Banksia integrifolia subsp. monticola

Banksia integrifolia, native to the immediate coastal areas of Australia's eastern side, is one of the better known Banksias in North American cultivation. Growing vigorously to tree size, it may reach 20' or more over time, sporting silver-backed leaves and beautiful, tall cones of yellow flowers. For whatever reason, this species is often supposed (unfortunately, I think) to be one of the hardiest species to cold. In reality the common coastal form starts to have major problems below 25 °F. However there does exist a form that grows exclusively in the New South Wales interior, and in mountainous areas at high altitudes, which has recently been described as the subsp. monticola. This subspecies seems to be extremely rare outside of Australia; indeed, we may be the first in the United States to offer it, though I don't know that for a fact. Long story short, we think this is an exciting new plant combining the exceptional vigor, beauty, and ease of growth of B. integrifolia with vastly improved hardiness and much better promise for colder gardens. We have it from a grower in Canberra that this subspecies is so hardy, vigorous, adaptable, disease resistant, and easy to grow; that he uses it as a rootstock to graft all other Banksias onto. As you might expect, we don't have any exact numbers for hardiness, since this is our first time trying it. But it certainly ought to be hardier than the coastal form, and I'll be surprised if it can't handle at least 15 - 20 °F.