I'll plant the spuds on Good Friday!

I'll plant the spuds on Good Friday!, originally uploaded by Rhian vK.

Why?
Because it's traditional, at least in the UK.
I never really understood this, as the date of Easter varies so much. I
figured people did it because it was a public holiday, and so they weren't at
work.
But here's another idea.
Easter is set according to the moon, and at least here in France many
people plan their gardening around the lunar calendar! So maybe that's the reason!