Facing the sun

Photo: A sunflower facing east, 31 December 2008
It's official, the sunflowers in the Royal Botanic Gardens face east when fully opened. About this time last year I was wondering (aloud, with Simon Marnie on Passion for Plants) whether our sunflowers did what they were meant to do or not.

In bud, the flower-head (a collection of tiny flowers with bright yellow bracts) tracks the sun during the day, but tends to be about an hour behind. Every morning it resets again to east.

But once the flower opens fully, its position doesn't change. Common wisdom is that this position is facing east so that the flowers remain cooler all day (protecting its pollen), facing the morning sun to dry off any overnight moisture and help avoid fungal attack.

When I looked at the sunflowers in the botanic gardens last year, I was sure most were facing the path – west or east, depending on which side they are growing on. I had surmised they were attracted towards the sunlight, which was strongest along the path.

This year we have only a small crop and I am basing my observations on two plants on each side of the path, but all four have their flowers facing east. So what happened last year? Maybe I saw a couple of abherent plants. Maybe there was less light due to crowding and some flower-heads were facing where they could get most light and warmth.

For now, I'm going to accept that the flower-heads of sunflowers face east when fully opened...but be on the look out for exceptions to the rule!