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Top 20 High Tunnel Questions Answered!

High Tunnels are becoming popular with growers of all skill levels for many reasons. These growers see high tunnels as a step between field growing and greenhouse growing. High tunnels are a great way to extend your season, increase yields and minimize pest and weather-related issues. Many of our customers here at Growers Supply have taken an interest in high tunnel growing. Here is a list of common questions we hear from them.

High Tunnels

Tomatoes and lettuce in a high tunnel1. Is there a size limit to these structures?
There is no size limit. We do offer certain sizes that are standard, however since we are the manufacturer, we can make anything you need or want.

2. Do you recommend many small structures or one large one?
It depends on the crop that you’re growing. If you’re growing one crop and you want to keep it all together, you will be better off with one large structure, like a gutter connect high tunnel. Otherwise the small structures create individual micro-climates, which make it easier to control pests, watering, sunlight and more for individual plants.

3. Can these structures be expanded?
Yes, but it’s much easier to expand lengthwise rather than widthwise. Lengthwise, once you have one high tunnel, you can keep adding on infinitely and make the structure as long as you want. The width is a little bit harder to manage because of the fact that you need to stand them next to each other or connect two structures together to make one.

4. Is there a limit on length for manual roll-up sides?
Technically there is a limit, because the longer you go, the more strength it will require to roll up the sides. The longer the roll-up sides, the more difficult it becomes to roll up the sides easily or keep them level. We don’t recommend going any longer than 96′.

5. Is the fabric covering better for the South?
Premium Round Style High Tunnel with Shade ClothThe fabric covering will filter out more of the sun, so in the southern portion of the United States, we do recommend using the fabric cover so that your tunnel will stay a little cooler. It is more difficult to cool a tunnel than it is to heat a tunnel. In high desert areas or in the southern portion of the United States, we recommend the 5.2 oz. clear fabric. It is a translucent material that will let in approximately 85 to 88% of the sunlight through. You will still have adequate lighting for your plant needs, but it will help cut down on the heat.

6. Which models are best for the Northeast?
The best model for the Northeast is the Premium Round Style High Tunnel. These tunnels have rafter spacing of 4′ and the pipe size is just under 2” in the 30′ wide size. With this model you get a roll-up Gear Box so you can open the sides easily and the end panels are made of the 5.2 oz. fabric.

7. What is the difference between the roll-up and drop-down sides?
The main advantage of the drop-down sides is where the air comes into the house and the temperature of the air. If you are growing in the ground and you open the drop-down sides, the cold air will come in above your plants and as the air becomes warm it will rise. The plants themselves are not exposed to the cold air. Roll-up sides are a little bit easier to maintain and last longer because as you roll them up, they are off the ground and out of the way. Since drop-down sides are on the ground when they are in the down position, they have a tendency to collect water and get dirty. The main disadvantage of roll-up sides is early in the morning when you open the tunnel, cold air comes in at plant level. There is a chance that you could cause some damage to the plants if the air is too cold.

8. What size high tunnel do you recommend for someone just starting out?
It depends on what your budget is and how much space you have. We have never had anyone complain that their high tunnel was too big, but we have had people call back and say that they should have bought a bigger tunnel. One of the great things about high tunnels is that because they don’t use electricity, the initial cost is really the only expense. It is not unusual to recoup the amount of money that you spent on the high tunnel within the first year or two.

Installation

High Tunnel 29. How deep do the anchors need to be? Does increasing the anchor depth reduce the number required?
Our ground posts are 36″ long and we recommend that they are driven 30″ into the ground, leaving 6″ to anchor your rafters to. Increasing the anchor depth does not reduce the number of anchors required.

10. How important is it to build your high tunnel on a level surface?
The more level the surface, the better and easier it is to tend to the plants inside. However, if it is on a surface that is not level, it will help with water runoff.

11. What methods do you employ to install the anchoring system?
The ground posts that come with the high tunnel have a ground post driver included with them. It looks almost like a steel mushroom. Insert the ground post into the driver and use a sledge hammer to drive the posts into the ground 30″. This is done every 4′ or 6′ depending upon what model you purchase.

12. Is it recommended to use concrete when installing the anchors?
Concrete is always a good idea, especially with the longer tunnels. It is recommended that you secure the first and the last rafter, as well as one or two in the center.

13. How easy is it to take the structures down and relocate them to another site?
Very simple, all you need to do is unbolt the rafters from the ground posts, remove the cover, and move the structure to the new location. You can reuse the ground posts, but it might be easier to order new ones. Once the structure is relocated, install the ground posts, bolt on the rafters and put the cover back on.

14. Is there a benefit to having the high tunnel run north to south or east to west?
Yes, in the northern half of the United States, you want to run the tunnel so that it is east/west and in the South you want to run it north/south. The reason it is positioned this way is to take full advantage of heat and light.

Maintenance and Repair

High Tunnel - Roll-up sides15. How well do these structures stand up to high wind and snow loads?
Because these structures are not heated, if you get a lot of snow at one time you will need to be able to access the tunnel and remove the snow. We recommend round-style high tunnels for high snow-load areas because the snow slides off the sides better. As far as high winds, you may opt for the 5.2 oz. fabric instead of the 6 mil 4-year commercial-grade greenhouse film because it has a tendency to be a little bit tougher and stand up to the wind better. However, it’s not unusual for our high tunnels to be exposed to high winds and not have a problem.

16. Are any of your high tunnels rated for snow loads?
If you want your building rated for wind and snow loads we can do that for you, but it is not something that is done routinely on high tunnels. The reason we don’t is because the only way you can determine an accurate wind and snow load rating is if you get stamped drawings from an engineer certified in your state that says the high tunnel is wind and snow load rated. We also don’t control what foundation is used and the foundation can have a big impact on wind and snow load ratings.

17. Does the galvanized steel rust?
No, galvanized steel does not rust. All of our steel is American made and triple galvanized. Triple galvanization is a process in which the inside and the outside of the steel are coated. The frame itself has a 3 year warranty, but because of the galvanization you should not see any rust whatsoever.

18. What is the lifespan of each fabric and film?
It depends on what area of the country you’re in, but you should get 5 to 7 years from the fabric. The film is a commercial-grade 4-year 6 mil film. The film is UV stabilized for up to four years. Over those four years the UV protection is used up and the film will yellow and become brittle. You may get longer life out of the film, but it is best to replace the film every four years to maximize your UV protection. The main difference between film and fabric is the amount of light that is transmitted. The film has 92% light transmission and the fabric has 85 to 88%.

19. Do you offer repair kits?
We offer two types of repair tape. Use Fabric Repair Tape if your high tunnel is covered with fabric and Greenhouse Premium Repair Tape if your high tunnel is covered with film.

20. Do you recommend taking the fabric or film down during the winter months for high snow-load areas?
If snow accumulates on your high tunnel, you will want to do one of two things. Either remove the film so you don’t have to worry about the snow or go inside the high tunnel with a soft brush and just give it a little tap. It more often than not will slide right off. In our experience, we’ve found that the snow slides better on the round-style rather than the gothic-style high tunnels. If you keep your eye on the high tunnel, you shouldn’t have a problem.

High Tunnel Growing can be fun and extremely rewarding once you understand what you are doing. If you are looking into high tunnels for the first time, or want some advice for using the high tunnel you already have, contact a National Account Manager who will have all the knowledge you need for a successful harvest.

Is there an important question we missed? Let us know and we will work on getting an answer.

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