With the great variety of knapweed species, there is something for everyone. With its unusual flowers, the knapweed not only delights us, but also many insects.
The knapweed (Centaurea) is also edible. We give an overview of the most beautiful species and show you how to plant and care for the knapweed.
Knapweed: characteristics and origin
The knapweed (Centaurea) is a genus of plants that belongs to the daisy family (Asteraceae). The genus is distributed in Europe and the Near East and includes about 260 species. These are characterized by their flowers arranged in panicles and clusters, which appear frayed due to the many small individual flowers. The bracts, which are typical of knapweed, are conspicuous and arranged in an imbricated manner. Depending on the species, the knapweed blooms between May and August. She then presents her flowers in colors ranging from yellow to pink to blue. The knapweed leaves can be undivided and lanceolate or pinnate. Some species have green foliage, others silvery or hairy. Knapweed can grow from 20 to 300 cm tall.
Is the knapweed perennial? Yes! Most species of the genus Centaurea are perennials. However, there are also some annual and biennial species.
If the knapweed was fertilized during the flowering period, it produces fruits with long, feathery hairs on them. These hair extensions are also known as pappus. It looks something like the dandelion blowball. This allows the seeds to be carried away by the wind and the knapweed to spread. In addition, knapweeds form stolons, which they use to form large stands.
Tip: Since many species are not yet entirely agreed whether they belong botanically to the genus Centaurea or not, sometimes up to 700 species are attributed to knapweed.
The most beautiful species and varieties
Besides theIn addition to the different types of knapweed, there are many garden varieties that come in a wide variety of colors and sizes. Here we have put together a small overview of the most beautiful species:
- Mountain Knapweed (Centaurea montana): Mountain Knapweed has flowers that are reddish-purple on the inside and blue on the outside . It stays quite small at 30 - 40 cm and flowers relatively early, in May. Mountain knapweed likes to grow in a sunny or partially shaded spot in dry to moderately moist soil.
- Crimson Knapweed (Centaurea atropurpurea): As its name suggests, the purple knapweed (also known as mountain knapweed) flowers ) in crimson. It grows up to 125 cm high and its flowers appear in July and August. The purple knapweed requires well-drained garden soil and plenty of sun.
- Giant knapweed (Centaurea macrocephala): With a growth height of 150 cm, this species grows quite large and otherwise has a strong appearance. It has yellow flowers and originally comes from the Caucasus. It needs a nutrient-rich, fresh soil, which may be humus.
- Meadow knapweed (Centaurea jacea): One of the best known and most common species is the meadow knapweed or common knapweed . They are also often found in the wild. It has purple flowers and is also very popular with bees. The size varies between 30 and 70 cm. Meadow knapweed grows well in dry to fresh soil in full sun. It can even exist on very shallow sub-soils that have only a few centimeters of soil above a layer of rock.
- Scabiosa knapweed (Centaurea scabiosa): Scabiosa knapweed looks quite similar to meadow knapweed. Its flowering period begins in June. It reaches heights of 120 cm. Scabious knapweeds do well in partial shade or full sun on dry to fresh soil.
- White Mountain Knapweed (Centaurea montana 'Alba'): This variety flowers a little longer thanthe wild form, namely from May to July and shines in bright white. It has the same habitat requirements as the species Centaurea montana.
- Granicle knapweed (Centaurea stoebe): This species is heavily branched and bears light purple flowers. The whole plant is covered with fine hairs, the leaves are quite small. It prefers a very permeable, rather stony and dry subsoil in full sun, warm location. The panicle knapweed is to be confused with the panicle knapweed (Centaurea paniculata). However, this is a different species.
- Black knapweed (Centaurea nigra): Unlike some other knapweeds, this species only has flowers of the same length. The name comes from the appendages of the bracts, which are colored black here. The black knapweed needs full sun, especially a warm position and tolerates dry soil as well as fresh soil.
- Bicolor knapweed (Centaurea dealbata): Bicolor knapweed is a mountain plant. The flowers are pink and usually lighter on the inside than on the outside. The bicolored knapweed likes sunny or shady areas in the garden with dry to fresh soil.
Tip: The cornflower is sometimes described as Centaurea cyanus and sometimes as Cyanus segetum . Whether the annual cornflower also belongs to the knapweed genus is controversial.
Planting knapweed: sowing and location
If you want to plant a Centaurea, you should look for a spot in the sun for the knapweed. For some species, such as the giant knapweed, the soil is ideally fresh, loose, humic and rich in nutrients, slightly acidic or slightly alkaline. Other species, such as the black knapweed, on the other hand, need a humus-poor, stony and permeable soil. On particularly sandy soils, it is best to mix in a little clay flour and potting soil.
You can sow the knapweed seeds directly in the garden in spring from April.
Before that, you can also grow the knapweed seeds indoors. To do this, fill pots with soil, press in the seeds slightly and turn one overbell jar above. Keep the whole thing moist and place the container in a warm place at around 20 °C. Germination is usually slow and irregular. After germination you should look for a slightly cooler spot for the plants.
From the end of April, Centaurea young plants can be planted outdoors. A planting distance of about 40 cm should be maintained. Soak the root ball in water before planting. The soil in the bed should ideally be enriched with a nutrient-rich substrate, such as our Plantura organic potting soil. Our soil remains structurally stable for a long time and can store water well, so that the knapweed roots neither become waterlogged nor dry out. It also provides important nutrients. You can also use our potting soil to grow knapweed seeds.
Proper care of knapweeds: cutting and more
Knapweed care consists of classic watering, fertilizing and cutting. So you can enjoy the pretty perennial for a long time.
In a suitable location, the knapweed does not actually have to be watered. However, if it is on very sandy soil or in full sun, it should be watered occasionally.
Fertilization is also important for some species such as the giant knapweed so that it can grow well. It is best to use a slow-release fertiliser, such as our Plantura organic flower fertiliser. This contains all the important nutrients for roots, leaves and flowers and ensures that your flowers thrive. One application in spring and one in late summer is sufficient here, as our flower fertilizer lasts over three months with its long-term effect.
After flowering, you should cut the knapweed so that it can sprout again. A second bloom occurs in early autumn. The cut knapweed is then also ideal as a cut flower in the vase. If you want the knapweed to spread, you should leave the second flower to set seed.
Tip: If you want to use the knapweed as a cut flower, you should cut it just before the flower opens. However, this means that the bees have less of the perennial.
Is the knapweed hardy? Not all knapweeds are hardy. However, the above species have no problem with freezing temperatures. Some others, such as the solstice knapweed (Centaureasolstitialis), but are only annuals and not hardy.
Healing effect and use
The common meadow knapweed (Centaurea jacea) is edible. Leaves, shoot tips, flowers and also the root are used. The bitter substances contained in the roots and leaves are said to promote digestion. For example, a tea can be brewed from the plant parts. In the past, knapweed was also used in medicine to treat scabies and eye diseases. The flowers taste neutral and are often used to decorate dishes.
Is knapweed poisonous?
The knapweed is not poisonous and therefore poses no danger to children or pets. The frequently occurring meadow knapweed is also not a problem on horse pastures.
The cornflower looks very similar to the knapweed and used to belong to the knapweed genus. We show how to plant and care for the cornflower and how to use it in the kitchen.