Hobby gardeners don’t like thistles in the garden at all. Ornamental perennials similar to thistle, such as sea holly (Eryngium alpinum), are an exception. In company with other flowering perennials, sea holly visually enhances every border. The shrubby growth and the simple inflorescences give the perennial border a special attraction.
Profile of alpine sea holly:
Scientific name: Eryngium alpinum
Plant family: umbellifers (Apiaceae)
Other names: alpine eryngo, queen of the Alps, alpine thistle
Sowing time: autumn
Planting time: year-round in frost-free soil
Flowering period: July to August
Soil quality: stony to sandy, dry to fresh, calcipholous, nutrient-rich
These information are for temperate climate!
Use in: flower beds, bouquets, border, rock garden, natural garden
Winter hardiness: hardy
Plant characteristics and classification of alpine sea holly
Origin and occurrence
The alpine thistle occurs naturally only in mountainous areas, in the Alps as well as in the Jura. It is native to Central Europe.
Plant order of alpine sea holly
From a botanical point of view, the alpine sea holly (Eryngium alpinum) belongs to the umbellifers, family Apiaceae.
Characteristics of alpine sea holly
Alpine sea holly reaches an impressive 50 to 80 cm (20 to 32 in) in height. Like all members of the genus Eryngium, the prickly perennial is a thistle – it is also known as “alpine thistle”.
The foliage consists of egg-shaped to heart-shaped basal leaves with irregularly serrated margins and often blue-white veined, lobed stem leaves. In autumn the alpine thistle sheds its leaves.
The heyday falls in midsummer with July and August. On a strong and often slightly bluish flower stem, egg-shaped to cylindrical and also blue flower umbels develop. They are surrounded by blue, faintly spiky, pinnate bracts and a collar.
When the seeds of Eryngium alpinum are fully ripe, they fall off together with the flower heads and are thus spread by the wind.
Alpine sea holly – cultivation and care
Choose a sunny place in the garden for the alpine sea holly, it is very light-hungry.
Alpine thistle not only tolerates lime-rich soils, it prefers to thrive in them. The soil should be moderately nutrient-rich, deep and very permeable – a secure drainage of water is pretty much the only thing that the undemanding perennial cannot do without.
The species are sown in flat pots or bowls of sand in autumn. So that the seeds get their necessary cold stimulus, they are placed outdoors in a place protected from wind and precipitation.
The recommended planting distance varies slightly depending on the variety. On average, you plant four plants per square meter (3×3 ft) of bed area.
You don’t have to divide the perennial. The varieties of Eryngium alpinum can, however, be propagated well by this.
Watering / Fertilization / Care
You won’t have any maintenance effort with alpine sea holly: Eryngium alpinum does not need fertilizer or water at suitable locations. If you don’t want the perennial to self-seed too much, you have to remove faded flowers regularly.
Diseases and pests
Plant diseases and pests hardly affect alpine thistle. Even snails leave the defensive perennial untouched.
The alpine sea holly is hardy enough for our climate and can withstand temperatures down to minus 28 °C / -18 °F. Winter protection is therefore not necessary.
Use in the garden
As a frugal survivor, the alpine thistle has a permanent place in the rock garden, in the alpine garden and in the prairie garden. As a tall, structured plant, it can also be used for sunny borders, where it directs the view upwards in the background. Florists value the perennial as a distinctive dried flower. In the natural garden, it magically attracts bees, butterflies and other insects: Eryngium alpinum is a valuable bee-friendly plant.