Wassailing in Yorkshire
 

To wake up the apple trees and drive out evil spirits from
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the orchard the trees need beating.

We do this every year in our (North Yorkshire) garden - thrash all the fruit trees, not just the apple trees, thank them etc.
Wassail!

:-)

One January when I was staying in Hope Cove south Devon my friends and I went Wassailing on Twelfth Night in Totnes. The crowd followed through an orchard while the young 'Apple queen' (Not sure her official title) was carried on the shoulders of different men as she beat the trees. Afterwards everyone returned to the pub for Morris Dancers and lots of food and (LOTS) of drink. Soooo much fun

There's an old saying about beating walnut trees too, but I won't quote the offensive rest of it.

Might it be that beating encourages the sap to flow a bit faster?

probably more to do with driving the evil spirits out, drive away the fear of winter, a bit of illicit sex and a bit of submerged tree worship.