Which plants can go in pots by my northfacing front door?

MATT B SAYS As you want tall plants, try topiary spirals or pyramids, or grow several clematis up a metal or wooden obelisk such as the velvety purple C. viticella ‘Etoile Violette’, which flowers JulSept, or C. koreana ‘Amber’, with yellow and cream flowers in AprJun. Bear in mind that pale flowers keep their colour longer in shade.