Effect of a diffuse glass greenhouse cover on rose production and quality

High energy use in rose cultivation at higher latitudes is caused by the need for artificial light to supplement scarce sun radiation. On the other hand, too high radiation levels are known to reduce flower quality. Therefore shading is widely applied during spring and summer, either through movable screens or seasonal whitewash. In both cases damage to the crop is avoided at the cost of reducing potential assimilation. Recent research on cucumber (Hemming et al., 2008a) has shown that diffusing cover materials improve the uniformity of vertical light distribution in a crop, therefore decreasing the energy load on the uppermost crop layer to the advantage of the underlying leaves avoiding light saturation in the upper leaves. These properties lead to an increase in production up to 10%. The application of such a cover on roses could decrease the need for shading so that a desired radiation sum could be achieved with less need for artificial light. Moreover, if the light distribution improvement on the crop leads to an increase in production, the same production could be achieved with less supplemental light, increasing the potential energy saving. Diffusion, however, usually implies a loss of overall transmission. This drawback can be avoided by antireflection coatings so that most recently diffusive glass covers have become available with the same transmission as standard glass. A rose crop (‘Red Naomi!’) was cultivated from August 2010 till September 2011 at the research station of Wageningen UR Greenhouse Horticulture in Bleiswijk in two compartments, one of them covered with diffuse, anti-reflection coated glass. This paper describes the effect of the diffusing cover on the photosynthetic properties of the crop, and the resulting production and quality