I’ve been unable to determine the parentage of the narrow leafed mahonia, ‘Beijing Beauty’ (below), but suspect its heritage is similar to ‘Soft Caress’ and ‘Narihira’, which are partially or fully bred from Mahonia eurybracteata, that has proved not to be sufficiently cold hardy in this garden despite my best efforts. Possibly, these would survive in a protected spot, but it seems I am incapable of determining what is a protected microclimate. In any case, in multiple locations both mahonias have failed to survive. Leatherleaf (Mahonia bealei) and hybrid mahonias ‘Winter Sun’, ‘Charity’, and ‘Underway’ have survived five degrees or more below zero with minimal injury, but narrow leafed mahonias have failed at temperatures above zero.
Long ago, I discovered that zone 7 cold hardiness ratings are not a guarantee. Some zone 7 plants will tolerate temperatures colder than zero, while others perish at ten degrees. Clearly, cold hardiness determinations are an inexact science, and possibly there is no science to it at all, but a best guess or perhaps even wishful thinking.
In any case, ‘Beijing Beauty’ is beginning to flower in early September, a month or two earlier than ‘Soft Caress’ (above), and giving hope that its lineage might be different enough to include greater cold tolerance. While last winter did not approach zero, this year or next, or at least eventually it will get this cold again, and I’ll learn its similarity to ‘Soft Caress’. I suspect it won’t survive, but I can hope that at least one of four, or possibly all will survive in varied spots through the garden.
Also, I’ve recently planted Mahonia ‘Marvel’, which has a similar lack of information regarding its heritage. But, ‘Marvel’ is clearly a late autumn flowering hybrid similar to ‘Winter Sun’ (above), ‘Charity’, and ‘Underway’, without spines except one at the leaf tips. There is less reason to question its hardiness, as I question the cold tolerance of ‘Bejiing Beauty’, and I suspect I’m not alone in giving a try to plants that have questionable chances for survival.