Green asparagus needs transparency
For the production of green asparagus, the use of plastic films meets different objectives to those of the production of white asparagus. In the case of green asparagus, only transparent films are used, as the spear needs light to produce chlorophyll (green) or anthocyanins (violet, purple). This film is placed on arches to create a tunnel where asparagus can grow. The precocious effect is sought by a warming of the soil that allows the plant to “wake up” earlier. For this, it is important to use a plastic with high thermal properties that will retain the calories at night which were stored during the day, as proposed by the company Europlastic. But the benefits of a plastic cover are elsewhere. The first step is to protect asparagus from the effects of climate, wind and rain, to improve its uprightness and visual appearance in order to obtain a premium quality.
Smoothing out temperature extremes
The plastic tunnel therefore acts as a mini-greenhouse. This protected area enjoys more moisture than the exterior air and is conducive to the quality of the asparagus. On the other hand, this small volume of air can quickly turn into an oven, reaching very high (or even too high) temperatures. In fact, in plots of green asparagus, films are usually removed in the morning and then replaced in the evening, which requires a lot of manipulation. To limit this labour time, film manufacturers offer a variety of solutions to avoid rising temperatures during the day. Europlastic offers a film which acts as a filter for short wave infrared radiation which is the source of the increase in temperatures. Daios uses the reflective power of ceramics added in a translucent film to reflect 30-40% of non-visible infrared rays. The aim of these films is to maintain the plastic cover for the duration of the crop by levelling out extremes in temperature. It is then possible to use harvest assistance machines in the same way as for green asparagus. The film is lifted and then replaced at harvest time, avoiding additional handling and reducing labour time. Another positive effect is that the tunnel becomes an enclosed space, which protects asparagus from diseases and pests, especially the asparagus beetle that has been on the rise in recent years.