Hard pruning with a view to giving at least some of them enough room to grow. You may even be able to prune alternate ones down to being 'mini trees' and have the others grow over the top of them.Maybe. But if I try to pull them up the back part of the house might fall since all the roots are now going under the house!
I'm going to try and trim them this year and hopefully next year they will give more.
Tree pruning tax: another 2fer. Tassels and Sylvie.