Here's a real 'must' for the herbaceous border, rock garden or patio container. Lime-green to white flower buds burst open to reveal large 4cm (1½in) blooms, which are as pure as snow.
Sow from February to June on the surface of a good seed compost just covering the seed with a thin layer of compost or vermiculite. Germination takes 14-30 days at 18-20C (65-70F). Don't exclude light, sealing in a polythene bag after sowing is helpful.