Canna lilies are striking perennial plants with large banana-like leaves and amazing, exotic-looking flowers that are produced over summer. They thrive outdoors in Britain over summer, as long as they are brought inside for winter (a greenhouse or shed is perfect). They love a sunny spot and moist but well-drained soil. Add lots of compost or well-rotted manure before planting. They are great for pots, or can be planted in the ground if you lift them each autumn.