Now, we've talked about macroenvironment , the big climate picture, but there are ways of trying to bring thru plants that are warmer by nature than the rest of the area, or your garden. Most gardens have hot and cold spots. These microenvironments are often a zone or more warmer or colder than the prevailing zone, and so may be able to support special plants that you really would like to try. Full sun areas that face south, especially those close to walls, are usually warm. If you have pets, you can get to know your own garden's microsystems pretty soon.
Cats know microsystems.
On a sunny cool spring day, they will always find the warmest spot. And in the heat of summer, you'll find them in the cool zones. I am not recommending zone extension as a matter, really, for only experienced gardeners to delve into. In fact, anyone who is taking a novel plant unsuited to their zone and trying to nurse it through is on new ground. But experiments like this might be best later when you have invested in the spine of the garden you wanted.