The hardiness zones presented alongside the plant descriptions in this catalog are intended to give a general indication of an individual plant’s cold tolerance. Defining plant hardiness is something of an inexact science. In essence, hardiness zones provide customers with a sense of how well a plant may fare at the coldest end of any given zone. Anyone who has gardened long enough however, knows that such numbers are by no means definitive. Most gardeners know of someone who has defied the odds by successfully growing a plant that is not supposed to be fully hardy in their zone. In fact, it is easy to push the envelope with some plants simply by understanding their needs and matching those requirements to an appropriate spot in your landscape.
For instance, if you were to consider purchasing a rhododendron that is labeled as hardy to -15 F, it does not follow that the plant will perish if the temperature drops to -16 F or even to -20 F. What it means is that if you live atop a sunny hill that gets blasted by winter winds, you should probably think twice about taking that plant home with you. Your next door neighbor, however, who lives near the bottom of the hill, ringed by tall pines, where the soil is dark and humusy, might do well to purchase such a plant. The bottom line is that there are many factors other than temperature minima that can influence the health of your plants; soil quality, moisture and nutrient availability, and exposure to sun and wind all play a part in determining whether or not a plant will thrive in its environment. Appropriate siting is always key, and a little extra attention for the first season will do much to help insure the success of your plants.