If you enjoy woodland walks, you will have come across plenty of ferns. The next time you see a stand of ferns in a clearing, it is worth pausing to study them for a minute or two.
Spend a moment looking at them from a few angles and you will quickly spot how ferns are very sensitive to light direction. Ferns orientate their leaves to catch as much light as possible.
It is surprisingly easy to use ferns to find direction, once you have got used to this ‘solar panel’ habit of theirs. There is however one important thing to bear in mind to help you from coming unstuck.
Ferns will turn their leaves to face towards the direction that the greatest amount of light is coming from and on average this will be from the south. However… Ferns are like most green plants: they care a lot about light, but less about points of the compass. Ferns are very common in areas of woodland where there is a mixture of shade and light. Wherever it is very shady overall, but there is a break in the canopy, then this will be the direction the ferns will face towards. This effect is very easy to see along the edges of woodland paths, where ferns on each side face towards the path – because most of the light is coming from the break in the canopy overhead the path itself.
So you cannot assume that the ferns are showing you the way south each and every time.
As you walk past lots of different stands of ferns you will soon notice the trend: there is a bias in the way the ferns are orientated, towards the southern part of the sky, whenever this is possible. As a general rule, the more open the sky, the more dependably the ferns will face south.
It’s not complicated, it just takes a bit of common sense and practice. In the picture at the top, we are facing north and the fern is facing towards us, south, to gather as much light as possible. In the picture at the bottom we are looking south and the ferns are facing the same way as us.
The fern you are most likely to see is the Male Fern, Dryopteris filix-mas. It is the one pictured here.