Organic Strawberry Production: Extending the Season with Low Tunnels

Final Report for FS08-224

Project Type: Farmer/Rancher
Funds awarded in 2008: $10,000.00
Projected End Date: 12/31/2011
Region: Southern
State: Alabama
Principal Investigator:
Carol Garrett
Auburn University
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Project Information


This project was designed as a demonstration project to determine if the strawberry harvest season could be extended by simultaneously employing four different production methods and growing three different varieties designed to spread out production and harvest over a longer period of time.

The treatments were:
Treatment 1 Bare ground, no low tunnel
Treatment 2 Bare ground, low tunnel
Treatment 3 Black plastic, no low tunnel
Treatment 4 Black plastic, low tunnel

The 3 strawberry varieties planted were:
1. Allstar
2. Camarosa
3. Chandler

Black plastic mulch produced berries 1-2 weeks earlier than the matted row system; plants on black plastic mulch with a low tunnel produced berries about 1 week earlier than those on black plastic mulch without a low tunnel. In the matted row system the low tunnel produced a greater number of berries earlier than without the low tunnel, but the total number of berries produced was greater without the low tunnel in both the black plastic mulch system and in the matted row system. The matted row system produced more berries than the black plastic mulch system, but reguired more labor picking and weeding.

Chandler produced the most amount of fruit, followed by Camarosa, and Allstar produced the least amount. Camarosa consistently produced a superior high quality berry; large, well shaped, very tasty, and fewer diseased berries.


Organic farmers need to maximize profits with high-value locally produced fruits and vegetables. Strawberries are a high value crop, especially if they can be advertised as being locally grown and pesticide-free. Farmers who can get their strawberries to the market early can obtain premium prices for them. Strawberries from Florida are available early in the year, but they are not harvested ripe and are not pesticide-free. Low tunnels provide an opportunity for local organic growers to economically produce early berries. Growing strawberries in a greenhouse or high tunnel requires a large monetary investment, which is not practical for the small-scale, beginning, or limited resource farmer. Low tunnel strawberry production, however, could help farmers increase their profit margin and enhance their economic sustainability.

Project Objectives:

1. Investigate the profit potential of early strawberry production using low tunnels.
2. Compare the performance of 3 different strawberry varieties in the traditional matted row system and plasticulture under low tunnels and organic production methods.
3. Design economical and functional low tunnels that would be adapted by limited resource farmers.

Low tunnel strawberry production would be an affordable production method that would allow local farmers to harvest earlier and obtain premium prices for their product. Farmers would obtain many of the same benefits as they would with unheated greenhouse production, yet they would have less production expense. Low tunnels, unlike high tunnels and greenhouses, can be easily moved around to permit crop rotation for pest control. Low tunnels are also an economical way to protect the crop from herbivore pests, such as rabbits and deer. Locally grown foods produced with low tunnels would be a more sustainable practice than importing these items from other areas of the country. Most of the materials used for low tunnel construction can be re-used for multiple growing seasons.

Strawberry production has shifted away from the traditional matted row system and gone toward plasticulture due to weed and disease problems and increased yield with the latter method. However, plasticulture is a more expensive and labor intensive production method and involves some sustainability issues, i.e. disposal and use of petroleum products.

Strawberry variety trials in this area have not included organic growing methods. I would like to compare the performance of a few of the popular varieties under organic growing conditions and low tunnels. It is possible that the varieties that perform best under conventional production methods would be different from those that perform best in an organic system that depends on slow-release organic fertilizers and ecologically based pest control methods. In a sustainable organic system with a focus on local marketing, other plant characteristics besides yield and shelf life might assume high priority. Characteristics such as plant hardiness, competitiveness with weeds, and fruit taste might be more important in this system.

In order to become accepted and adopted on a large scale, low tunnels must be user friendly. They need to be inexpensive to construct, easy to manipulate, and the materials should last for multiple years. The sides will need to be opened during warm weather and additional coverage may be needed on very cold nights.

Spring 2008
Beds will be prepared for planting.
Strawberry plants will be planted in 6 of the new beds and mulched with hay.
The other 6 beds will be planted in a summer cover crop of cowpeas.

Summer 2008
The strawberry plants will be kept weeded, watered, and will be side-dressed with composted manure and worm castings.

Fall 2008
The plants will be thinned.
The 6 beds that were planted in cowpeas will be covered with black plastic, fertilized, and planted with the 3 varieties.

Winter 2009
The beds that will receive the low tunnels will be covered. The covering will be manipulated as the weather dictates.
Fruit will be harvested as produced and records will be kept on weight and dates of harvest.
Fruit will be sold in Auburn and Tuskegee.
Spring 2009
Harvest and fruit sales will continue.
Strawberry plants in the matted rows will be fertilized.
Summer 2009
Beds will be kept weeded and fertilized.

Fall 2009
Matted row beds will be renovated.
Plastic mulch beds will be rotated to different areas. New beds will be planted.
The results of the study will be presented at the Annual Organic Vegetable Production Conference.
A poster or a talk will be presented at the Deep South Fruit and Vegetable Growers Conference.

Winter 2010
Repeat of winter 2009, with management adaptations.

Spring 2010
Repeat of spring 2009
A field day will be held on the farm.
The final report will be submitted.
The results will be published in the Organic Vegetable Production e-newsletter.


Materials and methods:

The project was delayed for one year.
This project was designed as a demonstration project to determine if the strawberry harvest season could be extended by simultaneously employing four different production methods and growing three different varieties designed to spread out production and harvest over a longer period of time.
The treatments were:
Treatment 1 Bare ground, no low tunnel
Treatment 2 Bare ground, low tunnel
Treatment 3 Black plastic, no low tunnel
Treatment 4 Black plastic, low tunnel

The 3 strawberry varieties planted were:
1. Allstar
2. Camarosa
3. Chandler

Strawberries were grown with low tunnels and without in order to extend the harvest season. Three varieties were planted: Chandler, Allstar, and Camarosa. Each variety was planted in four different beds (not raised beds): two of them were planted with the matted row system, one to be covered with a low tunnel and the other not covered, and the other two beds of each variety were planted in plastic, similarly one was covered with a low tunnel and one not covered.

Below is a diagram of the layout. Each row is 4’ X 75’.

Treatment 1: Black plastic with low tunnel


Treatment 2: Black plastic without a low tunnel


Treatment 3: Bare ground without a low tunnel


Treatment 4: Bare ground with a low tunnel


The beds for treatments 3 and 4 (matted row) were prepared in the spring. They were planted with a single row of strawberries, 12-14” apart, in March 2009. Those beds were fertilized with compost and rotted sawdust and mulched with hay and pine straw. In the fall, the plants in the matted row beds were thinned and the daughter plants were planted in the rows for treatments 1 and 2 that had been covered with black plastic mulch. These rows had been planted in a summer crop of peas and beans in the spring and planted in strawberries the first week of October. These plants were planted in 2 rows with 12” between rows and between plants. All beds were fertilized with worm castings and watered with drip irrigation.

The low tunnels were applied in January. They were constructed of 9 gauge high tensile fence wire, cut into 7’ long pieces that were arched and stuck into the ground on either side of the bed. The wires were covered with a material called Dio-Betalon purchased from Peaceful Valley Farm Supply. It is superior to Agribon in that it is a more durable material, transparent, has some frost prevention and heat preserving features that Agribon lacks, and is not easily blown off by strong winds. The sides and ends of the low tunnels were held down with bricks. The wires and bricks were placed approximately every 2’. The low tunnels were removed after the last frost, which occurred around the mid April due to concerns about pollination and for ease of picking.

The strawberry plants were supplied with fertilizer in the drip irrigation system twice during the season. The first time Fertrell 4-1-1 liquid Plant Food from the Sea was used at the rate of 1 quart/5 gallons mixed supplied to the drip system with a siphon. The second application of liquid fertilizer was NatureSafe 8-5-5 pelleted fertilizer. A bag was placed in a pillow case and soaked in a barrel of water, which was used as liquid fertilizer.

Milky spore disease was applied to the growing and surrounding area Japanese beetle grubs, and beneficial nematodes were applied as well for immediate control. The only disease that was encountered was grey mold, especially in the matted rows due to the plants being too crowded.

Fresh fruit weights and numbers and harvest dates were recorded and notes made about the quality and size of the fruits.

The experiment was to be repeated the second year with modifications resulting from the first year. A time extension was requested and received, however, the time remaining in the project was not sufficient to accumulate data for a second year.

Research results and discussion:

Low Tunnels:
The treatments with the low tunnels produced slightly less fruit with both the black plastic mulch as well as with the matted row system.

Black Plastic Mulch vs. Matted Row:
The matted rows produced much more fruit than the plastic mulch, though the quality of the fruit was often not as good in the matted rows as on plastic. There were many more plants in the matted row systems than in the plastic mulch rows which accounted for the larger number of berries. The crowed plants also produced more culls.

Variety Comparisons:
Chandler produced the most amount of fruit, followed by Camarosa, and Allstar produced the least amount.

Chandler peaked in production a little sooner than Camarosa. Allstar peaked later in the season than the other two varieties.

Season Extension:
Treatment 3, which was the matted row without the low tunnel was considered the control treatment. The first berries were harvested from this treatment on April 20, but not until April 25th did this treatment produce at least 1 pound of berries (three pounds of berries were harvested on this date from treatment 3). Treatment 1 produced a pound of berries on April 14th and peaked at 3 pounds on April 20th, the greatest amount harvested on a single date for this treatment. Treatment 2 produced a pound of berries by April 17th and peaked April 28th with 4.6 pounds. Treatment 4 produced a pound of berries by April 22nd and peaked on May 7th with 43.75 pounds of berries.

Discussion of Results:
The rows planted to the matted row system contained many more plants than those planted in black plastic mulch, which accounted for the difference in yields between these systems. Though the matted row plants were thinned, they were not thinned to match the density of the rows in the plastic mulch. The crowded plants produced more culls than the plastic mulch, but also many more marketable berries. It was very time consuming searching for the berries, picking them, and discarding culls in the matted row system, but the yields were much greater. The matted rows also required a lot of weeding during the season. The plastic mulch treatments required new plants, but these were supplied by the matted rows.

Changes that I am making this coming season are:
1. I have replaced Allstar with Sweet Charlie
2. I planted Sweet Charlie in a hoop house in September for early production.
3. The plants in the matted row system are space further apart than last year.

So far, I have observed problems with grey mold in the hoop house due to high humidity and the fact that the plants were not mulched with plastic or straw. I have attempted to remedy these problems by opening up the hoop house daily to increase ventilation, and I have thinned the plants and mulched with pine straw to keep the berries off of the dirt.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Workshops were held on the farm during the spring of 2009 and 2010. The NRCS also came to the farm and observed the strawberry treatments, as well as a new hoop house treatment that was added in the fall of 2010. I conducted organic gardening classes on the farm in 2009 and in 2010 and we talked about the strawberry project and the students observed the plants. I had a couple of garden interns who also learned about the project.

Project Outcomes

Project outcomes:

Information was obtained on the benefits of using black plastic mulch and low tunnels in strawberry production. Also, the variety trials provided valuable information.

The results of this project show that strawberries can be harvested early by planting on black plastic mulch. Growers can get berries to market 1-2 weeks earlier than if planted on bare ground using the matted row system. However, the matted row system produced many more berries than the black plastic mulch. Another advantage of the black plastic mulch system is less labor is required for weeding than with the matted row system. By having a combination of these two treatments, a grower can extend the season, produce more berries, and have a source of plants for future plantings.

Low tunnels produced berries about 1 week earlier on black plastic mulch, but there was no advantage observed from using low tunnels in the matted row system. The low tunnels produced fewer berries than the treatments without them in both the black plastic mulch and in the matted row system. One factor may have been pollinator exclusion.


Potential Contributions

The results of this project will help growers to decide which strawberry production methods are most appropriate for their objectives and budget. Black plastic mulch and low tunnels are added expenses, but berries planted on plastic require less labor to maintain and the berries are of higher quality. The grower will have to determine if having berries at the market a week or two earlier can justify these added expenses. Matted rows require more labor to pick and weed, but provide a source of plants for future plantings. Low tunnels exclude pollinators, so they may need to be removed during the day when temperatures are warm enough.

Future Recommendations

I would recommend doing a replicated study of the comparisons of fruit production with black plastic mulch and the matted row system for organic strawberry production. I would also omit the Allstar variety and substitute a different one, such as Sweet Charlie. Since so many farmers have signed up for the NRCS Hoop House Grant, it would be helpful to determine the influence of hoop house production on season extension of strawberries. I think that the plants could be planted closer together to obtain more yield in the plastic mulch system, and red plastic mulch has been observed to increase yields over black plastic mulch. This season I placed the low tunnels on the rows in early December to see if that would produce earlier berries than last year when the tunnels were placed on the rows in Janurary.

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.