Content Detail

Sea holly adds interest to the landscape with their unusual blue coloration and textural appearance. In ideal conditions, this is a profusely blooming summer perennial that attracts bees and butterflies. Sea holly is a great addition to beds and borders, and this plant even does well in containers. They often look a bit like dwarf bushes due to their rounded nature.

  • Family (English) Carrot
  • Family (botanic) Apiaceae (formerly Umbelliferae)
  • Tree or plant type Perennial
  • Native locale Non-native
  • Size range Small plant (6-12 inches), Medium plant (12-24 inches), Large plant (more than 24 inches)
  • Light exposure Full sun (6 hrs direct light daily)
  • Hardiness zones Zone 4, Zone 5 (Northern Illinois), Zone 6 (City of Chicago), Zone 7, Zone 8
  • Soil preference Dry soil, Sandy soil, well-drained soil
  • Tolerances Dry sites, Occasional drought, Road salt
  • Season of interest early summer, midsummer, late summer
  • Flower color and fragrance Blue
  • Shape or form Broad, Mounded, Round
  • Growth rate Slow
  • Wildlife Birds, Butterflies, Insect pollinators

Size and method of spreading:

Sea holly can be between one-half to 3 feet tall and spreads about 1 to 2 feet wide. They can be spread by self-seeding, but deadheading can reduce the likelihood of that occurring. If propagation is the goal, plant seeds in the fall to stimulate growth through winter chilling (stratification). Otherwise, root cuttings can be taken in the late summer. 

Native geographic location and habitat: (include C-value if appropriate)

Sea holly is native to Europe and parts of Asia.

Attracts birds or pollinators: 

Sea holly attracts bees, butterflies, and seed-eating songbirds. 

Leaf description:

Sea holly has leaves that form a rosette at the base of the plant (basal) or near the base (proximal). These basal leaves are dark green in color and are not separated into leaflets (simple). The leaves are long and narrow (oblong to elliptic) and are slightly heart-shaped at the base (cordate). The edges of these leaves are often quite toothed (crenate with mucronulate teeth), sometimes even sharply lobed, but can also be smooth (entire).

Flower description:

The flowers of sea holly are bluish purple and look similar to thistle flowers. The center of the inflorescence is actually composed of tiny flowers arranged in a spherical fashion (head). The individual flowers within the heads are shaped a bit like eggs (ovoid). The petallike bracts underneath the heads of flowers are quite eye-catching, with their spiny edges, and they are often greenish blue to gray-blue in color. 

Fruit description:

The fruit of sea holly are dry, separate, one-seeded segments (schizocarps) with a whitish-tan papery outer layer.

Plant care:

Take care not to overwater sea holly or to plant in soils that are too rich. This is a perennial that can be difficult to transplant due to its taproot. Deadheading can help to improve the appearance of sea holly and can reduce the likelihood of self-seeding. It is good to cut sea holly back in the late summer after flowering has ceased. This is a plant that can sprawl a bit if grown in conditions that are not ideal, including not enough sun and soils that are overly fertile. 

List of pests, diseases, and tolerances:

One disease to look out for on sea holly is leaf spot. If soils are too moist, sea holly can also be prone to root rot. Pests associated with sea holly include aphids, snails, and slugs. Sea holly is resistant to deer and rabbits. 

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