Eryngium planum

Eryngium planum is a picturesque blue thistle, which is both charming and prickly! This perennial species offers an abundance of flowers resembling small azure pom-poms on branched steel-blue stems in summer. It is a sculptural and highly decorative plant that will be appreciated in slightly wild areas of the garden or in a rockery. Its steel-blue colour is even more intense when planted in full sun, in poor, rocky, and fairly dry soil. Its flowers are also beautiful in fresh or dried bouquets.

Eryngium planum (synonym Eryngium armatum), also known as blue eryngo, is a plant in the Apiaceae family, just like celery and carrot. It is an herbaceous perennial plant native to the mountains of central Europe. In nature, it is found in dry and sunny places, in well-drained gravelly or sandy soil.

With an upright and bushy habit, it quickly reaches about 80cm (32in) in height and 50cm (20in) in width. Its root develops a rosette of basal leaves with petioles. They are ovate with a heart-shaped base, thick, toothed, dark green, shiny, and evergreen in winter. Tall, dark blue-grey, branched stems adorned with a few small leaf spines without petioles rise from the basal rosettes. The flowering occurs in June-July, at the tips of these branches. It takes the form of ovoid inflorescences, 2cm (1in) in diameter, composed of a multitude of tiny azure-blue flowers, surrounded at the base by thin toothed bracts of the same blue colour with metallic reflections. This flowering attracts many pollinating insects. Eryngium planum easily self-seeds in light and well-drained soil.

It does not live very long (especially in fertile and moist soil), but it easily self-seeds where it pleases. It is superb in the company of Lychnis coronaria, grasses (Stipa, Carex comans, Muhlenbergia), catmints, and shrubby salvias. It pairs very well with roses, primroses, cornflowers, and cosmos, or with tall mulleins in dry gardens. A plant to admire in a countryside border, with its fascinating colour and somewhat futuristic design.