Many green pot plants are grown with little direct sunlight. Reason for this is the origin of the plants: they live on the bottom of a rainforest. But what happens with the production and quality when a grower does allow more light in the greenhouse? De Business Unit Glastuinbouw van Wageningen University & Research discovered that one tropical plants can handle it better than the other.
For the study several varieties of two types of green plants were studied during the summer and autumn: Dracaena and Calathea. The plants were grown in two different departments with diffuse glass at the test location in Bleiswijk. In one department sun screens are being used to prevent an excess of sunlight. In the other department the plants received 80 percent more sunlight for 5 months.
The Calathea handled better than the Dracaena. The Calathea produced 20 percent more leaf crop. Good news for growers of this crop: by the screens not that often production rises. Growers can thus shorten their growing cycle and thereby grow more plants per year. But the percentage of 20 percent indicates that the plant sometimes had to deal with stress. Otherwise, production would have increased by a maximum of 80 percent. After all, in other crops - such as tomatoes - the principle is '1 percent light equals 1 percent production'.
Stress indicates that the plant can not convert the sunlight into photosynthesis, and therefore can not convert more CO2 from the air into sugars. The surplus of light is therefore converted into heat and into light with other wavelengths (fluorescence). During the research fluorescence has been measured at various times to determine when stress occurs. This acquired knowledge provides tools for improving the cultivation of photosensitive pot plants.
The Dracaena type is susceptible to stress. More sunlight in this plant hardly causes a higher production. The quality had to suffer: the leaves of the plant yellowed. By temporarily giving these plants less light, these effects could be nullified again, making the damage happily reversible.
Club of 100
The research into the influence of light on green pot plants has been funded by the Club van 100, a collaboration between supply companies in greenhouse horticulture, initiated by WUR Greenhouse Horticulture.