Big Blue Sea Holly

Light Needs

Full Sun

(At Least 6 Hours Of Direct Sunlight)

Mature Height

2 Feet

Mature Spread

2 Feet

Growing Zones

5 to 8

Big Blue Sea Holly, Star Thistle, Blue Sea Holly, or Eryngium x zabelii ‘Big Blue’, is a stunning, low-maintenance perennial, known for its vivid, color-changing foliage. This remarkable Sea Holly produces spiny, basal clumps of silvery-green foliage that unfurls in late spring with thick thistle-like buds. In late summer to early fall, the buds, spiky foliage, and stiff stems take on a purple to bluish tint that deepens and spreads in color as the season progresses, eventually lending these unique plants their vivid color and brushed metallic sheen. Big Blue Sea Holly ranges in height from 24 to 30 inches with an equal spread. 

Native to southeastern and central Asia, Big Blue Sea Holly has a stiff, upright growing habit and is relatively drought and salt tolerant, especially once the plant is established, and makes a great coastal option. It is a low-maintenance, easy-to-grow option that is deer and rabbit resistant and attracts both butterflies and critical pollinators. It’s used by florists and gardeners alike to provide a unique and colorful flair to arrangements and bouquets, and makes an excellent dried flower option. 

Big Blue Sea Holly Care

Big Blue Sea Holly should be grown in full sun and is very tolerant of hot and dry climates and locations. It can be planted in soil that is dry, sandy and well-drained, slightly acidic to slightly alkaline, and has a pH of 6.0 to 7.8. Sea Holly has deep taproots, which make them difficult to move, so make certain you choose an ideal location before planting. The good news is that this means your Big Blue Sea Holly is drought tolerant. Make certain your Sea Holly has adequate soil drainage. Sea Holly will bloom for a longer period if you deadhead the spent blooms. In late fall or early spring, prune the plants at ground level. 

Big Blue Sea Holly Spacing

Big Blue Sea Holly is an excellent option to bring structure and interest to the back of any garden. It should be spaced 2 to 3 inches apart at planting. They look excellent planted alongside coneflower, which can lend them support when they grow tall.