Zone question for climbing roses
According to the USDA map, I'm supposed to be in zone 6. Nearby Spokane, WA is zone 5b. The problem is, it's always colder here at night than it is in Spokane (about 10 degrees on the average). We live on a farm, in a small valley with a creek behind the house. It often gets very cold here in January/February. Every other year or so (at least lately) it gets down to about -27 F.
Should I consider myself zone 6, or play it safe as zone 4a? It makes a BIG difference when looking for roses :)