Cerastium tomentosum, Snow in summer, is a vigorously spreading evergreen perennial forming a carpet of slender silver-grey leaves, smothered in May and June with dazzling white starry flowers, attracting bees. Good for trailing down walls and useful for covering sunny banks, but too invasive for all but very large rock gardens.
Height and spread 10-15cm by 60cm (4-6in x 2ft) or more. Native to Italy, including Sicily. Easy and hardy in any well-drained soil in sun. Drought tolerant once established.