Plant eryngiums where there is bright light, poor soil and good drainage in order to develop a strong, rigid framework and steely patina.
These plants are good low-maintenance perennial plants for hot dry spaces with good drainage. If grown on damp, heavy soil most eryngiums tend to flop and become a dull, grey-green.
However, eryngiums are very diverse: there are over 240 species worldwide. Try growing one or two sea holly in the driest hot spots you have. Some even do well on clay.
Sea hollies are an unusual member of the carrot family (Apiaceae). They set down deep tap roots and do not like to be moved once planted.
When mature, plants can grow up to 3 feet tall. The plants die down completely in winter and, given good drainage, will return every yfear.
- Water sea holly plants deeply, but infrequently during the first season of growth to encourage the tap root to grow deep into the soil (which is the key contributor to sea holly survival during droughts). Once settled, these plants thrive happily on benign neglect. In fact, fertile soil makes plants lanky, so withhold fertiliser and extra watering.
- Deadheading won’t yield additional blooms. Indeed, faded flowers add winter interest long after the first frost occurs, so it is advised to avoid deadheading. The seed heads last well into winter and add visual interest.
As with many blue flowers, sea holly attracts bees and butterflies. If you use this in a coastal garden, consider planting your eryngiums near a fence or building to provide a butterfly-friendly windbreak.
The genus Eryngium belongs to the Apiaceae plant family. This family contains edible plants like sweet fennel as well as poisonous plants like the water hemlock. The common denominator of the Apiaceae family is that the plants have hollow stems, and that they produce compound umbels, which are small flowers that radiate from a single stem. From The Spruce
Some interesting sea holly trivia: the first known artist self-portrait in the history of Western art, by Albrecht Dürer (1471-1528), shows him as a gallant, well-dressed young man holding in his hand a sprig of sea holly. In Germany, sea holly signifies man’s fidelity and is sometimes considered to be an aphrodisiac. Some art historians think that this portrait was painted by the young Dürer as a gift to his betrothed, whom he married shortly after.
According to Maggie Campbell-Culver’s The Origins of Plants (p.437), the sea-holly Eryngium giganteum arrived in Britain from the Caucasus in 1820 and was eventually popularised by the celebrated woman gardener Ellen Willmott (1858-1934), who was among the first recipients of the 1897 Victoria Medal of Honour, given in recognition for special services to horticulture. Miss Willmott owned Warley Place in Essex, and as a result several plants are called ‘willmottae‘. (Other notable female garden designers and plantswomen of the time include Gertrude Jekyll (1843-1932) and Vita Sackville-West (1892-1962).)
Planting Diary Notes: We planted a sea holly at the allotment in our first summer of 2018. The big guy was worried it had died but we held off digging it out. It returned in 2019 but did not produce any flower heads and its growth was low and slow. We are trying to avoid over-watering as it is planted into heavy clay and probably has less-than-ideal-drainage for a drainage loving plant. We’ve been quite disappointed but in early August 2019 we noticed a second plant that has appeared at the side of the main plant. Hopefully this means it’s diverted it’s flowering energies to producing more plants, and will do much better next year. We can only live in hope! On 19 April 2020 we noticed the first emergent thistle-like leaves of the sea holly. We again live in hope that it will do better this year, but by end July 2020 is still now showing signs of flower formation.
We’ve had better luck with them in our perennial flower beds closer to home. The two varieties of sea holly planted into the back patch along the railway fence in summer 2019 are doing well and have come into abundant flower by late July 2020, as seen in the photo above.
Eryngium planum ‘Blue Cap’ was planted summer 2019 and is in abundant flower in the back patch perennial bed. The description is of an erect, semi-evergreen perennial with thistle-like blue flowers in summer. Grow in non-fertile moist or well-drained soil in full sun. Grows 90 cm high and can spread up to 45 cm.