How doI move a Dwarf weeping willow (salix caprea pendula)

Welcome to GOY. It is unwise to move it until leaves have fallen. February would be best but it is fairly safe anytime once leaves hgave fallen and tree is dormant..

Agree that you need to wait until the leaves have fallen before you do anything. You also need to take the biggest root ball that you can. Living where we do I'd probably move late October early November time as the ground would be far too cold and possibly frozen in Feb. You'll need to keep a close eye on it for the next year and water regularly.

thank you for the advice. i live in Dorset (UK) so the weather is fairly good. I understand the point about the leaves dropping, but do i need to cut the root ball and leave it for a month before I cut the tap root. would this help the tree to recover faster.

I don't think you need cut the root ball as long as the tree is dormant.. I doubt if there will be a tap root as this is usually grown elsewhere before planting in your garden.