Blue thistle, also known as sea holly or star thistle, is a plant that belongs to the Apiaceae family, along with carrots, parsley, and celery. It is native to Europe and Asia, but has been naturalized in many parts of the world, including the United States. Blue thistle is not a true thistle, but it has spiny leaves and stems that resemble one. The plant produces spherical flower heads that are blue, purple, or white in color, with a metallic sheen that changes in the sunlight. The flowers are attractive to bees, butterflies, and other pollinators, and can also be used as cut flowers or dried for arrangements.

Blue thistle is a low-maintenance plant that can grow in poor, sandy, well-drained soil and full sun. It is drought-tolerant and deer-resistant, making it a good choice for xeriscaping or difficult spots in the garden. The plant has a deep taproot that makes it hard to transplant, so it is best to sow seeds or plant mature plants in their permanent location. Blue thistle can grow from 2 to 5 feet tall and 1 to 4 feet wide, depending on the variety. Some of the common varieties are:

• Eryngium planum: This is the most widely grown species of blue thistle, with blue-green foliage and steel-blue flowers. It can reach up to 3 feet tall and 2 feet wide.
• Eryngium alpinum: This species has silvery-blue foliage and flowers with spiky bracts that form a collar around the flower head. It can grow up to 2 feet tall and wide.
• Eryngium maritimum: This species is also known as sea holly, because it grows near the coast and can tolerate salt spray. It has gray-green foliage and blue flowers with white bracts. It can grow up to 2 feet tall and wide.
• Echinops ritro: This species is also known as globe thistle, because it has spherical flower heads that are bright blue or purple. It has gray-green foliage with spiny edges. It can grow up to 5 feet tall and 4 feet wide.

Blue thistle blooms from summer to fall, adding color and texture to the garden. To encourage more blooms, deadhead the spent flowers or cut them for arrangements. The plant may self-seed if not deadheaded, but it is not considered invasive. However, some people may find the plant too weedy or prickly for their taste. Blue thistle is generally pest- and disease-free, but it may suffer from root rot if kept in wet conditions. The plant is hardy in USDA zones 3 to 9.

Blue thistle has some benefits for humans and wildlife. The flowers are rich in nectar and pollen, which provide food for bees, butterflies, and other beneficial insects. The plant can also attract birds that feed on the seeds or use the dried stems for nesting material. Blue thistle can also be used as a medicinal herb, as it has anti-inflammatory, diuretic, and antispasmodic properties. The roots and leaves can be made into a tea or a tincture to treat urinary tract infections, kidney stones, arthritis, and menstrual cramps. However, the plant should not be consumed by pregnant or breastfeeding women, or by people with allergies to plants in the Apiaceae family.

Blue thistle can also be used as an ornamental plant, as it adds interest and contrast to the garden. The flowers can be used fresh or dried for bouquets, wreaths, or crafts. The dried flowers can last for years without fading or losing their shape. The flowers can also be dyed with natural or synthetic dyes to create different colors. Blue thistle can be combined with other flowers, such as roses, sunflowers, lavender, or baby’s breath, to create stunning arrangements. Blue thistle can also be grown in containers, as long as they have good drainage and enough sun exposure.

Blue thistle is a versatile and resilient plant that can enhance any garden with its unique and striking appearance. It is easy to grow and care for, as long as it has the right conditions. It is a plant that can withstand drought, heat, salt, and pests, while providing food and shelter for wildlife. It is a plant that can be used for medicine, decoration, or art. It is a plant that deserves more appreciation and recognition for its beauty and benefits.