Sea Holly
Eryngium
Sea Holly blooms from June through August.
Mature size, hardiness zones, sun and the trait tags were checked against named botanical sources for this plant. The bloom months and water need on this page were not.
Growing Sea Holly
Plant it in full sun. It prefers low water. It is hardy in USDA zones 4–9. Expect it to reach about 2.3 ft tall and 1.3 ft wide at maturity, in roughly 2 years.
When to plant Sea Holly
Plant Sea Holly in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. For the middle of its hardy zones 4 to 9 range, spring means March to May and fall means August or September. Once settled, it blooms from June to August.
Month-by-month timing for your zone is on the planting calendar: for the middle of its range, start with zone 6 in March.
Good to know about Sea Holly
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Worth knowing
Despite the spiny, thistle-like heads, sea holly belongs to the carrot family, and its flower head is a modified umbel (the flat carrot-family cluster), not a true thistle. per USDA and PubMed Central
Can you divide it?
NC State lists division as a propagation option, but the deep taproot makes it risky. Other sources say leave clumps alone and grow new plants from seed. per NC State and Missouri Botanical Garden
Zone range varies by source
Sources split on cold hardiness: NC State and Missouri Botanical Garden give zones 5 to 9, while Morton rates it 4 to 8. Near zone 4, winter drainage decides survival. per NC State and Morton
One trait, two jobs
The spiny leaves, stems and bracts deter browsing deer and rabbits, while the same open heads hand short-tongued bees, wasps, flies and beetles easy nectar. per NC State
Prized cut and dried flower
The steel-blue heads and spiny bract collars hold their color and shape when dried, and last a long time in fresh arrangements. per NC State
Self-sows around the garden
It readily self-sows in open ground and slowly wanders the garden. Deadhead the spent flowers if you do not want volunteer seedlings. per NC State
Lean soil keeps stems stiff
Rich soil or shade makes it flop and go leggy, with paler color. Full sun and lean, dry ground keep the stems stiff and the blue deepest. per NC State
What pairs well with Sea Holly
Good companions share its growing conditions and add something it lacks: an earlier or later bloom, a lower carpet in front, or structure through winter.
Rock Cress
Shares full sun and low water; blooms in mid spring, before this one opens; both offer pollinator forage, in different months; evergreen, so the bed keeps its shape through winter.
Goldenrod
Shares full sun and low water; overlaps, then carries the display into mid fall; both are strong pollinator plants; its seed heads stand through winter, for structure and the birds.
Aster
Shares full sun and low to moderate water; blooms in early fall as this one finishes; both are strong pollinator plants, and they feed in different months; its seed heads stand through winter, for structure and the birds.
Rosemary
Shares full sun and low water; blooms in early spring, before this one opens; both are strong pollinator plants, and they feed in different months; evergreen, so the bed keeps its shape through winter.
Flowering Crabapple
Shares full sun and low to moderate water; blooms in mid spring, before this one opens; both are strong pollinator plants, and they feed in different months.
Fountain Grass
Shares full sun and low water; overlaps, then carries the display into mid fall; its seed heads stand through winter, for structure and the birds; taller at 3.3 ft, for the layer behind it.
Pampas Grass
Shares full sun and low water; overlaps, then carries the display into mid fall; its seed heads stand through winter, for structure and the birds; taller at 8.2 ft, for the layer behind it.
Switchgrass
Shares full sun and low water; overlaps, then carries the display into mid fall; its seed heads stand through winter, for structure and the birds; taller at 4.9 ft, for the layer behind it.
Featured in these guides
Explore similar plants
You might also like
Foliage
Design a garden with this
Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.