Growing a Sea Holly

The plant genus Eryngium contains many species that are commonly named sea holly. This ornamental shrub is known for its thistle-like, pineapple-shaped flower that is surrounded in spiky, often silvery blue bracts (leaves immediately surrounding a flower). Sea holly cultivation has resulted in several beautiful garden varieties, a popular one, Sapphire Blue, known for its striking inky blue flowers and bracts. 

The name, sea holly, actually comes from one species, Eryngium Maritimum, named for its native growth in sandy soil along the European coastal regions. It is used as a common name for other species as well.

Blooming Period

The blooming period varies according to species, but most bloom for about 2 months in the summer. Most sea holly species and cultivars are perennials.

Average Height and Spread

Sea holly grows usually between 18 and 36 inches, but some cultivars have reached several feet high. Sea holly spreads about one foot wide.

Zone Hardiness

The cultivars that can be found in the United States are generally hardy in zones 5 to 9.

Benefits of Growing Sea Holly

Besides for the enjoyment of its unique beauty, there are other benefits to growing sea holly. The flowering shoots and roots of the plant are edible. The shoots are sometimes blanched and are compared to asparagus, while the roots, usually boiled or roasted, have a chestnut-like flavor. The sea holly also attracts beautiful and is not as likely to be eaten by animal because of its spiky leaves. Their flowers are often used in dried flower arrangements. 

Planting Sea Holly

The sea holly can be grown from seed, although it may not flower its first season. The sea holly has an extensive root system and long taproot which can make transplanting difficult, so, if possible, plant it where it can stay the remainder of its life. Sea holly prefers sandy, well-draining soil, thriving in pH levels 6.1 to 7.8. Some varieties are known to grow well in poor soil. When planting seedlings or plants from a nursery, dig a hole slightly larger than the container. Space about 1 foot apart.

Caring for Sea Holly

Sea holly should be watered regularly, although it is drought-resistant due to its long taproot. For those varieties that don't do well in poor soil, applying fertilizer may help with growth and blooming. Propagate by dividing in early spring or fall. 

Common Species of Sea Holly

  • E. Alpinum is native to Switzerland and known for its blue flowers and blue-green foliage. Blooms July to August
  • E. Amethystinum is easily grown from seed and is a small shrub, rarely reaching over 1 1/2 feet tall. It also has blue flowers and foliage. Endures colder climates better than most other species.
  • E. Maritimum is a small shrub, also reaching heights of about 1 1/2 feet tall. Blooms from July to October.