Here's what Edward Frentz, Champion archer and author Robert Elmer's go-to-guy when it came to yew, had to say about how to season yew wood, back in 1926:
”There is no other way to season yew for bows so good as letting it dry naturally in the air, but the five years customary with English bowyers is by no means necessary. Leave the wood, with the bark on and the ends painted, for three or four months in a room where the sun cannot strike it and where there is no artificial heat. Then remove the bark, reduce the wood to nearly the size you want it, and leave it for another two or three months in a room that is warm but not artificially overheated, such as an attic in the summer. It will then be seasoned sufficiently to work.”
Bowyers of those days cut, seasoned and built yew bows by the thousands, as they were (almost) the only type of bow around, for any type of archery. Chief use of yew longbows then was target archery, practicing for and participating in the American Round and the York Round (Single and Double), ie. shooting up to 280 arrows at distances up to 100 yards in competition. High cast and very high durability (target bows would get shot thousands and thousands of times under all kinds of weather) were a necessity. A six month drying period was deemed perfect for that.
Tuukka