As we are now in the period of the longest days of the year it’s worth revisiting light and how it impacts the plant.
Photosynthetically useful light is measured in Micromoles per square meter per second (µmoles/m2/s). This is a unit of the intensity of the light and can range in the UK from 0 (pitch black) to 2000 (bright, intense sunshine).
Just like all the other elements of plant growth there is the “Goldilocks zone” not too little and not too much but just right.
It’s obvious with Fertiliser and Water too little is bad and too much is bad and there is a goldilocks zone but previous to looking into this I didn’t give too much thought to light.
I had a pretty good understanding that shade was bad but too much light??
The above graph shows the plants ability to photosynthesis plotted against light levels. It shows how at around 600 µmoles/m2/s the plants ability to photosynthesise stops increasing.
When the plant is exposed to those levels of high light which is more intense and hangs around for longer the photosynthetic machinery within the plant can become damaged. This is particularly noticeable if the plant is already stressed. The most obvious case being moisture stress and the visible symptoms of wilt which are in all but extreme cases seen when light levels get above 600 µmoles/m2/s .
600 µmoles/m2/s isn’t particularly intense light and in my next Blog I’ll have a look at how often we see this levels of light intensity.