organic agriculture

The Midwest Organic
& Sustainable
Education Service
PO Box 339,
Spring Valley, WI
54767
715-772-3153
info@mosesorganic.org
www.mosesorganic.org

"This institution is an equal opportunity provider"

" Our mission is to help agriculture make the transition to a sustainable organic system of farming that is ecologically sound, economically viable, and socially just, through information, education, research, and integrating the broader community into this effort."

subscribe to the Organic Broadcaster:
One year (six issues) $20. Two years (twelve issues) $38
return to archive list
MOSES Homepage

The Unfrozen Tundra: Extending the Growing Season in Green Bay
By Bill Wright

During the winter of 2002/2003 I read Eliott Coleman's book Four Season Harvest, and became aware of several growers in southern Wisconsin who were using high tunnels for season extension. This intrigued me, but the winter climate in Green Bay, Wisconsin is different than Madison or coastal Maine. In January 2004 the average high temperature for Green Bay was 20 degrees, and the average low 4 degrees. During that month we had 11 nights of below zero temperatures, with the bottom dropping out at -14 degrees. We also frequently see cold temperatures fairly early in the season, as was the case in November of 2003 when the temp. dipped to 11 degrees on November 8th and 13 degrees on November 9th. Not exactly ideal growing conditions for tender green things.

I decided to give it a try, however, and with financial assistance from UW-Extension Northeast District Fund for Innovative Programs, and space provided by Green Bay Botanical Garden, constructed a 12'x 44' high tunnel in the summer of 2003.

In planning I felt it important to impose some restrictions on the project so that the system being trialed would be strongly appealing to growers in our area . First, I decided to not use any supplemental heat, thus eliminating the extra expense of heaters and fossil fuel. I did not want to use any electricity; therefore ventilation would need to be accomplished without electric fans. This would give the grower more flexibility in placement of a high tunnel. A system that required minimum human intervention was needed since we were not going to be there on a daily basis to monitor the tunnel. Likewise, many growers have off-farm jobs and are not able to constantly monitor conditions. Also, being unsure if the concept would work, I did not want to invest a large amount of money and decided to design and build the tunnel myself. From the grower's standpoint, this would also help to maximize the return on investment.

With the assistance of a summer intern, the site was first leveled and the four corners of the structure were marked, making sure everything was square. We used ¾"x 30" black pipe driven 24" into the ground for our anchor posts. The corner posts were set first, and then using a string stretched between the outside corner posts to keep all posts perfectly aligned, we set the ground posts at 4' intervals. I highly recommend having two people for this operation; one to hold the pipe and one to swing the sledgehammer, since you need to drive the anchor post straight into the ground. We used a level to check our progress when half of the post was in. A large machine bolt placed in the end of the pipe can protect the end of the pipe from being smashed, since a smashed pipe can make attachment of the ribs very difficult.

We bolted 2"x 6" cedar boards to the anchor posts to form a kickboard. While treated lumber is less expensive, we chose not to use it because of the direct contact with the soil and restrictions for use in organic systems. A small trench was dug around the outside of the kickboard and using 8" wide flashing, a varmint guard was placed on the bottom of the kick board. The thought was to keep voles from tunneling under the kickboard. However, it didn't work as planned.

Our rib design was a gothic arch with a 4' sidewall. In order to create a form to bend the ribs, we hammered pipes into the ground at the ends and corners of the pattern. We used this form to bend 5/8" rebar to the desired shape (3-10' pieces were joined together with ends overlapped 3' to form the 24' pieces we needed for the rib). We then covered the rebar with 23' pieces of 1 1/2" plastic irrigation pipe so that there would not be any abrasion on the poly cover. We also installed 3 purlins using PVC pipe. While these ribs were economical, they were too flexible and after 2 years the structure shows obvious signs of wear. I will purchase a commercial structure for our next project. I think the extra cost is well worth the investment.

The end walls were framed using 2 x 4's just as you would frame a wall in a house. Each end wall had a door with a vent window near the peak. The south end wall and the door were covered with the same poly material used to cover the structure. The north end wall was covered with used wet felt from a paper machine. This material was free and held up well even when exposed to the elements.

The poly cover used was standard, 6 mil, 4-year green house poly. The poly was fastened to the kickboard by "sandwiching" the edge between lathe strips and then screwing the lathe/poly sandwich to the kickboard. We started early one morning to apply the poly cover but it seemed that as soon as we unrolled the plastic a breeze appeared. Since there were only two of us to handle this 48'x 24' sheet of poly, which acted like a sail with the slightest breeze, we started by fastening the plastic to the west side of the structure. We then used tennis balls to fasten 25-foot ropes at 8' intervals to the other side of the poly. We would then start at the north end, throw the first rope over the top and pull the poly as far as possible. We then tied this rope off at the base and repeated the steps with each rope until we reached the south end of the tunnel. We then went back to the first rope at the north end and repeated the process until the poly was in place. While I was pulling the ropes, my helper was inside the tunnel with a broom to help the rope and poly over the purlins. The plastic was then fastened to the kickboard on the east side in the same manner as described earlier.

We achieved our "automatic" ventilation by using a product called Univent, which we were very pleased with (though, in my role as Extension Agent I want to be careful to not endorse any product or manufacturer). This unit consists of a wax- filled cylinder with a metal rod. When the wax inside the cylinder heats up, it expands, forcing the rod forward and opening the vent. When the wax cools, the rod can retreat and the window is closed by a spring. (The manufacturer recommends that the wax cylinder not be left outdoors during extremely cold weather.) In our next high tunnel, the only change we will make to this set-up is to have larger vents. This system has allowed excess heat to escape from the high tunnel without the necessity of being present on a daily basis to open or close doors or to roll up sides.

Trials
During the two years our high tunnel has been in operation, we have conducted a variety of trials. Some have been successful, some have been labeled "learning experiences." Here is a brief rundown of the items we have planted and results we have seen in the unheated high tunnel.

Fall Salad Greens
We planted a variety of greens including spinach, lettuce, mustard, etc. and have had our greatest success with these greens in the fall of the year. We used #9 galvanized wire to form loops over the beds. These hoops were used to hold floating row covers above the crops so that the row cover and the greens would not come into contact and freeze together. With this set up we have successfully grown salad greens into January each year. We are still experimenting with planting times for late season harvest. In our region, the amount of available daylight diminishes rapidly throughout October and drops below 10 hours per day in early November. At this low light level, plants begin to go into a dormant state. Therefore, planting times must take this into account so that plants are not too mature (I'm not sure I understand what this phrase means) or fail to grow properly.

Fall Root Crops
Carrots and beets were planted in the fall of 2003 and did well (the carrots were not planted until September 1 and should have been planted earlier). The soil within two feet of the sidewall froze but in the center of the high tunnel only the top inch or two of soil froze and only for three weeks in late January and early February. Therefore, the high tunnel acted as a "living root cellar" and allowed for carrots and beets to be harvested throughout the winter.

Spring Salad Greens
After our success in the fall of 2003 with salad greens, I thought spring greens would be easy. However, I soon discovered that the opposite was true. The first problem was the wildly fluctuating temperatures. Daytime temperatures would climb to 100º or more on sunny days and the upper layer of soil would quickly dry out. Since we had direct seeded our greens, this lead to poor germination. (Of course, if we would have been on site on a daily basis we could have avoided this problem). The next problem we encountered was voles. Voles are vegetarians and really enjoyed the tasty greens. We tried to trap them but had little success. We later experienced aphids and attacked them with an insecticidal soap solution. We did manage to grow spring greens; however, it required a lot more effort than the fall greens.

Strawberries
We planted 48 Chandler strawberry plugs in September of 2003 and picked our first berry on May 6, 2004. That is about 6 weeks earlier than berries grown outdoors. We picked 35 quarts of berries over the next 5½ weeks. The berries had an outstanding flavor, were firm, and the centers were not hollow. Once in blossom, we covered the berries with floating row cover whenever temperatures in the low 30's were predicted. We pollinated the blossoms with a small artist's brush since we did not have any natural pollinators available during April. Lack of pollinators would seem to be the biggest problem facing growers and purchased bumblebees may be one solution. I have read of leaf blowers being used to move the pollen around but have never tried this myself.

Russian Fingerling Potatoes
We planted one pound of Russian Fingerling seed potatoes in April 2004. The emerging potato plants were not covered by floating row cover, and one night, with temperatures in the 20's, the emerging plants froze. (Only the portion above the ground froze). The plants recovered and we later harvested 43.74 pounds of fingerlings from that one-pound of seed potatoes. I checked with the dealer from whom we purchased the seed and he stated that under good growing conditions, we should expect up to 20 pounds from one pound of seed potatoes. We certainly exceeded our expectations on this one!

Sugar Baby Watermelon
We direct seeded Sugar Baby watermelons in May but faced several problems. First, under the warm conditions of the high tunnel the plants produced additional and longer vines than I had ever seen on watermelon in our area. This created very crowded conditions and when combined with the fact that we did not have roll up sides, led to powdery mildew problems and dying vines. I still believe that the high tunnel is an excellent place to grow watermelons and plan to try them again with greater spacing and more ventilation.

Heirloom Tomatoes
We transplanted striped German and Nebraska Wedding tomatoes in late May (after danger of frost) both inside the tunnel and outside. The tomatoes inside were watered with a soaker hose and showed no sign of disease. The yields inside and outside during most of the season were comparable, but the total yields for those inside the high tunnel were greater since the plants escaped the early frost and were able to produce for a few more weeks.

Asparagus Beans
Asparagus (or yard long) beans are native to Southeast Asia and are one of my favorite beans. We planted a ten-foot row and set up a trellis. Under the warm conditions the vines climbed up, over the trellis, then kept on growing. We harvested 15 pounds of 12-14" beans from that single row. Other than the problems with all of the vines, these beans could create a shading issue for vegetables in the immediate vicinity.

Bitter Melon
This is another Southeast Asian vegetable that we planted but did not trellis. The vines soon overtook the floor area. We did not weigh the fruits, but the plants produced a large quantity of bitter melons.

Early Tomatoes
On April 15, 2005 we started transplanting tomatoes into the high tunnel. We used Early Girl and Stupice and found that Stupice withstood the cold much better than the Early Girl. The plants were covered with floating row covers since 10 of the last 15 nights in April saw outside temperatures in the low 30's. The Early Girl's did not die, but turned a gray-green color and growth was stunted. We picked our first tomato on June 9th and full production kicked in around July 1. The tomatoes continued to produce abundantly throughout July and August.

Sweet Potatoes
We planted sweet potato slips and the vines spread rapidly. The only problem we experienced was that the grasshoppers quickly chewed off all young leaves. A layer of floating row cover solved that problem.

Jicama
We planted jicama in the spring of 2005 and as of this time (October 2005) the plants are still climbing the ribs of the tunnel. I'll be anxious to see the size once the roots are harvested.

As you can see, the high tunnel has worked well in Green Bay, even with the self imposed restrictions mentioned earlier. We will continue to conduct trials in our present unit and would welcome any suggestions for future trials. Our next major project is to erect a large high tunnel in cooperation with Green Bay Area Public School Food Service Department. This high tunnel will be used for gardening and nutrition education each month of the school year except January and February. This will be an exciting adaptation for utilizing a high tunnel in Wisconsin.

I would also like to experiment with peach trees in a high tunnel. There are many varieties of peaches that are only hardy to zone 6 that have outstanding flavor when tree ripened. If you bite into a tree ripened Sun High peach like you would an apple, the sweet, warm juice will run down your wrist. There is nothing like this available in Wisconsin and we need to bring this experience to our customers. If anyone has tried to grow zone 6 peach varieties in a high tunnel in the upper Midwest, or know of anyone who has, please let me know. I have some ideas about how to trial this concept and would enjoy comparing notes with others.

Bill Wright is Community Garden Coordinator for Brown County UW-Extension. He can be contacted at mailto:bwright@itol.com