Growers Supply

Greenhouses vs. High Tunnels Webinar

Questions & Answers

Greenhouses and High Tunnels

  1. How is a high tunnel shipped?
    High tunnels are shipped on a pallet by a freight carrier. The majority of the country uses Conway freight and you do need to be there when it arrives to sign for it. It's easiest if you have something with forks to get the pallet off of the truck, but some people back their pickup up to the truck and pull it off that way.
  2. I have the finances to purchase a high tunnel now, but I would not use it for a year or more. How much will the film and frame deteriorate if I keep it boxed for that length of time?
    The benefit of buying a high tunnel now is that you know what the price is now. There have been a few increases over the last few years because of the steel market. It has balanced out, but 2010 was rocky; the steel prices went up precipitously. If you have the budget for it, buy it now. You can keep it palletized until you're ready to build it. Make sure to tell us when you place your order that you won't be using your structure right away. We will send you the poly on a rounded core instead of folded up which will prevent it from weakening at the folds. Make sure to store it in a garage or barn away from light. UV light is what really breaks film down.
  3. Will a high tunnel stand up to the high wind gusts and snow loads of an Alaskan winter?
    Yes, we do a number of high tunnels for customers in Alaska. We've actually worked with the state ergonomist and made suggestions to them. We have several options with rafter spacing and support packages and can absolutely meet your needs.
  4. What is the difference between the Gothic Pro and the Round Premium tunnel?
    The Round Premium tunnel has a rounded style frame, 4' rafter spacing, roll-up sides and zippered end walls. The Gothic Pro model has straight side walls and a peaked roof. The Gothic Pro models are also sold a-la-carte, so you have a lot of options regarding covers, roll-up or drop-down sides and end walls. The Gothic Pro is ideal for people who want to mix and match features. The Round Premium is popular for people who want to buy a full kit.
  5. Do you have videos that show a high tunnel being constructed?
    Yes, we have several videos available on our YouTube channel. You can also contact us. We have several customers who have sent in their videos and blogs of constructing our high tunnels.
  6. We just put up your Round Premium High Tunnel. What is the easiest way to roll up the ends of the tunnel?
    The easiest way is running the center and side zippers straight up. If you are having trouble reaching the center, use a zipper extension pole, which is essentially a 5' pole with a rope cleat on the end of it that will help you pull the zipper all the way up. To roll them up you will need a ladder, but for the most part, you will not be raising and lowering your ends that often. Once the weather gets warm, you roll them up and pretty much leave them that way for the whole season.
  7. What is the ground post size of a high tunnel?
    All of our ground posts are 3' long. These are driven 2-½' into the ground and your rafter leg slides over and bolts into the exposed 6". The gauge and diameter of the ground posts is going to be based on the gauge and diameter of the rafters. For instance, if you have a 2" rafter your ground post will be slightly smaller so your rafter can slide over and bolt to it.
  8. Would you recommend a greenhouse or high tunnel for aquaponics?
    It depends on what fish you are growing and what method you're using. The trick with aquaponics is you need to maintain warm water temperatures for the fish without exceeding certain air temperatures for the plants. Generally, a greenhouse is better because you will need to run heaters and fans to balance those temperatures.
  9. Do you have to close the tunnel at night?
    That depends on how cold it's getting at night. Use a Hi-Low Memory Thermometer to see what the temperature is getting down to. From there it is crop specific.
  10. What is the minimum height of a high tunnel?
    That's a great question and to give you a little bit of history, high tunnels came from cold frames which developed from low tunnels. Many years ago folks realized that throwing a frost blanket over their crops provided a few extra degrees of temperature control. Certain crops didn't do well with a frost blanket resting directly on them, so people started bending wire over the crops and resting the fabric on that, creating low tunnels. The low tunnels worked so well, people wanted to make them bigger and low tunnels evolved into cold frames. Cold frames can span 8', 10' and even 12' wide. As engineering improved, cold frames became high tunnels that span up to 35' wide. When you ask about the minimum height of a high tunnel, I have structures as short as 6' and as tall as 15' in the center. The height is often driven by the width.
  11. How do I pollinate plants inside of the structure?
    A lot of commercial growers buy boxes of bees. They are pretty easy to find this time of year. If you do buy bees, when they are shipped to you poke a few holes in the crate when it's in your greenhouse or high tunnel and let the bees do their thing. This method works extremely well. For those of you who don't want to bring in bees, another option is to plant wild flowers around the property where your greenhouse or high tunnel is. The flowers will attract bees and other insects that will pollinate your crops on their way to and from the flowers when you roll up the sides of your structure.
  12. Do you orient a high tunnel north to south or east to west?
    High tunnel orientation is different than greenhouse orientation and a lot of people confuse the two. You can follow some of the same guidelines, but the important difference is in a greenhouse you have fans doing all of your ventilation. In a high tunnel, you need to maximize your natural ventilation. Instead of thinking about north to south or east to west, think about where the prevailing breeze is coming from and if you are opening your side walls. If you are opening your side walls, you want the length of the tunnel oriented towards the prevailing wind so that the breeze keeps air moving across the high tunnel.
  13. I live close to your headquarters in South Windsor. Will you send out a representative to my property to give a recommendation on a greenhouse?
    We don't come out to your property, but if you come by our headquarters in South Windsor we have a number of greenhouses set up and we can have a conversation with you about what structure will best suit your property and needs.


  1. If covering a high tunnel with two layers of 6 mil film or fabric, is it better to put the first layer on and attach it with the spring wire and then add the second piece of fabric?
    It can be done both ways. One way to do it is adding the first layer of film and a spring, then adding the second layer of film and a second spring. However there are a lot of people who pull both layers of film over the tunnel and lock it in with one spring. Which method you use will depend on if you're using film or fabric. Two layers of film will fit with the double spring method, but if you're using fabric it may get a little tight, so using a single spring for both layers of fabric may be easier.
  2. Does the poly film hold up on the roll-up sides?
    It holds up very well. The roll-up sides will last as long as the roof. If there is a lot of wind, you may see some wear patterns where the film rubs against the rafters. If you have a problem, we offer Greenhouse Premium Repair Tape to get you through a season. Typically you will need to replace the film on both the roof and the sides every four to five years.
  3. What is the best way to attach 6 mil plastic to the high tunnel rafters to prevent tearing?
    Use U-Channels and spring wire. The channel is a 1-½" aluminum bracket which you screw down running the length of your frame, the plastic sits in the channel and the wire locks it down. The stock number for our U-Channel is 102197. When you look up that stock number, there is a flash video on the page where you can view the installation of this product.
  4. Do you need shade covering in summer for high tunnels?
    It depends on where you're located and how many hours of daylight you get. If you get straight sun all day, you will probably need to shade your tunnel. We have two types of shade. One option is an inexpensive paint-on liquid that will slowly rinse off with rainfall over time. We also have more permanent shade cloth that you pull over the high tunnel.
  5. What coverings have the greatest lifespan?
    If you're looking at a greenhouse, polycarbonate has the longest lifespan. The warranty will have you covered for 10 years, but you can realistically expect 15 years or more even with heavy UV exposure. Film is a little bit different. To get a longer lifespan from film, you will need to go with a thick material. The issue with this is that as you get into the thicker films or fabrics, you start decreasing the amount of light transmission rapidly. The 6 mil film has 92% light transmission. The 12 mil fabric has 85% light transmission. The next step up is 7 oz. fabric, which has 78% light transmission. As the fabric gets thicker, the light transmission drops, which can be an issue.
  6. How susceptible is the film to hail damage?
    If the film is tensioned correctly and you get small hail, it should bounce right off without damaging it. However if you get hail that is golf ball size or larger, you are going to get some damage. We have 4'' and 6'' patches so you won't need to replace the whole cover if your tunnel is damaged by hail. You can just patch right over the top.
  7. Do you have any more information on the 12 mil woven covering?
    The 12 mil is the 5.2 oz. clear fabric. It does quite well in heavy wind. We are happy to send you out a sample if you would like to see it.
  8. Are there any special considerations for attaching the 12 mil woven fabric to a high tunnel?
    No, we use the same method to attach the film and fabric. It is an aluminum channel that the fabric or film sits in and we use a spring wire to lock it in place. Both the film and the fabric have a four year warranty, but what we've seen in the field is that the fabric will last from five to seven years.


  1. Do you carry Flora-mist or Pin-Perfect nozzles, or any Netafim products?
    Yes, we do carry some Netafim products. In terms of Pin-Perfect nozzles, if we don't have them in stock we can special request them for you. We need to know the quantity you would need and the SKU number.
  2. Do you have plastic mulch with precut slits for planting vegetables and do you have equipment that lays the plastic or mulch in a trench?
    We do carry plastic mulch in number of thicknesses from 1 mil to 10 mil. None of it is pre-slit. The equipment to lay it out is usually an attachment for a tractor and we don't carry it.
  3. Do you offer insect barriers for the sides and are they strong enough to block other animals from coming in?
    Yes, we have a couple of products. One product is called Insect Netting, which is very specific to your question, but it does restrict airflow. That is important to think about when you're planning your greenhouse or high tunnel. We typically don't recommend full insect screening because it blocks so much airflow. Another solution is a lightweight shade cloth, but rather than using it to shade the tunnel you would use it to prevent the insects from coming in. The shade cloth will allow a little more airflow than the Insect Netting. Some of our customers live in climates where deer and small animals are rampant. They purchase hex netting or chicken wire and run it along the inside of the frame to prevent the animals from getting inside.
  4. Do you have a way to collect rainwater?
    Yes, the best way to collect rainwater is to install a gutter. To do this, attach the gutter with a very subtle pitch down the length of your structure and collect it with a rainwater barrel or a 55-gallon drum. You can use this water for irrigation. Recently we have had a number of organic growers buy our NFT channels for this purpose. They are required to use food-grade materials to harvest the water. Before you purchase the materials to collect rainwater, make sure to check your local laws because it is illegal in some states to collect rainwater.

Read our Greenhouses Buyer's Guide
Read our High Tunnel Buyer's Guide
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