What effect will it have? Little to none, to be honest. Anything that's hardy in a zone 9 is usually hardy in zone 10.

The hardiness zones are only a reference to low temperatures in winter and gives an idea of what plants can survive at those temps. For the rest of the year the zones are essentially useless. Plus, not all areas in the same zone have the same climate. A zone 7 or 8 in the Pacific Northwest is very, very different than a zone 7 or 8 in the Southern US. Different frost dates, different rainfall amounts, different summer temps, different humidity, etc.

Rodney

Yes, it's a tool. Depending on which map I look at, I'm either zone 4 or 5. So I have now learned from experience and reading that anything zoned 3-6 is a perennial (although there's no guarantee). Anything 7 and above for me is an annual. Several summers ago I bought a passel of Gerbera Daisies. The tag read, "Perennial." I babied them all summer. Not one came back. They were only perennial in Florida! It's a good question, though. It's a little like the chicken and egg question! Heidi