During periods with high light levels there is an aspect of the culture of Cyclamen that is underestimated: the temperature of the leaves of Cyclamen.
What is the situation of plants that are active and in a normal light level?
The leaf temperature is at a level just below the air temperature. This is the result of the evaporation of the water through the stomata, which takes energy (read: temperature) out of the leaves
When, on a sunny day, the light intensity is higher than the leave can handle, it can’t control the temperature anymore. The temperature of the leaves will gradually go up and raise above the air temperature. In that case the plant cannot keep enough evaporation to cool the plant and therefore will close the stomata to prevent wilting.
This results in no water and nutrients uptake anymore until the leave temperature has dropped to a level that the stomata are opened again.
Measure air temperature cyclamen
When you measure the air/leaf temperature on a sunny day you can easily find the leaf temperature is above the air temperature around 10 – 11 o’clock in the morning, despite the shading is being used.
The result of this is that despite the climate looks all right, the plant is not active at all, due to no water/nutrients uptake because of the closed stomata. The hours the plant is active is easily reduced with 3-5 hours per day.
In this case you have three options:
- Combine an outside shading (netting on top of the roof/white paint on the roof, etc…)
- Close your inside shading earlier in the morning, before the leaf temperature is too high.
- You can mist clear water over the plants (no fertilizer added). If you do this, spray like you spray a chemical and not let the water run off the leaves into the centre of the plant.
Probably a combination of the three is the best solution. Schoneveld Breeding strongly advises to use an air thermometer and a leaf thermometer to be able to check how both temperatures develop during the morning/day.