In 2017 a Swiss willow enthusiast from Boise, Idaho named Walter Buechler allowed me to take cuttings of a male clone of Salix babylonica that he received from another Swiss Salicologist, Heinz Oberli (whose collection of 100 Salix species probably no longer exists). I did not expect it to survive our Zone 3 winters, and sadly it was badly damaged in -20°F temperatures. It had been the most vigorous Salix amongst a collection of around 50 willows from Walter. So I now believe it is a Zone 5 willow (perhaps Zone 6) Herr Oberli collected cuttings of this plant from the Langtang Valley in Nepal at 3450 meters (11,320ft), the reason for its unusual hardiness. After consulting Walter about a clonal name for this selection he requested that it should be called ‘Oberli’ in recognition of the great Salicologist who made this extraordinary find. In Spring 2019 I had a few cuttings of this clone available, as I want to use the rest to build up stock of this great selection. The true species Salix babylonica is sold in North America but it is not hardy in zones colder than Zone 6, there are many other weeping willows sold under this name in Northern States that are mis-labelled and are hybrids of Salix babylonica.
description credit goes to Michael Dodge