Plant and care for knapweed

Plant and care for knapweed

Plant knapweed correctly

Ideally, you can plant the knapweeds that are grown behind glass in February or bought ready-made in the garden center in the bed from the end of April. Another planting date is late summer, when the earth is deeply warmed. As long as you prepare the humus, nutrient-rich soil in fine crumbs in the sunny location, soak the root balls of the young plants that are still potted in water. So the work continues:

  • Dig small pits at a distance of 30-40 cm, spacious enough for a root ball
  • Enrich the excavated earth with compost, horn shavings, bark humus or guano granulate (€ 6.39 at Amazon *)
  • Pot a knapweed, position it in the middle of the hole and plant it just below the first pair of leaves
  • Pour on and mulch with leaves, bark mulch or grass clippings

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The wild shrub character of a knapweed comes into its own in the rustic clay pot. Use common compost-based potting soil as a substrate and add a handful of sand. Place some potsherds over the opening in the bottom of the pot as drainage.

Care tips

The care program for a knapweed is so straightforward that even beginners among hobby gardeners can cope with it without any problems. All important aspects at a glance:

  • Water regularly when it is dry
  • During the growing season, fertilize in the bed every 4 weeks, in the pot every 2 weeks
  • Clean up withered and faded things promptly
  • Cut back close to the ground after the first flowering period

In autumn or late winter prune the perennial one more time; this time up to 10 cm above the floor. Since the knapweed is completely hardy, there is no need for winter protection.

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Which location is suitable?

If a sunny to full sun location is to be occupied in the garden, the knapweeds are always busy, always blooming. In the deeply humus-rich and nutritious soil, which is often fresh, moist and calcareous, the summer perennials show their most beautiful side.

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What soil does the plant need?

The knapweed expresses its inimitable wild shrub character wherever the soil is humic, loose and rich in nutrients. A slight lime content is just as welcome as fresh soil moisture without the risk of waterlogging. Nevertheless, the robust perennial also tolerates sandy-loamy soil as long as there is a rich population of microorganisms there.

When is the flowering time?

The knapweed puts its distinctive fringed or fluffy flowers in the limelight from May to July. If you can't get enough of the pretty summer shrubs, cut the withered flowers close to the ground after the first blooming period and spoil them with a portion of compost. Thereupon the floral ambassadors of summery lightness call for another appearance on the garden stage.

Cut the knapweed correctly

In order to successfully cultivate a knapweed, secateurs are essential items. We have put together for you all the occasions when the perennial is cut:

  • Cut stems that have just blossomed to at least two leaves for the vase
  • Clean up withered flower stalks as soon as possible to make room for further shoots
  • After the first flowering period, cut back close to the ground for a late summer re-flowering

For the last time in the season, the scissors are used in autumn. Now cut the knapweed down to 10 cm above the ground. If you would like to give the natural perennial enough time for the seeding, move the date for the pruning to February.

Water the knapweed

The knapweed shows little tolerance to drought. So don't let the perennial thirst. As soon as the soil has dried in the upper area, it is watered. Ideally, avoid overhead irrigation so as not to spoil the pretty blooms. The water is poured directly onto the root area with the jug nozzle.

Fertilize knapweed properly

She is by no means one of the ascetics among the summer shrubs. In addition to a balanced water balance, the knapweed also requires a regular supply of nutrients. Fertilize the summer flowers from May until the end of the flowering period in the bed every 4 weeks with compost and horn shavings or plant manure. In the pot, the cheeky blooming beauty thanks you for the liquid fertilizer given every 14 days.


Hobby gardeners rarely have to complain about plant diseases in knapweed. If problems arise, the ubiquitous fungal infection powdery mildew is usually behind it. If you notice the first signs of the floury-gray coating on leaves and shoots, fight it with fresh milk. Water and fresh milk are mixed in a ratio of 9: 1 and applied every 2-3 days with the hand sprayer.


After the knapweed has drawn in its aboveground plant parts in winter or these have been cut off, frosty temperatures cannot damage the root ball. The strongest species can withstand up to - 45 degrees Celsius. Even less robust breeds can still withstand winter down to - 28 degrees Celsius. Protective measures are therefore unnecessary.

Propagate knapweed

Wherever the knapweed has established itself in the garden, there are three uncomplicated methods of propagation. The following overview shows how you can grow more specimens of these charming fringed heads in no time:

  • Division of the root ball in spring or autumn
  • Removal of root cuttings in summer to allow them to take root in the pot
  • Sow seeds behind glass from February

Anyone who knows how to keep pecking birds and voracious pests away from a seedbed can sow them directly outdoors in September. You can look forward to a first bloom of seedlings-propagated knapweed in the second or third year after sowing.

Is knapweed poisonous?

Although Greek mythology reports that the centaur Chiron healed a foot wound of Achilles with a flower of the genus Centaurea, the knapweed does not have healing powers. Likewise, there are no toxic ingredients in flowers, leaves or seeds. The flirtatious perennial is therefore ideal for cultivation in the family garden.

Nice varieties

  • Grandiflora: The cornflower blue flowers paint a picturesque picture in the bed and tub; Growth height 40 cm
  • Major: The fluffy flower balls shine in violet pink towards the sun; Growth height 70-80 cm
  • Jordy: The variety captivates with its extravagant flowers, the edges of which are particularly frayed; Growth height 30-40 cm
  • Alba: A top-class mountain knapweed with pure white flowers from May to July; Growth height up to 80 cm
  • Carnea: An enrichment for the scented garden, because the light pink fringed blossoms smell of peach; Height 40-50 cm