There are not many plants as striking as the blue thistle like Eryngium planum. The evergreen amethyst coloured sea holly is a real show stopper with its pretty purple tint and fascinating silver foliage. This plant is native to central and southeastern Europe as well as Asia and its name comes from the Greek word hruggion which translates as ‘a spiny leaved plant’.
This plant is one that does well in most conditions but it is a best known for being a great choice for the seaside garden. I found this plant at the Western Plant Nursery, which is situated on the Wild Atlantic coast of Ireland, where owner Jack Cunnane specialises in growing hardy plants for the coastal garden.
Coastal gardens are tricky to plant up with their exposed locations and salt laden winds and at Jack’s nursery the plants get hardened off over time so that they can withstand the strong climatic conditions of the West Coast.
I have used many Eryngium varieties in my coastal schemes and as long as they don‘t get too much frost, they cope really well with the salty air. Interestingly we have a native variety of Sea holly, the Eryngium maritinum, or Cuilleann trá in Irish, which grows wild on the coast. This variety is a lot less showy than the planum and has more silver green flower heads as well as much more thorny thistle leaves.
All Eryngiums require a well draining yet humus rich soil which should not be waterlogged in winter. The best location to plant this variety for striking flowers is in a more protected area in the coastal garden such as beside a hedge. Then you’ll get lots of striking purple flowers, which are a real favourite of florists as they add an interesting structure and a blue touch to bouquets.
The Eryngium planum grows to about 60 to 75cm tall and will spread to about 45 to 60cm. From a design point of view It is a brilliant plant to add to the border for structure and when planted amongst contrasting plants such as grasses it becomes a strong textural addition. I love planting it with purple spires of Verbena hastata, Russian sage and some soft grasses which give a great contrast in shape and movement. The beautiful Deschampsia cespitosa ‘Goldtau’ is a great choice as a companion. In simpler, more formal schemes I also love to plant them into a bed of pebbles where the plant is allowed to stand on its own for a striking effect.
One of my absolute favourite parts of this flower is that the seedheads look so incredible in the Autumn months and if you leave them to stand they become a stunning structural part of planting scheme. Planted together with grasses for contrast, they not only make a strong architectural statement but also provide a source of food for wildlife as butterflies and bees love them.