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BLN trial

Cultivation of organic vegetables in Winter - Lettuce and Cucumbers from polytunnels

Organic vegetables and organic milk are the two most important organic food groups for retailers in Germany. Through this, regional production is gaining importance. More than three quarters of consumers say they prefer regional products. But in winter, many businesses are having a hard time providing a broad range of organic vegetables. Often the domestic supplies are limited to winterproof specialty varieties such as lamb's lettuce and arugula. Other varieties are usually produced in greenhouses, which is not very profitable due to energy inefficiency and frowned upon for ecological reasons. In a trial conducted by the Bundesprogramm kologischer Landbau und andere Formen nachhaltiger Landwirtschaft (BLN, eng. federal organic farming programme) and the Chamber of Agriculture North Rhine-Westphalia, alternatives for vegetable production in winter were tested. The trial was centered around the production of fresh vegetables in unheated foil tunnels. 

The cultivation of various cold tolerant salads in winter turned out to be profitable in the polytunnels. Image: Chamber of Agriculture North Rhine-Westphalia.

The alternative range was tested especially for organic farms, as well as salad mixes with Pak Choi, chard, red beets, Winterpostelein and plantain. To optimize the system of polytunnels and make it more profitable, the cultivation of country cucumbers was tested in the tunnels during the summer.

Good returns for lettuce
In all three years of the trial, the cultivation of salads was unproblematic under trial-conditions as well as in practice. Especially postelein turned out to be a good option due to high cold resistance and the production of mass. The labour was a little higher compared to lamb's lettuce. Early planting during fall was important for the yields, so young plants were able to develop enough roots. Harvest was between October and April. As expected, there was a decrease of yields between the beginning of December and early March in all three years. Long periods of frost clearly reduced the yields. Highest yields were reported in October and March. On average, 400 to 500 grams of salad were cut per square meter, two to four times per plant. There were no problems with mildew. 

Cucumber cultivation improves profitability
During the two years of studies for the cultivation of country cucumbers in the foil tunnels in summer, the yields were significantly higher when raised with wire and string compared to soil cultures. According to experts this is due to fewer cases of mildew. Furthermore, the raised cucumbers had a more uniformly colored skin, which makes them easier to sell.

The economical evaluation showed that the production of different lettuces in polytunnels was profitable. The additional cultivation of cucumbers during the summertime further improved the profitability of the system. The contribution margin of the salad mixes were 10.28 per square meter on average. The cucumbers reached 7.70 per square meter. With an overall marginal return of 17.98 per square meter, the "Polytunnel in Winter" clearly outperformed the margin of a heated lettuce winter variety, which is below six Euro.

Successful tasting of the salad mixes
To gauge the potential of the salad mixes with consumers a tasting with and a subsequent survey were included in the trial. Generally, the salads were well received, especially the loose produce. With some additional information for the sustainable cultivation of the salad mixes and periodic tastings, the sales could be further increased according to the research team.

Source: oekolandbau.de

Publication date: 8/14/2017


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