Outsidepride Dianthus Sweet William Flower Seed Plant Mix - 5000 Seeds Dianthus Barbatus Sweet William flower seeds mix is a perennial grown in USDA Zones 3 - 9 reaching 18 - 24 inches tall. This is a short-lived perennial wildflower that is perhaps best grown as a biennial. These flowers are best grown in deep, organically rich, well-drained soils in full sun, but generally appreciates some light afternoon shade in hot summer climates such as the South. Perennial wildflower seeds may be planted directly in the garden in late spring for bloom the following year. Sow 2 ounces per 1,000 square feet or 6 pounds pe acre for a meadow of sweet william flowers.