-Eryngium planum, commonly referred to as Sea Holly, makes an excellent cut flower and dries well too. After drying, the flowers keep their blue color and work nicely into dried floral arrangements. Sea holly is a 4 foot tall perennial growing in USDA zones 4 - 8. Eryngium also is very attractive to bees and butterflies, and they have a long bloom season. Sea Holly likes a position in full sun, and they are perennials that can reach 48 inches in height. These unique flowers also have a tap root that allows them to be fairly drought tolerant. Sowing Rate: 5 - 6 seeds per plant. Start the seed indoors in early spring, or directly sow the seed outdoors after danger of frost. Press the seed into the soil and lightly cover with peat moss or garden sand. At temperatures between 60 - 72F, germination normally occurs within 28 days. Sea Holly will self-sow, but it is not considered invasive.