Flower stalks bloom from top down in summer, lasting through September. The prickly flowerheads are useful for winter drying. Since plants stay in flower a long time, the whole branching stem is eventually covered with mature flowers. The leaves, as well as the deeply bristle-toothed bracts, look like they would be razor sharp, but are actually soft to the touch. Growing Eryngium Plants thrive in open, sunny gardens in any well-drained, fertile soil, putting up with excessive lime, gravel and poor soils remarkably well.
Bad drainage is sea holly's worst enemy.
Plants grown from seed will not flower until the second year. Thereafter, they will self-sow from year to year. Sea holly provides an invaluable architectural touch to the garden. In the border, give Eryngium companions such as purple Allium or purple basil. For striking color contrast, plant it among chartreuse Alchemilla or yellow Coreopsis .