How to Grow Sea Holly (Eryngium) Flowers

by Matt Gibson

Take a moment to ponder the sea holly flower. First of all, just look at this delightfully strange-looking beauty. Seriously, just take a moment to drink in this ludicrous but mesmerizing plant. It looks like an alien sea creature that lives in Antarctica. It looks like a blue raspberry wearing a spiky tutu—a Christmas ballerina. This thistle-like flower is a funky and fascinating addition to the garden. Like a giant sunflower or majestic yucca plant, many varieties of sea holly are showstoppers, stars of the show. If you fill a bed with sea holly and place smaller flowers around the border to frame them, the result is breathtaking, or this versatile flower can also play a supporting role.

Native to Europe and the Mediterranean, sea holly flowers bloom throughout the summer, generally ranging from 18 to 36 inches in height with a one-foot base. The sturdy, upright silvery-blue to green stems are crowned by cones in shades of green and blue, which are covered in tiny flowers and thorns and framed by spiny bracts in a host of eye-catching hues (green, white, violet, blue, silver, steel-blue, amethyst, sapphire, and more).

Once established, sea holly requires very little care. Its thorny appearance may suggest that gardening gloves are mandatory when handling it, but this is often not the case. Some varieties of sea holly are a little bit prickly, and grabbing it the wrong way could cause a mild surface scratch. However, most types of sea holly are actually soft to the touch, despite their menacing appearance.

Varieties of Sea Holly

Exciting new varieties of sea holly flowers are revealed each year in an attempt to outdo last year’s lineup of hybrids. There are cool-weather hybrids and warm-weather hybrids of sea holly, and certain types perform well in some zones and not others. Some varieties grow two or three feet, while others tower above the pack at six feet tall. With so much variety and so many new additions, it’s nearly impossible to keep an updated list of the best varietals out there. However, we can still highlight a few of our favorites, both from new hybrid species and from the classic Eryngium varieties.

Giant Sea Holly (Eryngium giganteum)
Just like the sunflower, the giant sea holly is available in a size XXXL, and it is just as odd and fearsome-looking as you might imagine. Dubbed “Miss Wilmont’s Ghost” in honor of English gardener Ellen Wilmont, the giant sea holly grows up to three or four feet—and sometimes higher. This cultivar is most common in a ghostly white but is also available in light blue and is hardy in USDA zones 5-10.

Sapphire Blue (Eryngium sapphire blue)
Growing up to two feet high and one foot wide, the sapphire blue sea holly variety has been a gardener favorite for decades. The sapphire blue variety is hardy in USDA zones 5-9 and boasts intensely vibrant steely blue flowerheads. The upper leaves and stem are also infused with the same ice blue shade as the blooms themselves.

Rattlesnake Master (Eryngium yuccifolium)
Hardy in USDA zones 4-8, the rattlesnake master sea holly grows three to four feet high and two feet wide, producing one-inch white flowerheads framed by narrow, spiny leaves in a basal rosette.

Amethyst Sea Holly (Eryngium amethystinum)
The amethyst sea holly variety hails from Italy and the Balkans, growing one to two feet high and one foot wide. This European native is one of the most cold-hardy varieties in the genus, suited to USDA zones 5-10.The amethyst sea holly produces stunningly deep-hued one-inch amethyst blue flowers surrounded by ice blue two-inch bracts that sit atop silvery blue stems.

Jade Frost Sea Holly (Eryngium planum)
The jade frost variety of sea holly has pink veins and margins as well as variegated, or multicolored, leaves. Growing one and a half to two and a half feet tall and one to one and a half feet wide in USDA zones 5-8, the jade frost variety produces violet blue flowerheads with blue-green bracts atop violet-blue stems that fade to green from top to bottom. Jade frost is a great example of the unique varieties gardeners have come to appreciate due to genetic breeding.

Blue Hobbit Sea Holly (Eryngium planum)
The blue hobbit is one of many varieties of sea holly that were bred to create more dwarf-sized options. Growing only six inches to a foot high and six inches to a foot wide, this tiny sea holly produces purplish-blue blooms with a collar of blue-green bracts from July to September. It tends to produce flowers rather profusely in the summer (especially if deadheaded regularly), then slows but continues producing into the fall in USDA zones 4-8.

Growing Conditions for Sea Holly

Sea holly is one of the easiest perennials to care for, as these flowers are native to harsh areas, such as grasslands, rocky plains, and coasts. Though there is definitely a spectrum of preferred conditions among the many different varieties, all sea hollies thrive in full sun with moist, well-draining soil. Sea hollies prefer a sandy soil, but their long taproot allows them to tolerate drought as well as diverse, even poor, soil conditions. Because of the long taproot, gardeners should plant sea hollies in a permanent location, and be aware that they will not transplant well.

How To Plant Sea Holly

Though you can sow seeds directly into the garden in the fall, don’t be surprised if your sea holly doesn’t bloom during the first spring, especially if you didn’t stratify the seeds. Sea holly grows best when you plant the seedlings, though this can be a challenge. Growing from young plants is only really possible when the plants are very young due to their long taproots, which is why you’ll rarely see seedlings in nurseries. If you’re lucky enough to find them, place seedlings into holes that are several inches wider and deeper than their current root systems. Propagate from root cuttings during the spring.

Care for Sea Holly

Care for sea holly plants is very minimal. They are very tolerant of drought and do not require much, if any, additional watering. Only in cases of extreme heat and drought should sea hollies need the gardener’s assistance in hydration. The only thing that will endanger your sea hollies is too much water, so make sure their soil is draining properly, and in cases of severe rains, you may consider manually draining some of the excess water from the soil.

Sea holly flowers prefer a sandy, even gravel-based soil, though it will adapt to just about any soil type. It’s not a heavy feeder and doesn’t require fertilizer, but it does thrive in soils that are high in organic matter. If you planted your sea holly in soil with low organic matter, consider feeding or side-dressing with compost around midseason to get the most out of your blooms.

The only real care needed from the gardener to promote plentiful blooming is deadheading sea holly blooms as they begin to fade. However, when your plants near the end of the blooming season, usually around mid to late fall, deadheading should cease. The last blooms should be left on the stems—they will look as good as new well into the winter months (retaining their color and shape even though they are no longer alive), and the spent blooms will provide neighborhood birds with a nice bevy of seeds to munch on or store for winter.

Garden Pests and Diseases of Sea Holly

Most of the issues that trouble sea holly are due to soggy, oversaturated soil conditions or excessive humidity. The natural fix is to plant your sea holly in loose, well-draining soil and choose a sunny location that remains relatively dry.

Sea holly has a pretty solid defense system in place to protect itself from garden pests. The only menace known to plague sea holly is the slug. If your plants are situated in a dry and sunny environment, slugs won’t be an issue, though. Bees and butterflies are drawn to sea holly, but deer and rabbits steer clear of its thorny plumage

Root rot and powdery mildew can sometimes be an issue with sea holly, but again, the environment that you choose for your planting site will determine your plants’ susceptibility to contamination. Avoid root rot by maintaining proper soil drainage wherever sea holly is planted. If powdery mildew becomes an issue (which it shouldn’t if sea holly is kept dry and given full sun exposure), treat your plants with a baking soda spray or a milk spray.

Sea Holly for Indoor Bouquets

Sea holly is an excellent choice for arrangements despite its relatively short vase life. Though sea holly dries up after just three days in water once cut, the flowerhead suffers no noticeable wilting or significant color fading when it has dried. After everything else in the arrangement has faded into dust, this thistle-like, thorny flower will retain its full bizarre majesty. Let sea holly dry out completely (use a blow dryer, if possible, to dry the portion of the stem that was submerged in water), and you can even continue to use it for future arrangements. Use compressed air occasionally to keep the dried flowers dust and debris-free.

Check out this video for a short growing tutorial for sea holly:

Watch this one-minute video to learn about how to use sea holly for dried flower arrangements and learn how to get the most out of the fragrance of your sea holly:

This video is full of fun facts about sea holly from an experienced gardener:

Want to Learn More About Sea Holly?

Better Homes & Gardens covers Sea Holly
Gardening Know How covers Sea Holly Plant Care: How To Grow A Sea Holly Plant
Southern Living covers Sea Holly
The Spruce covers How to Grow Sea Holly (Eryngium)