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Hortikultur – højkvalitets produktion af roser i drivhuse

The South African company Morgan Roses, was founded in 1996, just outside the town of Warmbaths. Initially, it had naturally ventilated greenhouses covering an area of one hectare. The company has now expanded to encompass 4.5 hectares, producing about six million roses a year. Morgan Roses sells to the local market and exports to international markets, i.e. Western Europe, Eastern Europe, and the Middle East. During 2001, the average price for roses on the South African market was ZAR*) 0.72 each, while the average export price per rose amounted to ZAR 1.40. It would obviously be of great advantage for Morgan Roses if they were able to export a large percentage of their roses. The only thing keeping them from doing so was the difficulty in growing sufficient high quality roses to meet the quality standards and continuity of supply demanded by the export market. At the time, only about 40% of their roses met these standards.

Roses are graded according to stem length and bud size. Generally speaking, the market demand is for long-stem roses. In Eastern Europe, there is also a great demand for big buds (i.e. larger than 5 cm). The roses produced by Morgan Roses had, on average, stem lengths measuring 50 to 60 cm and never longer than 70 cm with buds sizes ranging from 3.5 to 4.5 cm. Although these were acceptable quality roses, they were by no means top quality. Export roses are priced according to stem length, averaging ZAR 0.023 per cm. Producing roses that are 10 cm longer would therefore result in an additional income of ZAR 0.23 per rose. If, at the same time, the bud size could be increased, then the roses would naturally appeal to a much larger market segment.

Controlled climate – key to the success

The root of the company’s problem lay in maintaining the climate in it’s naturally ventilated greenhouses close to the ideal conditions for roses. An ideal climate for roses is 27°C with a relative humidity (RH) of 60-70%. The Warmbaths region, during the summer months, has a mean maximum temperature of 34.7°C, with a mid-day RH of 45%. These outdoor conditions make it impossible to increase production and achieve quality roses. To compound their problems, the climate conditions inside the naturally ventilated greenhouses were hardly better. The temperature frequently rose to 34°C, and the fogging system in the greenhouses was incapable of raising the RH above 50% without wetting the roses. This brought about excessive stress for the rose plants, resulting in short stems and small buds. Furthermore, the roses that were grown during the summertime produced what is known as “hollow buds”.

Cool solution

In order to alleviate the problem, Morgan Roses approached Munters for assistance in designing their new 3,200- sq.-meter greenhouse. To enable them to provide a greenhouse climate close to the ideal for roses (27°C, 60-70% RH), Munters recommended installation of the CELdek system. Plants were subsequently transplanted from the existing naturally ventilated greenhouses to the new greenhouse with CELdek system. The outcome was simply astonishing. The Bianca cultivar plants had produced roses with an average stem length of 60-70 cm, with 80 cm not being uncommon. The bud size increased to five cm on average. Even more impressive was the fact that nearly all the roses produced in the new greenhouse were of export quality.

Hurtige fakta

  • Reduce the temperature inside the greenhouse by 7°C
  • Remove moisture and reduce humidity during night time
  • Achieve high quality and appearance roses even through knuckle cutting
  • Improve the control of the house environment, and limit the temperature and humidity extremes
  • Eliminate the occurrence of powdery mildew and red-spider mite
  • Reduce power consumption
  • Guarantee maximum profit

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