RE: which zone is best!
If I understand correctly, the zone is based on the average lowest
temperature. It does not really provide information about the highest
summer temperatures. While the harsh winters in Indiana make whole
categories of rose growing impossible, the high summer heat, and strong
direct sun kills other types of plants, like pansies, sweet pea, etc...
In addition the unpredictable freeze/thaw throughout the
winter brings other problems. The clay soils here hold moisture during
the winter in such a way as to exacerbate the consequences of cold. So I
think that the zone number itself is an OK, but limited way
to assess real growing conditions. Judy Sylvester, zone 5