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Most of the approximately 500 species of the genus of flake flowers (Centaurea) belong to the perennials, some also to the annual and biennial plants. Its natural range is mainly Europe, the Mediterranean and the Middle East. We know the best-known one-year-old flock flower species from our summery grain fields, where it produces a typical picture with its small blue flowers: the cornflower (Centaurea cyanus). In the meantime, however, numerous annual cornflowers with other flower colors are also available on the market.
Flake flowers belong to the Rhizombildenden plants. Some species of flowering plants can form large stocks over time. This includes, for example, the simply called Knapweed species Centaurea dealbata. From the horticultural point of view, the perennial hardy species such as the mountain knapweed (Centaurea montana) and its varieties, the giant knapweed (Centaurea macrocephala) and the dwarf knapweed (Centaurea bella), which is particularly suitable for rock gardens, are of particular interest.
The flowers of the Large-headed Knapweed (Centaurea macrocephala) look a bit like artichokes
The foliage color of the broad lanceolate, summer green leaves varies between fresh green and silvery gray. Depending on the species and variety, the plants belonging to the Asteraceae family may turn white, yellow, pink, pink, purple or blue between May and October. A particularly striking flower color has the mountain knapweed 'Black Sprite'. Their flowers are deep purple colored. The Mountain Knapweed is one of the first to open its flowers and display them until July. The giant knapweed, however, begins at this time only with the flower and holds it until the August. The cornflower blooms the longest, namely into October.
The Mountain Ringlet (Centaurea montana) opens its flowers in May
The flowers are visually reminiscent of thistles that belong to the same family. Particularly striking is the similarity in the yellow-flowering giant knapweed, which carries its flowers on up to 150 centimeters high stems. This makes it one of the largest species of flowering plants. A similar plant height can be reached also the rather rare Knapweed (Centaurea benoistii) and the meadow Knapweed (Centaurea jacea). In comparison, low-growing species such as the dwarf knapweed or varieties of mountain knapweed with heights between 20 and 50 centimeters are downright small. The advantage of this broad growth spectrum: In this genus, the right plant is available for every garden situation - provided that the location is right.
Location and ground
Most flake flowers prefer a sunny spot in the woody edge or open space habitats with a well-drained, loose-humus rich, relatively nutrient-rich soil. Many species are also very lime tolerant.
Because of their natural and wild character, flake flowers are less suitable for the classic perennial discounts. Their full beauty is only in natural plantings on sunny or partially shaded woody edge or in the bed to advantage. The planting partners are here depending on the location. In the penumbra, for example, various species of cranesbill (geranium), Caucasian goat's rue (galega orientalis) or berries are suitable, while in a sunny spot beautiful combinations with steppe sage (salvia nemorosa), iris (iris barbata elatior) or also dyer's chamomile (Anthemis).
Flake flowers are very suitable for cutting, as their flowers also last a long time in the vase. If you want to use the knapweed as a cut flower, you should cut the flowers but before flowering, and the best in the morning, because then the pedicels last particularly long.
If the mountain knapweed is radically cut back after flowering, the plant will bloom again after about 4 weeks. At the same time you prevent so that the plant is silent.
With its blue flowers, the cornflower (Centaurea cyanus) is a well-known image in our fields
Older specimens and those with silvery foliage are split at the beginning of sprouting in spring or fall.
Further care tips
The perennial species are very undemanding. In general, the removal of wilted flowers promotes the formation of new buds in all the bluebells.
Flake flowers are propagated by division or sowing. However, you should always propagate vegetative species so that the characteristics of the original plant are preserved. Older specimens with woody base such as the silver knapweed (Centaurea pulcherrima) can also be propagated by basal cuttings.
Diseases and pests
Occasionally, bluebells are attacked by aphids, rust or powdery mildew.