels, that light then strikes the inside of the greenhouse. It bounces off the inside of the greenhouse as infrared radiation, which is ultimately what makes the greenhouse warm.
Without the glass insulating the greenhouse, this heat would escape. Lacking insulation and being open-air means that high tunnels do not trap heat as much. If this sounds like a massive drawback, keep in mind that this also puts greenhouses in danger of overheating.
It is one of the great struggles of greenhouses: Their design allows them to reach heats that nature would not normally allow, and in environments where it normally would not be possible. But this comes with the risk of overheating, and in the process drying out the plants.
High tunnels only need to worry about that if the conditions of the environment around them are threatening a draught.
For that reason, if you live in an area with frequent draughts (like LA or southern India), then greenhouses might be preferable. Sure, they run the risk of drying out at all times, but it is for that reason that tools have been developed to manage that heat.
This is where the cost of greenhouses really goes, as suddenly the materials that constitute them are not just glass panels and pots for plants, but also the vents and misters that keep their plants alive when the heat gets too much.
And if you are wondering if high tunnels have similar technological features…
Difference #6: Technological Features
As mentioned before, greenhouses have the big feature of being able to control their environments with a number of different tools. In addition to the vents and misters, they can also install LED lights that are specifically tuned to the wavelength for best stimulating the growth of their plants.
They can install sensors that detect the temperature and humidity in the air in order to activate other devices to manage these things. They can feature automated shades that cover parts of the greenhouse that are overheating at certain times of the day.
Almost any climate-related problem you can imagine, there is a solution that someone can sell you.
High tunnels do not have as much modernization, but they are not without their features. The biggest is irrigation. Greenhouses have access to irrigation, but it works a bit differently in high tunnels.
Irrigation is really only required for especially large high tunnels, but it is worth mentioning as there are more affordable irrigation options on the market than one would expect.
High tunnels are bigger and can house plants and crops that occupy more space. Due to this, they can also house growing technology that would seem impractical to try and fit into a greenhouse.
Greenhouses have to stay sealed, so their irrigation will usually (though not always) have to be miniaturized to fit inside the greenhouse itself. Not so with high tunnels, due to the fact that they are open-air, irrigation can be as large and unwieldly as they want.
In fact, high tunnel irrigation can be so massive that it does not fit inside the high tunnel. This is not recommended for first-time growers, obviously, but some farms will grow fields and fields of one crop, interrupted by a small stretch of another crop grown in a high tunnel.
The irrigation pipes, however, will still run through the high tunnel uninterrupted.
Similarity #1: They Both Work
Greenhouses and high tunnels are different in many ways, but it should be known that these differences are essentially a matter of purpose. High tunnels grow large crops better, while greenhouses accelerate the growth of anything smaller better.
If you are looking for getting into gardening for the first time, a cheap greenhouse will teach you a lot. A high tunnel, meanwhile, will be much cheaper and certainly will not ask as much of you.
If you are an experienced grower, then you likely know your needs well enough to decide what is best for you from the factors already mentioned. Hopefully, you choose wisely, grow healthily, and have fun while doing it.