Blue thistle: planting, maintenance, care

Plant ID card
Botanical name	Echinops ritro or Eryngium planum.
Common name	Blue thistle, Azure ball, Azurite (Echinops ritro), Panicaut (Eryngium planum).
Family	Asteraceae (Echinops) or Apiaceae (Eryngium)
Origin	Europe.
Dimensions	Up to 70 cm in height.
Foliage	In Echinops ritro, the foliage is deciduous with green-gray, jagged leaves with spiny edges. In Eryngium planum, the foliage is evergreen, with a rosette of dark green, oval, serrated basal leaves and small prickly leaves on the stems.
Bloom	Flowering takes place from June to September depending on the species of blue thistle. The flower stalks can be spherical or ovoid, carrying a multitude of small blue-purple flowers, very honey-producing.
Exposure	Sun.
Ground	Light, dry, drained, neutral to limestone.
Rusticity	Up to -23°C for the Panicaut and -18°C for the Boule d’azur.

Naturally present throughout Europe, thistles are wild flowers accustomed to poor and dry soils. Rustic and resistant, known for their prickly foliage, these flowers do not fear the cold or lack of water: they can be grown in any garden!

What are the different species of thistle?

The name blue thistle refers to numerous flowers, most of which are distributed between the genera

Echinops and Eryngium.

The

Echinops

genus is recognizable by its spherical, pompom-shaped inflorescences, appearing at the top of long, erect stems. Its name comes from the Greek

echinos

and

opsis

, meaning “hedgehog-like”. This characteristic shape and color earned it the nickname

Boule d'Azur

, particularly for the species

Echinops ritro.

It is divided into several subspecies (

subsp.

):

ritro

,

ruthenicus

and

siculus,

as well as different varieties ('

Veitch's Blue', 'Blue Globe'

) with various shades of blue.

The genus

Eryngium

, better known as

Panicaut

, is distinguished by its oval-shaped flower stalks, composed of numerous small azure blue flowers. It is divided into many species, including:

• Ergynium alpinum

  , the Alpine blue thistle, known for its intense blue;

• Eryngium bourgatii

  , the blue thistle of the Pyrenees, appreciated for its very jagged foliage;

• Eryngium yuccifolium

  ,

  the Yucca-leaved panicut, with elongated leaves and white flowers;

• Eryngium planum

  (synonymous with

  Eryngium armatum

  ), the flat-leaved Panicaut, recognizable by its rosette of basal leaves.

The most widespread species,

Eryngium planum

comes in many varieties. The

'Blue Glitter'

variety

is prized for its intense, long-lasting blue, which makes it an ideal bouquet flower. The Dwarf Panicaut variety

'Blue Hobbit'

offers a bushier habit, not exceeding 30 cm in height and spread.

Where to plant blue thistle?

Blue thistles appreciate a sunny, even very sunny exposure. Copyright (c) 2022 Happy Dragon/Shutterstock. No use without permission.

Hardy and resistant, blue thistles can easily be planted in most gardens:

• Exposure:

  blue thistles appreciate a sunny, even very sunny, exposure. If you are unsure between the two species, know that Azurite can tolerate a little shade;

• Soil:

  both species of blue thistle flourish in light, drained and dry, even stony, soil. In heavy soil, consider adding a little gravel to your garden soil at planting time;

• Location and use:

  Blue thistle is the ideal flower for a wild-looking meadow. It immediately creates a country atmosphere in the garden, in addition to attracting pollinators. Combine it with perennials with yellow or orange flowers (Rudbeckia, Solidago, Gerbera) for a beautiful harmony of colors.

How to care for blue thistles?

Blue thistles are wild flowers naturally present in our countryside; robust, they therefore grow alone without requiring any real maintenance. However, some care can extend their flowering period.

• Watering and fertilizing:

  as blue thistles like dry environments, it is not necessary to water them. Likewise, no addition of compost is useful for their development;

• Pruning:

  cut back the clumps after flowering, between August and September. This is the best way to avoid being invaded by thistles the following year!

How to propagate blue thistle?

Blue thistle multiplies by spontaneous sowing: when they fade, the flowers drop seeds which will give new plants the following year. Copyright (c) 2023 Alex Manders/Shutterstock. No use without permission.

Blue thistle multiplies by

spontaneous sowing

: when they fade, the flowers drop seeds which will give new plants the following year. Once the plant is established in your garden, you do not have to do anything to obtain new

blue thistle

shoots .

How to keep thistles blue?

Naturally, blue thistle flowers eventually wilt and lose their beautiful color. If you want to keep them in a bouquet, you must then take care to cut them at the right time and

dry them properly

to preserve their azure blue.

It is in fact recommended to collect the blue thistle flowers in dry, sunny weather, and to dry them upside down, in a ventilated room and

protected from light

. You can wrap them in newspaper to protect them as best as possible.