All About Blue Thistles

Nearly a dozen mixed blue thistle, wrapped up with a soft, larger white flower

Eryngium (Blue Thistle)

Blue Thistle (Eryngium planum) is an herbaceous perennial weed (classed as a dicotyledon) native to eastern Europe. The plant has been naturalized in the United States. The genus name Eryngium is a Greek name for some type of thistle and planum translates as flat. Additional common names for blue thistle include blue devil, blueweed, sea holly, and viper's bugloss. A member of the parsley family, its other related species include Queen Anne's lace, anise, and fennel. While many of these species have strong, pungent odors and are grown for food, flavoring, or medicinal purposes, blue thistle is not fragrant and is not so used.

Growing Recommendations

Blue Thistle has course, spiny, thorny, colored stems that grow 24-36" long. The leaves of the plant are blue-gray and are not parallel-veined. Its distinctive snowflake-shaped bloom contains small steel blue, white or rose-colored flowers with a cone center.

Cold storage at 34-38 degrees intensifies the color of the bloom. The flowers bloom from July through August. To promote maximum blooming, deadhead spent blooms. Good garden companions include white phlox, snapdragons, and wormwoods. These flowers may be easily divided and sown from seeds. Because they self-sow, they spread with amazing speed. The plant is vulnerable to powdery mildew and root rot, so keep the soil moist, but not soggy, and apply a fungicide if necessary. Snails and slugs are attracted to the plant.

Blue thistle is a beautiful cut flower (it makes a great filler in bouquets), that is available most of the year. The vase life for fresh flowers is 10-12 days. The flowers should be harvested after they have fully opened. When arranging, remove bottom leaves if present. Recut the stems, underwater, at an angle and place them in the vase with water treated with florist plant food for maximum vase life. Replace the water every 3-4 days. The flowers may also be easily dried.

Blue Thistle Occasions

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