- You Will Get 150 Seeds Of Pearl Yarrow White Double Achillea Ptarmica Herb Flower Seeds. - Description: - Name: Pearl Yarrow. - Other Common Names: The Pearl Yarrow. - Scientific Name: Achillea Ptarmica Pearl. - Color: White. - Plant Seeds: At 68f. - Bloom Time: June – Oct. - Hardiness Zone: 3 – 10. - Plant Height: 18 - 24". - Plant Spacing: 18 - 24". - Light Requirements: Sun. - Soil & Water Preferences: Average.