The ideal location for them would be on a slope under deciduous trees, or in a north-east facing bed. Full sun, alternating freeze / thaw conditions, water logging in winter, or hot dry conditions in summer will all stress the plants. If you get a lot of freezing, a loose covering of leaves or straw will help. Dividing the plants every two or three years helps also, and is a must for the doubles. Divide after flowering is finished. For best results, feed the plants with a weak solution of high potash or tomato fertilizer every ten days from the time the buds start to form until the first flowers open. A "thank you" feed when flowering ends is recommended, but don't feed late in the season and don't use a high nitrogen fertilizer.