Somehow, I have managed to go through life without once noticing a sea holly. When I saw Don McClane‘s perfectly-captured image of Eryngium leavenworthii, I immediately thought, “what is that, and how can I get one!?”. It turns out species of Eryngium have long been prized by gardeners. Seeds of many species, including Eryngium leavenworthii, are readily available.
Eryngium leavenworthii is native to south central USA. It is found on limestone or chalky soils of prairies, open woodlands, and roadsides. It is an annual or short-lived perennial species that reaches a height of nearly a meter. Eryngium leavenworthii‘s claim to fame is its brilliant purple colour. The terminal flower heads are composed of minute purple flowers and bracts (these turn purple as the flowers open). The stamens are electric blue, and the pineapple-shaped flower heads are subtended by an involucre of brightly-coloured lobed spiny bracts. The tips of the flower heads bear a tuft of small spiny leaves that deepen to purple as the flower enters anthesis.
This species is popular with native plant gardeners in its range. It is drought-tolerant and readily grown from seed. Michael McDowell, who blogs about his Texas native garden, suggests planting this Eryngium behind other prairie plants such as little bluestem (Schizachyrium scoparium) since its stem and leaves can get scraggly. Being an annual, it will likely grow in most climates, but will require extra attention in areas with cool temperatures or high rainfall. Plant it in free-draining, slightly alkaline soils for best results. Soils with too much fertility will cause Eryngium leavenworthii to grow leggy and for the leaves to overwhelm the floral display. If you can grow tomatoes successfully, Eryngium leavenworthii will likely work well for you. The seeds should be sown directly in the autumn or after the last frost in early spring.