|Grown for its white, semi-double flowers with green underneath. This popular, long-lived perennial with a woody base reaches 4 to 5 feet tall. Plants in areas with harsh winters will benefit from a fall mulching. Staking may also be necessary, especially to keep arching plants upright after a rain. Divide in fall or early spring. Slow to establish, but then spreads rapidly. Sometimes referred to as 'Geante des Blanches'.