The Use of Movable High Tunnels in the Organic Production of Strawberries, Potatoes, and Raspberries

Final Report for FNC02-387

Project Type: Farmer/Rancher
Funds awarded in 2002: $5,644.00
Projected End Date: 12/31/2004
Region: North Central
State: Wisconsin
Project Coordinator:
Expand All

Project Information

The Use of Movable ”high tunnels” in the organic production of strawberries, potatoes and raspberries

We own approximately 75 acres of land of which about 25 acres are tillable. The rest of the land is marshland and forest, which serves as a buffer from other farming practices by neighbors. We farm chemical free and have been certified organic for a number of years. We no longer certify as most of our customers know of our sustainable and chemical free farming practices and certification is no longer necessary. We primarily grow small fruits and vegetables, which we sell at the local farmers market.

Using organic growing practices, we are going to determine if it is feasible for the market farmer to use the “High Tunnel System” to increase the profitability of his crops by reducing his loss due to diseases, pests, and weather concerns, while at the same time extending the production season. (A high tunnel is a portable hoop type green house without heat that has rolled up sides to allow for natural air movement.) The focus will be on spring strawberries, new potatoes, and fall raspberries.

• The tarnished plant bug often destroys the marketable quality of well over 50% of my strawberry crop.
o The concept is that the earlier ripening of the strawberry crop due to the early warming of the soil by the high tunnel, should avoid the tarnished plant bug problem. (The berries natural blooming cycle coincides with the time when local farmers are removing their hay crop, causing the tarnished plant bugs to migrate to the strawberry field. Bringing the berries into bloom 3 weeks earlier should eliminate this problem.) The tunnel should also protect the berries from the danger of frost damage and from problems caused by excessive wet weather during ripening.

• The Colorado potato beetle and early and late blight have been a major problem on my organic farm creating excessive labor during a busy time of the year.
o By using the high tunnel with screening on the open sides, while the tunnel is over the potato crop, I expect to prevent the problems of the Colorado potato beetle and also reduce the potential of early and late blight by keeping the crop protected from wet weather.

• Fall Raspberries would be a great fall crop except that frost normally shuts down production before the main berry crop ripens.
o With the raspberries, I intend to prevent the usual loss of production due to frost. Often growers try to plant earlier ripening varieties to solve this problem. The advantage of extending the growing season with the frost protection produced by the high tunnel verses using earlier ripening varieties is that the later ripening is after most crops have been killed by the frost, thus reducing the farmers workload, and the customers demand for such products are much higher.

A major benefit is that this growing method spread out the workload of growing and harvesting these crops, resulting in less labor demand on the grower. At the same time, it should also extend the market for these products over a larger period of time, which should in turn bring a higher return and easier sales at the market. The High Tunnelshould increase marketable yield per plant, and thus reduce the amount of crop and labor needed to fill the marker demand.

We will be using the High Tunnel along with control plots grown using our usual organic growing methods. By using the two methods side by side on the same farm, where known problems already exist, we hope to produce accurate records of cost, production yields and marketability of the product. Doing so, we should be able to make accurate comparisons of the advantages and/or disadvantages of such a system of growing these crops.

The research will be done on three separate areas within the tunnel and three separate areas within the control plots to create an accurate analysis of the project. Both test crop and control crop will be planted in the same way with plastic mulch or leaf mulch and drip tape for irrigation.

We have an established market at the Stevens Point Farmers Market, where we have been marketing berries and produce for years. We feel we have a good degree of experience, which should help us to be able to evaluate the impact of this project at the market in regards to sales competition, consumer demand, and the social impact of this project, not only for the grower but also the impact this will have on the market by extending the crop season to reduce the glut of produce ripening all at once.

My children and I will be performing the bulk of the work so as to avoid adulterating the research because of possible changes of labor methods entering into the test result. This should ensure that any positive or negative results would be because of the use of the high tunnel and not new labor practices.

As is standard procedure, I Dan Mielke will be overseeing all work and data collection. Adam will be doing the bulk of the labor with my two daughters helping with planting, mulching, weeding, picking and sales of the crops. Robin, my wife, will handle the records, or sales and expenses, and oversee the marketing of the product.

Strawberry bed preparation and planting will take place in the fall using three varieties of strawberries. Each variety will be planted in three separate areas of tunnel locations and three separate areas in a control plot outside the tunnel. We will divide the crops between two separate tunnels, each having duplicate situations to help ensure data results in the event of tunnel failure or other unforeseen problems within a particular tunnel.

Note: Because all planting stock will be purchased new, the crop taken off will be sold as non-organic due to the rules set down in the National Organic Program that require the plants to be grown on organic land for a longer period of time than the study will allow, unless we can locate organic planting stock. This will not hinder the results of the research as we normally sell our organic products at the same price the conventional growers do anyway.

In the spring, the raspberry beds will be built and planted in the same manner as the strawberries above.

Tunnels will be set over strawberry beds in spring, as early as weather dictates to achieve a three to four week advance of normal crop cycle.

Upon completion of the strawberry crop, the tunnel will be moved to the potato bed that will be prepared just prior to placing the tunnel. Again, data will be taken from three separate areas in the tunnel and in the control plot.

In September, just prior to the frost date, the tunnel will be moved over raspberry beds and again, data will be gathered from three separate areas of the tunnel and the control crop.

Records will be kept of labor cost, quality, marketability, crop volume, and disease and pest damage difference in each crop.

Tunnels will reside over strawberries in April to June, over potatoes June to September, over raspberries September to end of raspberry crop.

Control crops will be allowed to progress through their normal ripening stages

Strawberries. Berries were planted in 2002, during the summer, in the late fall, and in summer of 2003. They were planted in double rows under white plastic with drip irrigation.

We began the growing process on 4/15/03 by lowering the plastic to accelerate the growth of berries. We needed no artificial heat during the entire berry season. We would put the sides down in the afternoon before sunset to hold heat in. In the morning we would elevate the sides to keep tunnel from overheating. One needs to be careful to not cook the plants and yet maintain an appropriate growing temperature.

We were exceptionally pleased with the results of strawberries grown in the tunnels.

1. Berries were cleaner
2. Very few deformed berries
3. Foliage stayed green and clean throughout the season
4. Berries were some of the sweetest berries we have ever grown
5. Size was excellent
6. Ripening of berries
a. Tunnel berries began 6/01/03
b. Berries in plastic mulch under floating row cover began 6/11/03
c. Berries without plastic mulch or floating row cover began 6/26/03

7. Quality
a. Tunnel berries were
i. Sweeter
ii. Cleaner
iii. Less distorted
iv. Larger
v. Less pest damage
vi. All three varieties did well

b. Berries under plastic mulch and floating row cover but not in tunnel
i. Fair quality
ii. Severe turkey and coon damage
iii. Suffered frost damage
iv. Large amount of distorted berries
v. Honeoye were only berries that produced quality berries

c. Berries outside of tunnel without protection of any kind
i. King berry blossoms all froze
ii. Flavor was poor
iii. Berries were soft due to rains
iv. Berries all came in at once due to heat
v. Competition was severe at the market
vi. Most berries went to waste because of sudden ripening
vii. Honeoye was only berry variety that produced quality berries

d. Production records of berries inside tunnel verses outside tunnel (Records were taken on the two test plots that were grown identically with only difference being the tunnel.)
i. Early glow showed a 200% increase in tunnel
ii. Honeoye showed a 380% increase in tunnel
iii. Jewel showed a 330% increase in tunnel

e. Production difference between two tunnels (Tunnel one had leaf mulch placed between the rows and Tunnel two did not)
i. Early glow showed a 22% decrease where no mulch was used
ii. Honeoye showed a 10% increase where no mulch was used
iii. Jewels showed a 50% increase where no mulch was used
iv. Berries began production and had heavier production in the beginning where no mulch was used.
v. Berry production peaked at the same time in both tunnels

f. Berries started previous summer, and late fall production record.
i. Tunnel one where leaf mulch was used between rows.
1. Late fall planting produced 42% of early summer planting
ii. Tunnel two where no mulch was used between rows.
1. Late fall planting produced only 11% of early summer planting.

Berry sales were excellent with the one exception that we could no fulfill demand. The berries were early, clean, large, extremely sweet and very aromatic which was noticed by the customers and commented on as being the best berries they have had. Picking was at a slower pace due to steadier ripening taking some of the stress out of picking.

Because of the Saturday Farmers Market, we time pickings to be on Friday. On two of those Fridays there was heavy rain. What a pleasure to be able to enter the tunnels and pick nice dry berries. Had the berries been outside of the tunnels we would have lost all those berries or at best would have missed our market day. In one area the ground was lower than outside of the tunnel and water did flow in and damage a few berries. A few times it was hot and humid within the tunnel during picking. Picking could be done earlier due to lack of dew on plants.

Raccoons and turkeys were a problem both inside the tunnels and outside until we used a portable radio. The test area out of the tunnels did not benefit as much from the radio. We assume the echo within the tunnel enhanced the effect of the radio. Lowering the sides at night also helped to avoid early morning and late afternoon raids by the turkeys as well.

We did not find any bees or insects during the first blooming of the berries. But we did see a large number of spiders walking on the blossoms. Later on we found that a very tiny type of bee and flies were quite active amongst the plants. Very few honey bees or bumblebees were observed. We used no mechanical pollination methods. A lot of the insects that did enter the tunnels seemed to get disoriented and were unable to find their way out. They would fly up and bounce off the top of the tunnel until they gave up or died. The bumblebees in the fall were able to enter and exit without getting disoriented.

We supplied about ½ inch of water per week during the fruiting season with drip irrigation. Possibly should have done more.

We observed no tarnished plant bugs until towards the end of the crop season within the tunnels. Outside the tunnels we did observe more insect damage. It seemed the early ripening avoided much of the typical fruit damage by insects.

In the tunnels we did observe a slight increase of slug damage and an increase of spittlebugs, but nothing of great concern.

Workload: One of the nicest benefits of the tunnels was the benefits to me labor wise. We found that the extra hours gained by using tunnels were the biggest benefit of all.

1. The tunnels extended my working window by about 60 days.
2. The tunnel gave me an extreme edge on marketing my crop.
3. The tunnel allowed me to reduce the acreage and amount of crops needed to accomplish the same goal previously sought.
4. The tunnel gave me more freedom to deal with weather extreme.
5. The tunnel allowed me to spread out the harvest times of my crops.
6. I was able to avoid most of the periods of glut where competition meant produce returning home from market. There is nothing worse than to have a good yield and not to be able to market it. This was virtually eliminated.

Potatoes. We could not screen out the bugs because the material we used for screening caused the tunnels to overheat. So we did not use any bug barriers. We found no marked difference between the tunnel and test crop outside of the tunnels. No blight and very little potato bug problems were observed on either test plot. This was surprising, as we have always had bug and blight problems in prior years. Potato color was excellent and size was acceptable. On a positive note, we did notice that our Yukon Gold potatoes were the best we ever grew and they had no hollow hearts. We may try some early potatoes next year, but not a whole tunnel full. Yields were the same in or out of the tunnels.

Raspberries. For some reason the berries ripened quite late this year. We did not get any ripe berries until September 26th. On October 1st the weather turned cold and our test plot outside of the tunnels froze destroying any hope of a berry crop. Being in the zone 4 area, this is a common problem with fall berries.

The berries within the tunnels however continued to produce up until November 2nd. There were two nights where we placed portable heaters in the tunnel. We used approximately 20 lbs of liquid propane total. The berries in the tunnels were of excellent quality and size. The flavor varied depending on the temperature within the tunnel. Sun and warmth plays an important part on flavor. If a grower is able, he could enhance his flavor by spending more time regulating the temperature during the day. I would elevate the sides during the day to allow for bees to enter and often that allowed the temperature to cool off too much. It is feasible to leave the sides down to maintain a higher temperature within the tunnels providing one does not let the temperature get too high so as to cook the berries.

We faced no wasp problems, as I had feared. The primary pollinators were small bumblebees, which did an excellent job. The canes kept blooming right up to the day the plants were killed by cold in November.

Production was good up until the end. The volume of berries on the plants kept increasing up until the day they froze.

We decided to let the berries freeze on the 2nd of November because the weather forecast called for continued cold for over a week, and we felt the cost of heating the tunnel at night would be too high to warrant continuing.

Turkeys were a big problem with the berries outside the tunnel. A transistor radio playing in the tunnel seemed to do the job of keeping critters out.

We gained 4 extra weeks of berry picking through the use of the tunnels.

The berries sold well and had excellent shelf life.

Tunnels: We averaged 30 man-hours to put up the tunnels including driving the anchor posts. Expect to add additional time if you have to assemble the hoops from pieces. While we liked the 26 x 96 foot tunnels better than the 20 foot ones, we did find them much more difficult to put up due to the added height. The extra 3-4 feet in height makes a big difference. But once up, the taller ones are much more comfortable to work in. We did not even consider moving the large tunnels and bought two new 20 x 96 foot tunnels instead. They were much easier to assemble and move in mid season. While they were not difficult to move we did find that the plastic did see some damage from the wobble wire and because we could not get it put back in the same area the cover was weakened. To move the tunnels to the new location took 25 man-hours. If I were to do it again I would look into some sort of tracking system that would allow the tunnels to be moved forward and anchored as a complete unit. To do this you would have to have a large level area to allow for such a move. Keep in mind that is has to be anchored very securely to the ground to resist wind damage.

• Some tunnels use self-tapping screws to assemble them. A battery powered screw gun is very useful during the assembly process.
• Drip tape works just fine when fed by a tank of water on a wagon. Actually it helps you to know how much water is actually being used.
• Be careful when using heating units as some will hurt or kill your plants. Ventilation is really important. Allow enough air in to aid in combustion. Outside vented heating units are best. If you must use a portable unit, it is best to not let it run all night. I will usually run the unit for a short period, and then wait a few hours before starting it up again.
• Double walled units require a blower to inflate the two layers of plastic. These offer better structural support, but require some power to run the fan. Unless you can come up with solution to this you might be best going with only one layer.
• Don’t forget that pollination is necessary for many crops. Each farm will have different solutions and different problems. Hand pollination works great on tomatoes in the early stages while it is still cold outside. Once the sides are up and the bugs are out, nature takes over. Blowers work also. Some farmers ship in bees. I have had no problem because I grow chemical free crops and have an abundance of insects on the farm.
• A trick I use to counter many diseases is 35% hydrogen peroxide. I use 1 part peroxide and 200 parts water. Spraying the plants with this keeps most diseases in check. For disease outbreaks, I mix 1 part peroxide to 100 parts water. (Don’t get the concentrated stuff on your hands!!) This will also disinfect as well.
• Copper Bordeaux is also a fairly safe solution for fungus diseases, but is more expensive and the copper levels can build up in the soil.
• We lay the plastic mulch by hand in the tunnel and it works just fine.
• When you buy drip tape, be sure to get some splices, as mice tend to cause occasional leaks. Even with a tank on a trailer, you will need a filter and a pressure regulator. These are inexpensive and are available at Jordan Seeds.
• Remember to use the roll up sides as more than frost protection. We use them to regulate the growing temperatures at night as well. They also work great to keep out raccoons at night and early morning and late night turkey attacks.
• While this next suggestion will not be a solution for some, it works well. We have a $5 transmitter radio and two sets of rechargeable batteries. We play the radio in the tunnels to discourage animals. A good conservative talk radio show works the best! No country and western!!!
• Before you put up your tunnels, work the soil and design the outer edges so that water drains away from the tunnels. I used a back blade on the last one I put up. Sure wish I had thought of it when I put up the first ones.
• I use 2 x 4s along the sides before I put on the wobble wire tracks. I strongly recommend this. (Treated lumber should be used.)

Other crops grown in high tunnels:
Tomatoes. We were able to harvest about 20 lbs of tomatoes per plant using a determinate beefsteak variety. The tomato plants in the tunnel gave us a very clean, large, crack free tomato. Flavor was excellent and the tomatoes seemed to have higher sugar content. Because the plants were kept dry, we noticed no disease problems. Watering was done through drip tape laid under the plastic mulch. (Drip tape is an excellent method of watering if you do not have running water available. The tape requires very little pressure and thus can be gravity fed by a water tank hauled to the site on a trailer) I strongly recommend plastic mulch in a tunnel, as this reduces evaporation and allows for less stress on the plants. Caution should be made to not plant tomato plants too close together as this could bring about disease and pest problems. We try to keep plants between 18 inches to 24 inches apart in rows that are 4 feet apart.

Cucumbers. Cucumbers are a great crop in the tunnels and the flavor is great. Use varieties that do not require pollination. Be sure to supply some sort of support for the vines to climb on. Water must be supplied consistently to maintain quality cucumbers.

Peppers. I believe peppers are the most trouble free vegetables in the high tunnel, Yields are exceptional. Be careful to keep moisture even throughout the season and don’t water too heavily at one time. Keep in mind, if you leave the peppers to turn red, you will substantially limit production. Also consider pruning off deformed, blemished peppers as soon as you see them. Why weaken the plant with valueless produce?

I was assisted in this project by my family, neighbors, friends, Tim Connell from the University Extension in Stevens Point, Midwest Bio Ag, MOSA and MOSES.


• Using the tunnel drastically reduced the work load by extending the growing season supplying a longer window to accomplish the needed work.
• Due to the protection from the elements I was not delayed by the weather and was thus able to keep on top of the weeds.
• Disease, which is usually caused by weather extremes, was eliminated.
• It was easier to deal with the pest and weather concerns because of the tunnels.
• Because crops ripened earlier I was able to command the highest prices and had virtually no competition at the market.
• The tunnels eliminated much of the normal problems with crops and thus gave the highest yields and best quality.

• During high winds one is usually concerned about possible damage to the structures.
• Caution must be used to make sure the sides are raised prior to the sun baking the plants. A little neglect could wipe out your crop.

• We were blessed with a number of articles in the local papers.
• The Country Today, a state farm paper, had an article regarding the high tunnels.
• Our field day generated a large crowd of over 65 people
• I was able to offer a presentation to three local produce auction sites and their growers thanks to the University Extension
o These growers were very receptive and showed strong interest in the future of using High Tunnels in their farming practices.
• The Upper Midwest Organic Farming Conference offered me the opportunity to hold two classes throughout the conference.
• We have put up a web site presenting the High Tunnels along with the results of our grant project.
• We also have had numerous calls and visits from people interested in High Tunnels.

Response has been extremely positive and quite a few individuals already have put up high tunnels because of this project. Those who have already put up tunnels are market growers, master gardeners, and those who are incorporating the tunnels into their own private gardening practices. About 70% of the respondents at the three auction sites stated that they intend to put up a high tunnel. We have been extremely pleased with the results of the outreach.

I am appreciative of the SARE program and the opportunity it offered me through this grant. The benefits to others and myself have been beyond expectations. I would encourage you to continue to award grants to those who are seeking new ways to enhance sustainability for the small farmer.


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.