Slowing down ripening during periods of heat benefits the strawberry’s fruit quality 

The hot summers and heatwaves early in the year are causing growers to take a new look at available options for controlling light and heat in their greenhouses. The strawberry company Cevefresa in Wiekevorst near Heist-op-den-Berg in Belgium has four cooling options at its disposal: ventilating, using a moveable screen, coating and sprinkling the roof. ‘We cannot really make use of the sprinkling option very often,’ says owner Patrick Celis. ‘The groundwater here contains so much iron that removing it is difficult at best. This creates deposits that make the glass less transparent and that are very difficult, if at all, to remove.’ 

In order to have sufficient water during dry periods, he has therefore constructed a relatively large 8,000 m2 basin for his greenhouse. He generally uses the captured rainwater as irrigation water and only in extreme cases for sprinkling the roof. 

The gutter height of the greenhouse is 3.5 metres. The greenhouse contains a translucent energy screen. ‘We can use this screen to reflect the sunlight, but because the greenhouse is relatively low, it regularly becomes too warm below this moveable screen,’ he says. 

Tasty Varieties 

Cevefresa grows the tasty varieties Sonata and Sonsation in spring and the standard variety Elsanta in summer. ‘The early varieties are more sensitive to heat. The harvest starts at the beginning of April and lasts until mid-May. We have regularly had high temperatures during this period in recent years. This adversely affects the quality. While pollination remains good, the period of fruit growth and ripening becomes too short, resulting in small fruits.’ 

The question then is, what is the best strategy: selectively focus on keeping just the heat out of the greenhouse, or partially block the sunlight. ‘To find the answer to this question, we had half of the greenhouse coated with ReduHeat and the other half with ReduSol,’ he says. 

ReduHeat allows the growing light (PAR) to pass through, but blocks infrared, which heats the crop. ReduSol reflects more of the growing light, as well as the infrared light. 

Better Quality

‘The trial showed that ReduHeat did not work fully satisfactorily. We asked contractor De Ceuster to apply a few additional buckets, but that also made it more expensive. The conclusion is that in spite of the fact that it removes a lot of light, ReduSol is the best solution in our situation, because it also removes more heat. It is a consideration in which you must include all of the pros and cons,’ says Celis. 

Under ReduSol the greenhouse temperature was considerably lower in comparison to ReduHeat, which results in a better fruit size. Cevefresa in part sells the strawberries through the Coöperatie Hoogstraten auction house, as well as in large part to consumers through well-visited strawberry vending machines where clients can serve themselves from March to the end to the year. ‘That went exceptionally well this past year. While we have seen a lot of greenhouse expansion in recent years, prices are staying reasonably stable. In addition, healthy products appear to have caught on more during the corona year.’