Evaluation of Raspberries Grown in High Tunnels for a Northern Climate

Final Report for FNC04-529

Project Type: Farmer/Rancher
Funds awarded in 2004: $6,000.00
Projected End Date: 12/31/2004
Matching Non-Federal Funds: $6,000.00
Grant Recipient: Duluth Farmer's Market
Region: North Central
State: Minnesota
Project Coordinator:
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Project Information


Lois Hoffbauer of Duluth recently received a grant to experiment with using a greenhouse-like high tunnel to provide Duluth customers a longer raspberry season. Her research could also create a new tool for sustainable agriculture in Minnesota and in other cold climates throughout the country.

Raspberries are a high-value product in Duluth, where the Zone 3 short growing season makes visitors to the farmer’s market hungry for every bit of summer sweetness they can find. Talking about her experience with farming, Hoffbauer explained, “We learned years ago that, living this close to Lake Superior, we had to ‘cheat’ the weather any way that we could.” The high tunnel would extend the season on both ends, allowing her to produce raspberries earlier in the year and to experiment with fall-bearing raspberries.

While tunnels like these have been used for annual crops, this is the first time they will be used for a perennial plant in Minnesota. Hoffbauer heard about Penn State’s experimental use of perennials under tunnels and wants to see how it will work in Minnesota: “I don’t know of anyone except Penn State that has had perennial crops under plastic. It will change the entire way that the plants live because the sun will heat up the ground even in the winter, then freeze again when the sun goes down.” Hoffbauer will compare high tunnel yields to yields of raspberries not under the tunnel.

The new greenhouse will be up by the end of October. In the summer, field days will provide visitors a close-up look of the tunnels.

Hoffbauer has been farming in Duluth for over 25 years. She and her husband have 12 acres of sustainably produced vegetables, fruits, and free-range chickens, and 50 acres of Christmas trees.


Project Background

Our farm consists of 12 acres if sustainably grown vegetables and fruits, free range chickens and 20 acres of Christmas trees. We use sustainable methods and Integrated Pest Management to work our farm. We use black plastic mulch for our tomatoes, peppers and pumpkins. Between the rows of tomatoes and peppers, we mulch with weed-free straw. We cover the tomatoes/peppers with a floating row cover got early season frost protection. On our corn crop we plant 10 varieties with various lengths of ripening. We use a 300 foot piece of floating row cover that goes over 12 rows at a time and as the corn grows, we move the cover up the field over successive rows. We have had tomatoes under high tunnel production for over 15 years. We already have our peers interested in out methods and adding another high tunnel would just add one more dimension.

Project Objectives:

To provide fresh raspberries to customers in an extended fall season and enhance farm income, the project will evaluate the feasibility of utilizing a 96' x 30' hoophouse.


Materials and methods:


Due to the northern location of our farm, and shortness of out growing season, we use some season extenders to allow us to be at our local Farmers Market earlier in the year with high value products. Season extenders also give frost protection in the fall giving us a longer growing season. Raspberries are a high value crop and by using a high tunnel, the season will be longer at both ends.

Since receiving this grant we have done a lot of research on High Tunnel production. While at the Minnesota Fruit and Vegetable Conference this year, we attended sessions on High Tunnel production. Our ideas changed slightly regarding the production methods. Once the High Tunnel was constructed, we brought in truck loads of mulch and tilled it in the top soil. We then raked the topsoil/mulch mixture into a raised bed. We put trickle tape under each raised bed for irrigation. Instead of using canola for weed prevention, we went with black landscape fabric. Because the fabric ravels, we used a blow torch to cut hole in the fabric, then placed each plant in a hole. The plants had been in another greenhouse in 1 gallon pots, so most were already leafing out. Each day, I can see them getting greener. They will not be in full production until August, 2005.

We are going to be trailing 6 different fall bearing varieties. We have Polona, Fall Gold, Autumn Britton, Josephine, Autumn Bliss and Summit. We have extra plants, so that if by chance some die, we will be able to replace them this year. I believe the trick is going to be to keep them alive this winter. We are going to mulch them heavy and then take the mulch out next spring.

We have documented the entire process with pictures. At our field day, we will have those on display so that people can see what this process entailed. Friends, neighbors, and peers are very interested in what we are doing. Some of them have been in on “the ground floor”. They are always surprised as to daily progress. My husband teaches a weekly gardening class at our local Indian Reservation, and they are going to be the first to come out and see it in production.

I believe this project will help to revitalize small farms in out area by giving idea on how to “cheat the weather”.

Bob Olen- Extension Educator and Paul Otten who is probably the biggest raspberry producer in Minnesota have given valuable input. We speak to Bob on at least a weekly basis to keep him informed on the progress. Paul will be coming to the field day to see the results. Many local businesses have provided services and they will be recognized at the field day.

So far the results are as we expected. The plants are in the ground, they are irrigated every 2-3 days. They are leafing out and getting greener every day. The only comparison I have is to the one acre summer bearing raspberries that have been in full production for 20 years. So far the summer bearing plants ahead of the plants in the high tunnel, but that is to be expected. By mid summer, we will be able to see the real results.

We learned that this was a lot more work than we expected. We got behind last year because of the wet fall, and so the construction could not begin until spring. I would recommend that in the future, the construction should be completed in the fall and ready to go for spring planting.

Research results and discussion:

The impact for us will be the extra dollars brought in to our family from the sale of raspberries. It will also impact those that I hire, because they will have to spend. I’m also looking to be able to meet the demands of a local jam maker, and wine maker, hoping to be able to market the products that way, also.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

I am having a field day on August 14, 2005. I will be inviting local media, the local businesses that provided services, the vendors at the farmers market, and open to everyone in the community. I will be advertising in the SFA newsletter and local newspaper. I plan to have an outline of the project, a picture gallery, sampling data, and economic data. I plan to keep updating the public, and I hop to lead one of the sessions on high tunnel production next year at the Minnesota Fruit and Vegetable Conference.


This has been a great opportunity for me to try something fun. It was more work than we anticipated, but I think that in the end we will be pleased with the results.

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.