9 Benefits of Growing in High Tunnels

If you’ve been thinking about adding a high tunnel to your farm or garden and are wondering if it’s worth the hassle, join small-scale farming expert Jenna Rich as she discusses key benefits and some drawbacks to help you decide if this step is right for you.

A view of a high tunnel hoop house. It is a semi-circular structure with metal hoops supporting a translucent, polyethylene plastic. Inside grows a variety of vegetables in different growth stages. The vegetables have leaf sprouts in various shades of green.

Contents

I’ve grown vegetables and flowers in high and caterpillar tunnels for six years. We’ve seen a significant increase in our plants’ survival and decreased disease and pest pressure. We’ve extended our season on both sides of the year.

We will continue to add more tunnels to our growing operation to keep these benefits going. There are initial expenses and maintenance throughout the year, but I think they’re worth it.

Environmental Protection 

Rain, snow, wind, hail. These are just a few weather events that happen throughout the year that crops need protection against. High tunnels will protect your crops all season long from anything happening outside. 

Early Season Weather

A polytunnel covered in a fresh blanket of overnight snow. The white snow contrasts with the tunnel's translucent covering. Trees surrounding the polytunnel cast shadows, creating a picturesque scene.
These structures provide a sheltered, warmer environment for early crop growth.

Plants are most vulnerable to environmental stress and damage during the first few weeks after emergence or transplant. The added warmth, nurturing, and calm air that comes with growing inside will drastically improve your spring crops’ overall health.

You’re probably familiar with the information on the back of seed packets and the note about soil temperature. Some seeds will not germinate in soil temperatures below a certain degree, so this is important information to note.

However, ground soil and ambient air temperatures are warmer inside the tunnel. With the added circulation from fans and ventilation, frost has a harder time settling on plants, and the lack of harsh winds gives these plants a stable environment to start their lives. 

Late Season

Three small polytunnels display semi-circular structures with metal hoops. Their coverings are made of translucent polyethylene plastic, allowing soft, diffused light to enter. Surrounding the small polytunnels are rows of plants in various stages of growth, adorned with vibrant green foliage.
Use for winter crop protection against frost.

Plan your sowings to include a late summer planting in your tunnel to protect crops against fall temperatures and impending frost. As long as crops are well-established by the time the days begin to shorten, you can grow in your tunnel all winter.

Growers in areas experiencing late-season rain from passing through tropical storms and hurricanes will benefit greatly from protection. 

Climate Change

Two high tunnel greenhouses are hit by sunlight. This showcases their translucent polyethylene plastic covering and creates a striking contrast with the surrounding landscape. The structure appears large and curved. Surrounding plants can be seen outside of the high tunnel greenhouses.
Climate change requires a shift in food production methods.

Due to the continued warming of our planet, experts predict that drought conditions and periods of torrential, damaging rain will be frequent and more intense in the coming years. Unfortunately, this puts us in a position of shifting our ways of growing food and adjusting our expectations of rainfall and regional temperatures. 

Growing in protected space is the only way for people in some parts of the country. While there is an added risk of tunnels getting damaged in large storms that may occur, the benefits of having one outweigh that risk. 

Extend The Season  

Spring

Various crops begin to thrive in a high tunnel greenhouse during spring. The translucent covering filters soft, diffused sunlight, casting a gentle glow over the lush vegetation. Rows of well-tended plants display a tapestry of shades and textures, signaling the season of renewal.
Benefit from warmer early spring conditions.

No matter what zone you grow in, I bet you get antsy when the birds start chirping, and the snow melts in the spring. I know I do. Imagine having a space that’s much warmer than it is outside on a sunny day, with beds prepped from the previous fall. Weed-free and amended soil just begging to be planted into – you could be direct-sowing cold-hardy spring greens as early as February! 

If you sell your crops, growing in a high tunnel allows you to offer high-valued crops earlier in the season than others, and you can charge top dollar for them because they’ll be, as we say, “first to market.” Building your tunnel efficiently to keep the frost out, and with the addition of row cover, you should be able to sow seeds a few weeks earlier than you would outside, which, for something like 24-day radishes, you’re a whole succession ahead! 

Fall

A view of empty plant beds in a polycarbonate greenhouse during fall. The rectangular plant beds are filled with vibrant brown soil. Small sprouts of green leaves can be seen in the soil. The diffused sunlight filters through the translucent walls and roof of the polycarbonate greenhouse.
Extend the growing season for heat-loving crops.

Growing in a high tunnel can also extend the fall season, allowing heat-loving crops to thrive even as days shorten and nights cool. With the addition of a row cover and closing up the side walls and end doors, there will be enough heat inside the tunnel to keep tomatoes, peppers, and even cucumbers happy. 

Bonus for spring and fall: If you are growing in warmer climates, you can still offer protection from the wind and elements, and you can cool the space by covering your tunnel plastic or individual garden beds with shade cloth. This will allow cooler weather crops to be grown even in warmer climates with success. 

Control The Internal Environment 

A view of high tunnels with different cultivars on a farm. The high tunnels are long, semi-circular structures made of metal hoops. They are covered by translucent polyethylene plastic. Green leaves from trees can be seen in the background.
Customizing allows for precise control over the environment.

One of the greatest things about tunnels is you can customize every part of them, allowing you to create a perfectly controlled environment for your crops.

Glazing

Glazing is the material that encases a high tunnel, typically a six-mil polyethylene. The plastic does not have much of an R-value, so it doesn’t hold heat effectively. You can install a double layer of poly separated by a blower fan to add more insulation. If you’re a northern grower, double-layered poly creates a puffed-up mushroom effect that helps shed snow load.

Insulation

Just like in your house, proper insulation can keep you warm and cozy when it’s cold outside and cool and comfortable when it’s hot outside.

Foam boards can be buried along the perimeter before installation. The foam creates a barrier that will decrease the possibility of frost inside your tunnel by blocking some of the cold air and keeping frost out.

Temperature

Any building can be heated. Just keep in mind the cost associated with doing so. When you run a heater in a single-poly tunnel, you heat the air, and that hot air goes right through the plastic.

Many growers have heat systems but only use them at the coldest parts of the year or have minimally heated tunnels set to a comfortable ambient temperature. Heaters commonly used are Modine style and run on propane.

A way to avoid the need for excessive and expensive heat is to grow crops that can withstand spring and fall temperatures in your region and use row cover along with biodegradable plastic to help heat the soil before planting.

Ventilation

This allows inside air and outside to be exchanged, keeping a fresh supply for your crops, decreasing humidity, and replenishing carbon dioxide used during photosynthesis. Ridge vents, exhaust fans, and roll-up side walls allow proper ventilation.

Circulation

Horizontal air flow (HAF) fans play a key role in moving air around so that all crops receive a similar environment. Adding at least a fan in two opposite corners blowing the opposite directions will suffice for the average-sized tunnel. More fans might be necessary if you have a large tunnel.

Circulation helps to move around the recycled air your ventilation system provides. If there is ventilation with no circulation, some areas of your tunnel will not benefit from the ventilation.

A study conducted at the Appalachian State University in North Carolina concluded that the “frequency of freezing and overheating events in the greenhouse was reduced significantly” when all the above techniques worked together.

Grow Vertically

A view of green and red tomato plants inside a plastic tunnel greenhouse. The fruits look plump and fresh, separated by an aisle of brown soil. A fallen red tomato can be seen at the side of the aisle.
Provide added height and structural support with various trellising systems.

If you’ve grown tomatoes, peppers, eggplant, or cucumbers, you’ve probably tried many different types of trellising systems. A high tunnel gives you added height and structure to work with and strength and durability to support a trellis system. 

A few options for trellising include:

  • Dropped string or jute
  • Roller hooks
  • Tomahooks
  • Lower and lean wicket system

Some sort of wiring system that runs from one gable end to the other gable end of the tunnel that runs directly over the beds you want to trellis will be necessary. This will give you something to hook or tie onto and offer added support for the weight of the crops. You’ll also need hooks that connect your crop vines to the trellis system and support them as they grow vertically. 

High tunnels can be as tall as 20 feet, so your tomatoes can grow a lot taller than they could if they were just outside, which means they’ll have the support they need, and you’ll be enjoying the fruits of your labor much later in the season. 

Bonus: When you are encouraging your crops to grow vertically and heavily pruning the bottom as they grow, you can take advantage of the space along the sides of the garden beds for an additional crop such as lettuce, basil, beets, or a natural pest deterrent like marigolds or green onions. 

Contain Diseases

A close-up view of a red tomato afflicted by disease. Its once vibrant green leaves now display discolored patches that are yellowing and browning at the tips. The leaves are wilting and drooping.
Benefit from close crop monitoring, enabling early disease detection and control.

Growing in an enclosed space allows you to keep a closer eye on crops than those in your field. Why? Because odds are, you’re growing high-valued crops in there and will be in and out more frequently than just walking through your outside garden beds. You’ll notice little changes happening to crops, such as small, yellow spots creeping up your tomato leaves, powdery residue on your basil, or drying up leaves on your cucumbers. And when that happens, you can swiftly take action. 

When your plants catch a disease early and you can properly identify it, you can control the spread much easier than if it were outside. Think of it as keeping yourself in a separate room from your family members when you have a bad case of the flu. Our tunnel tomatoes contracted Septoria leaf spot this past summer, and we noticed the symptoms very early. After contacting our extension office for advice, we sprayed our tomatoes thoroughly with a fungicidal copper spray and then again two weeks later, and the issue was resolved! 

Many diseases, such as late blight, thrive in wet, humid environments, making a closed-up tunnel a somewhat risky place. However, drip irrigation lines can keep water from splashing up onto the leaves of crops, decreasing the risk of disease.  

Reduced Pest Pressure 

Solar-powered repellent tool in foreground view between growing red and green tomato plants. The repellent tool and tomato plants are inside a greenhouse covered in polycarbonate plastic.
A high tunnel can reduce damage and lower pest populations.

So there won’t be any pests inside a high tunnel, right? Well, no, not exactly. However, similar to reduced disease pressure, you will likely notice pests sooner than outside because you’ll walk through the tunnel more, scouring for any issues.

Pests can also include mice and voles looking for a warm place to hide in spring, fall, and winter. Take extra caution when using silage tarps. Voles love the extra heat and protection they offer. 

As a caveat, pests can seem more of an issue because of the confined space and the plethora of crops to munch on. Still, if you break their life cycle, keep weeds down, and use protection like insect netting against pests, you will see less damage and, eventually, fewer pests altogether. 

Reduced Weed Pressure

A view of tomato plants with lush green foliage tied up to timber frame wood. They look orderly and upright in mulching soil. A gallon of water can be seen nearby.
Using mulch and composted beds is crucial to controlling weed pressure.

Heavy mulch and composted beds are key regarding weed pressure. Mulch options are straw, black plastic, biodegradable plastic, and aged compost. You can also use the white side of a silage tarp to keep your paths covered. 

Mulch in the fall before you close up your farm or garden for the season. Keeping weed pressure down over the winter will have lasting positive effects on everything throughout the year, including weeds, pests, and disease pressure. 

Netting can be installed along the sides of your tunnel to reduce weed pressure the same way you can for pest protection. It won’t stop all the seeds, but it may decrease the amount of weed seeds blowing in. 

Increased Quality and Yields

A polytunnel with long rows of strawberry plants. The plant leaves are vibrant green under the diffused light of polycarbonate plastic.
Crops in protected environments yield higher-quality, healthier produce.

Crops grown under protection will most often be of a higher quality, having less environmental and cosmetic damage, so you can charge top dollar for them.  

Plants grown in tunnels will not only look better but will be healthier. Production and yields will increase, giving you the most bang for your buck. If you’re one to intercrop inside the tunnel, you can get multiple crops out of one bed. For example, if you grow tomatoes in your tunnel, which are in the ground all season, plant parsley, basil, beets, or green onions along the outside edge of the bed. This style of intercropping will help suppress weeds, double the production in the high-valued space, and might even serve as a pest deterrent. 

Once you figure out how to effectively manage pests and control disease, crops inside your tunnel will be as close to perfect as possible!

Customize For Your Ergonomic Needs

Rows of organic kale in a high tunnel show different varieties of genus, growth, and shades of green. The rigid-framed high tunnel is made out of metal and polycarbonate plastic.
Customization improves your growing experience.

I’ve already mentioned the components, such as glazing, insulation, and heating options of a high tunnel, being very customizable. Still, you can also build it so the functionality fits in with your ergonomic and lifestyle needs. 

Here are a few examples of lifestyle concerns and an easy solution you can build into your new building:

  • Don’t like the idea of rolling up the heavy sides by hand?

Install an easy hand crank roll-up. This may take a few seconds longer, but the crank will take some strain off your back by doing the work for you. 

  • Are you renting your garden space, and aren’t there at first light or in time to close up at night? 

There are automatic roll-up options set to a specific time or internal temperature so you can set it and forget it. 

  • Want to use the wall space to house garden transplants in the early season or to store supplies over the winter? 

You can build temporary shelving units that simply fold up and lock into place or fold down when not in use. Do this at the top and bottom for easily accessible storage space. 

Pro tip: Use wall space by hanging magnetic strips to hold your garden snips, harvest knives, and shears. 

Downfalls

I think the benefits of growing in high tunnels outweigh the cons. However, I would be remiss not to mention a few drawbacks here. 

Salt Buildup in the Soil 

Close-up view of a farmer using a soil pH meter to check the pH value of an organic plant nursery farm. He is wearing a silver watch and beige pants. Vibrant green leaf sprouts emerge from the coarse brown soil.
Managing soil salinity in high-tunnel agriculture requires prevention.

This is a growing concern for growers using their covered space for 5+ years, as the effects will not likely be serious until then. Some crops are more sensitive to soil salinity than others, but it can decrease yields, cause yellow and brown tips on plants, and cause slower and decreased overall growth. 

Here are a few ways to control salt buildup in your high-tunnel soil:

  • Prevention: Add only what you need to your soil when amending. This ensures build-up does not occur and negatively affect your crops.
  • Cover cropping: Grasses tend to scavenge for available nutrients in the soil, which may help to clear out any nutrients that are in excess and negatively affect crops the following season. Grass-cover crops like Japanese millet, wheat, and rye are perfect for wintertime in the tunnel. Just be sure you have a plan for termination in the spring.
  • Water management: Take advantage of the rain and snow when you can! If it’s time to replace the plastic on your tunnel, take it off in the fall to allow rain and snow melt to leach salts down through the soil, past the root systems of future vegetable crops. This is an inexpensive and relatively quick way to mediate soil salinity.
  • Soil test: This is a must, especially if you have concerns about soil salinity. These results will give you a baseline idea of what your soil needs and what it might have too much of. Furthermore, most soil test results will provide recommendations for amendments.

Need For Irrigation System 

A view of black hose for drip irrigation system inside a greenhouse. Small green pepper plants are mulched with dry grass. The plants are short, yet show good growth health.
Effective irrigation is crucial.

Bringing on the rain with your backyard rain dance won’t help out the crops in your high tunnel, so an irrigation system must be installed. This can be as simple as using a hose and sprayer wand, but drip irrigation lines will be most effective

Drip irrigation provides deep root watering and helps avoid water splash to decrease soil-bourne disease. Grab a couple of sprinklers or wobblers if you also want the option to overhead water. 

The best thing to do is look online or locally for a reputable garden supply store. Kevin has used Drip Depot and other reliable, reputable suppliers over time. Check out how he updated the drip irrigation in one of his older raised-bed systems in the following video.

 

Pollination Issues 

Close-up view of bumblebee pollinating flowers in a greenhouse tomato crop. The flowers have bright yellow petals and hairy stems.
Ample pollination is essential for quality fruits in high tunnels.

Ample pollination leads to better quality, large fruits. If you add insect netting to the sides and doorways, decreased pollination may become an issue. Don’t worry, though. Researchers have been working on this and have found at least four recommended ways high tunnel producers can help their crops get pollinated. 

  • Tapping strings or wires: This method agitates the plant and flower, signaling it’s time to release and receive pollen. This works best in small operations or backyard gardens and can be done about every three days.
  • Gardening vibrators: This works similarly to tapping of strings but is a little more intense and effective. Do this every other day.
  • Air blowers: This takes less time but results in smaller fruit, perhaps because the airflow is too intense and pollen is being blown off the plants. 
  • Bumble bees: Some growers install a bumble bee house directly in their high tunnels to ensure proper pollination. Be sure to order from a reputable source if you go this route. 

You can also hand pollinate your crops without much effort.

Cost of Initial Infrastructure and Maintenance 

A view of a polytunnel under construction. Plant beds haven't been made yet. Green grass is scattered on brown soil. The Quonset hut building has metals sticking out inside the polycarbonate plastic.
Costs vary depending on size and features.

There’s no way of getting around the truth: these structures are somewhat expensive to purchase, install, and maintain. There is a wide range of options and advanced features, so you can spend as little or as much as your budget allows, and it’s really all about perspective. How much will you save by growing your own food, and how long before you make a return on investment (ROI)?

On average, the cost of a new high tunnel in 2023 is about $6.72 per square foot. Remember that the cost depends on everything, including the brand, the materials used, and labor. A small tunnel in a backyard garden may be 14×30’, whereas a large-scale operation may feature one that’s 30×96’. 

You can choose between a classic rounded-shaped tunnel or gothic-style, which many northern growers select due to its ability to shed snowfall. They should be at least six feet tall in the center for ease of working inside. All of these features have different costs involved, and different materials that companies offer can alter the cost even further. 

Things that will need maintaining:

  • A roof rake. If you live in a region that receives heavy snow loads, you should invest in a roof rake and pad it out with something soft. Use this to remove snow that does not slide off your tunnel so the plastic does not cave in.
  • Polyethylene (high tunnel covering) will break down and yellow over the years, and depending on your growing region and the amount of direct sunlight it endures, the film should be changed every 4-5 years. Any longer, and it may affect growth inside.
  • Keep your eye on the wood used along the perimeter of the tunnel. It may shift over the years and need replacing.
  • Random nuts and bolts that hold everything together, specifically along the hip boards.
  • Doors may sag or need tightening up as the wood swells from the weather.
  • It’s a good idea to stain or clear coat if using untreated wood for end walls to extend the life.

Tips For Overall Growing Success

A green pH meter is used to measure the level of alkali in the ground for plants. It shows that the current level is relatively dry. Covered soil is seen in the background with a few green plants protruding.
Optimize high tunnel gardening.
  • Create a watering schedule and stick to it. Use a moisture meter every week during your first year to learn how often and how much you need to water so your crops have ample moisture. 
  • Keep records. This is important for growing anywhere. This should include pest activity, weeds, moisture levels, temperatures, etc. 
  • Take advantage of growing space by limiting walkways. 
  • Clean up summer and fall crop debris, manage pests, and terminate weeds before winter so you’ll have a clean spring tunnel. Weeds can harbor disease and pests all winter, creating a disastrous future situation. 
  • Get an outdoor thermometer to keep track of the difference from outside to inside the tunnel. 
  • Be careful moving from any area of disease to another to avoid spread. 
  • Use insect netting and row cover. 

Additional Resources

A tractor in an orange vest and a red mower is driving inside a high tunnel. The high tunnel made with metal and polycarbonate plastic is empty. There are no plants inside, just dried brown grass.
Before installing, consult local experts and explore grant opportunities.

If you are considering installing a high tunnel on your property, speak with local experts. You may even qualify for grants to cover some or all costs

  • Are you ready to add a high tunnel to your backyard or farm production? Check out the USDA EQIP Program to see if you qualify and how to apply. 
  • The National Resources Conservation Service (NRCS) can offer a wide range of assistance, including help growing in wetlands, conserving water, drainage grants, pollinator patches, and soil health, all of which may be useful. 

Final Thoughts

Purchasing, installing, and growing in high tunnels requires updated education, a different way of growing and scouring for pests, and maintenance throughout the whole year, during and after the season. However, the return on investment is high. As we all experience continued weather pattern changes caused by climate change, dealing with the challenges of growing in a protected space is worth it once you see the great results!

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