The country is defined in a series of zones, based on the average minimum winter temperature. A plant that is adapted to your hardiness zone is one that can tolerate the lowest winter temperature your zone usually experiences. In general, minimum winter temperatures occur on the north side of a house and maximum summer temperatures are reached on unshaded western exposures. Southern exposures will be the warmest during the winter. On the south side of a house, temperature changes in a given day in winter can be dramatic and may predispose plants to winter damage by stimulating new growth that cannot tolerate a sudden drop in temperature.
Tree canopies protect neighboring plants by reducing their radiant heat loss.
In winter, the microclimate beneath a tree may be several degrees warmer than the surrounding air, and this small increase in temperature could keep some plants alive. Furthermore, the tree's shade during the early morning slows the rate of thaw and can reduce the amount of cold damage to some species. Building overhangs, arbors and fences may provide similar kinds of protection. All plants require some amount of sunlight, but some species need many hours of full sun while others do best largely in shade. Before choosing plants for your landscape, observe how many hours of sun and shade various parts of the site receive.