Pay attention to generative or vegetative growth
Steering the crop towards vegetative or generative growth requires constant attention. Crop consultant Wim van Wingerden explains the possibilities.
How can you tell if a crop is developing generatively?
Wim van Wingerden: “The flowers are smaller and both flowering and cluster formation takes place higher up the plant. Additionally the flowers do not last as long. The stem at the top of the plant is thinner and the leaves at the top are smaller and the entire plant develops faster. It requires a lot of crop experience to be able to see these changes occurring.”
And what do you see in a vegetative crop?
“That's actually the opposite: the flowers are larger and both the flowers and clusters form lower in the plant. The flowers last longer. The stem below the top of the plant is thicker and the leaves at the top of the crop are larger. The whole plant develops slower.”
Wim van Wingerden
What is the effect of a coating?
“When a coating is used, we regularly see that the crop becomes more vegetative. This is mainly because the leaf temperature remains lower under a coating. The plant does not have to ‘work’ as hard. When using a coating it is important to measure the crop temperature. This can easily be up to four degrees lower than in a greenhouse without a coating. A thermal imaging camera gives a good insight into how crop temperature develops."
How do you steer a crop to become more generative?
“It depends on the approach by the grower, the type of crop and variety, the climate conditions and how generative or vegetative he wants to grow the crop. You can achieve a more generative crop by increasing the difference between day and night temperatures. With sufficient radiation the greenhouse temperature can be allowed to rise under the coating, so that the crop temperature also rises. If possible, the night temperature can be lowered. Both actions have the same effect: a larger difference between day and night temperatures.”
What role does the moisture balance play in this?
“To achieve a more generative crop the grower should avoid the absolute humidity in the greenhouse from becoming too high. If that happens, lower the ventilation temperature. Additionally there has to be sufficient ventilation in the morning to stimulate the removal of the moisture. On days with less sun sufficient evaporation needs to be encouraged.
Another measure that leads to a more generative crop is to allow a lower water content of the slab. The grower can stop irrigating earlier in the afternoon so that the moisture content in the slab reduces at night. To monitor the moisture content it is important to take measurements. If the slab dries out too much it can lead to a water deficiency.”
Controlling growth with light: more in winter, diffuse in summer
For a grower, every ray of sunlight entering the greenhouse in winter is a bonus. Light is also welcome in summer, provided it is properly distributed throughout the crop. This can be achieved by combining coatings. Two vegetable growers are leaders in this field in the Netherlands.
Adapting climate and watering to coatings
Coatings soften the greenhouse climate; this provides an opportunity to change how the climate and watering are controlled. Two crop advisors discuss the principles that apply to tomatoes, gerbera and alstroemeria.