^^is there a nursery out there that doesn't appear optimistic on their zone ratings :eek:?
Even when I look at SLN's ratings I hve to raise an eyebrow. They had a number of varieties they'd say were good to -50....I find that rather hard to believe. The pear that I grafted from GRIN (Southworth) this year came from a tree that supposedly survived -45 at least a few times with "no damage". I suppose going by temperature alone many of these nursery zone ratings may be accurate. What they don't (and really can't) take into account are all the other environmental conditions that combine with the temperature. Soil type, average annual precip, typical snow cover (and those years when things aren't typical), unrelenting, desiccating wind, average onset of when below zero temperatures may occur, etc. etc. etc.