North and east facing walls can be dry places since they often have a rain shadow at their base. It is best to plant in moisture retaining soil about 18" away from the wall especially if over hung by the eaves of a house where rainfall is unable to penetrate. East walls receive sun first thing in the morning, this can cause considerable damage to frozen leaves buds and flowers as the suns rays quickly thaw out growth, making them rupture and turn black. On a north wall the temperature rises slowly so is much less likely to cause damage to frozen growth, it is wise to take account of these facts when selecting plants and only plant the more hardy or latter developing types on the east wall.