|What zone are we in Boise? This is one of the questions most frequently asked at the nursery. I tell folks that, despite global warming, I still believe we should be considered zone 5. The photo above, from my front yard illustrates what can happen to a once beautiful zone 6 Rosemary ‘Arp’. This Rosemary had been growing like crazy for several years, and I let it go until it covered the little walkway in the photo. It was glorious–until this spring. And, please note: this rosemary is growing right against a south facing wall.
Hardiness zones are geographical regions defined by average minimum winter temperatures. For example, zone 5: -15, zone 6: -5 and zone 7: +5. By that scale Boise should be zone 7, right?
But–in my opinion–average minimum lows are too simplistic a method of predicting plant survival. Other factors are equally important. The abrupt onset of cold (plants are not ready); extra long winters (like last winter); and early winter warming followed by spring cold–these factors can kill plants even when the actual low temperatures are not even close to the theoretical minimums for your zone.
At Draggin’ Wing, we stick to zone 5 and below, with an occasional zone 6 plant. Our goal is to offer plants that will last through the ups and downs of the seasons–and those ups and downs appear to be getting more extreme!