Lunatic plants

In A Year at Kew, a cable television series about my soon to be new home, the Royal Botanic Gardens Kew, in London, an experiment was run to see if seed planted at the time of the full moon produced more flower and fruit.

In at least one trial, this seemed to be the case. It was pointed out that was but one experiment and it would need some careful duplication and controls to confirm.

Even if there was a correlation, the next question is whether there is a causal effect. That is, by what means does the moon influence life on earth.

Theoretically it could it be the extra light of a full moon promoting earlier germination? But that would only be for a few nights, and you would think there would be greater variations in light due to clouds and other weather events during the day.

Even less likely would be the gravitational effect of the moon. For example is more moisture dragged to the surface of soil due to the position of the moon relative to the earth. However the difference in gravitational force over the lunar month is, I gather, negligible.

It's often thought that night-flowering cacti flower more often with the full moon. This seems to be wishful thinking. It has been pointed out that there is a one in nine chance of the cactus flowering during a full moon anyway because the moon is at its brightest for about 3 nights. Even with these odds cacti growers say that if you watch enough of these flowerings they don’t really favour the full moon nights.

Again, it would be hard to think of a trigger for flowering with the full moon, although brighter light might help the moths find the flowers and perhaps a growth cycle that takes 28 days could have a trigger at the last time there was extra light around (we know a flash of light is enough to trigger sensitive day-length chemicals in plants). But at the moment, such an explanation isn’t needed.

And one must always remember the maxim: extraordinary claims require extraordinary evidence. Perhaps I could do some extraordinary science when I'm at Kew to test this out?

Image: the culprit, as photographed by NASA. *This posting is from the Radio Archives (November 2008).