These plants usually grow in the micro-climates found in most yards. My Pieris, for example, grows on the south side under the dryer vent. Gardeners should also take into account that the rating system is not an exacting science. It only takes minimum temperatures into consideration, he says. Temperatures are only collected in a few locations and cannot possibly be indicative of all of Northern Utah.
Many landscapes have micro-climates, or areas that are warmer than their surroundings.
For example, plants on a south facing wall receive some radiation and warmth throughout the winter from the heat reflected off the wall. This can give them a 5 to 10 degrees warmer environment than areas on the north side of the house. Fences, patios and other protective structures can also improve the micro-climate, he adds. Plants in low areas with no air drainage are more susceptible to colder temperatures than those on a slight incline where the colder air does not settle, but drains away from the plants. There are other factors to consider when selecting plants for the landscape.