- You Will Get 100 Seeds Of Organic Blessed Milk Thistle Silybum Marianum Hummingbird Purple Flower Seeds. - Description: - Name: Blessed Milk Thistle - Certified Organic. - Other Common Names: Milk Thistle / Mary's Thistle. - Scientific Name: Silybum Marianum. - Color: Purple. - Plant Seeds: Outdoors After Frost / Indoors Weeks Before Last Frost. - Bloom Time: Mid Summer - Early Fall. - Hardiness Zone: 5 - 9 (& Reseeds Itself Easily). - Plant Height: 48 - 72". - Plant Spacing: 24 - 36". - Light Requirements: Sun. - Soil & Water Preferences: Average.