The willow wigwam that I made at Pam Goddard's workshop at the Five a Day Market Garden earlier this year has started sprouting. Pam warned us this would happen if we didn't treat the ends of the uprights. I decided to let it be and see what happens, although I shall keep a close eye on it to make sure it doesn't go too mad and hinder the growth of the peas.
Pam suggested soaking the ends in wood preservative but I have also read that letting the whole thing dry out completely before putting it into the ground should stop the sprouting. A Facebook friend wondered if boiling the ends would work. I wondered if that might make the supports more susceptible to rotting. However, another friend found an interesting article that includes a description of the "buff" willow process, which involves boiling (Willow for Basketmaking and Structures). All fascinating stuff.