Many agapanthus growers in cold areas like yours bring their plants inside a few weeks after the first frost, and find a part of the house that is cool (about 50 deg F) and dark throughout the winter – a cellar, garage, or bulkhead – and leave the pots there. You may water once during the winter, or not at all. When temperatures rise again in the spring bring them out again and provide the usual summer care (a rich well-drained soil mix, full sun, lots of water and a snug pot).

Courtesy of NYBG Plant Information Service