Brown knapweed

Brown knapweed: how do you recognise it?

Habit

Leaf rosette with upright, branched stems of 40–60 cm; about 40 cm across.

Leaves

Lance-shaped and rough; the lower leaves sometimes coarsely toothed, the upper ones narrow and untoothed.

Flower

Purple-pink flower heads of 2–4 cm; the large outer florets spread out like a ruff. Flowers from June to September.

Scales

Below the flower head sit papery, light to dark brown scales, which give it its name brown knapweed.

Roots

Short, woody rootstock with deep roots, which is why it copes so well with drought.

Flowering: June–September · Sowing: March–April and September · Plants: March–April and September–October · Pruning: March and September

Why grow it?

• A favourite of butterflies such as browns, skippers and blues.
• Bumblebees and bees collect nectar and pollen.
• Long flowering from June to September.
• Goldfinches and other seed-eaters feed on the seeds in autumn.
• Easy to sow in a wildflower meadow and drought tolerant.

Brown knapweed: where does it grow best?

• Full sun; in shade it flowers poorly and the stems flop.
• Poor, free-draining sandy, loamy or clay soil, acid to chalky.
• Dry to moderately moist.
• Rich soil is not good: the grass grows too strongly and crowds out the flowers.
• Plant 30–40 cm apart, or sow it in a meadow mix with other wild flowers.

Light

Sun

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Dry or normal

Size

0.6 m tall, 0.4 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Oxeye daisy: White flowers in May–June, before the knapweed is at its best.
• Bird’s-foot trefoil: Small yellow flowers low down among the knapweed, also excellent for bees.
• Lady’s bedstraw: Small yellow, scented sprays in the same poor soil.
• Wild carrot: White umbels in the same months, good for hoverflies and beetles.
• Yellow rattle: A semi-parasite on grass that holds back its growth, giving wild flowers more of a chance.

Brown knapweed: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or in September–October; sow in March–April or in September.
2. Clear the ground of weeds and, in a lawn, lift a piece of turf so the plant or seed is not smothered by grass.
3. Plant at the same depth as in the pot and firm the soil.
4. Leave 30–40 cm between plants.
5. Sow thinly on the surface, rake in lightly and keep the soil moist until the seedlings appear.
6. Water new plants in well; after that, watering is rarely needed.

Care

Water

Only in the first year, during long dry spells.

Feeding

Do not: in poor soil it flowers best and stays sturdy.

Mowing

Mow a wildflower meadow only after flowering, in September, and remove the cuttings.

Deadheading

In a border you can remove faded heads for a longer display, but leave a few for the goldfinches.

Support

Not needed in poor soil; in rich soil the stems may flop.

Tip: After the September cut, leave the hay on the ground for a few days so the seed can drop, then remove it. This keeps the soil poor and brings the knapweed back every year.

Brown knapweed: when to prune it?

Pruning months: March and September.

When: In September, mow or cut back the faded stems. In a border you can also leave them standing and cut them back in March.

How:

• Mow a meadow in September to 5–10 cm and leave the hay on the ground for a few days so the seed can drop.
• Then remove the cuttings, so the soil stays poor.
• In a border, cut the stems back in March to just above the rosette.
• Leave a few stems over winter for seed-eating birds and overwintering insects.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow in March–April or in September, where it is to grow or in small pots; the seed germinates readily. In an open meadow it also self-seeds.

Division

In March–April or in October, lift older clumps and cut them into pieces with a spade, each with a few buds.

Brown knapweed: how does it get through the winter?

Hardy to −35 °C.

• Very hardy, to about −35 °C: no protection needed.
• The stems die back; the leaf rosette and rootstock overwinter.
• Leave some of the faded stems: goldfinches eat the seeds and insects shelter among them.

Diseases and pests

• Powdery mildew: White powder on the leaves at the end of a dry summer. Usually harmless; cut off badly affected stems.
• Flopping: In soil that is too rich or too much shade. Do not feed, and choose a sunny, leaner spot.
• Crowded out by grass: In a rich meadow the grass wins. Remove cuttings, reduce soil fertility and sow yellow rattle to hold back the grass.
• Aphids: On the shoot tips in spring. Ladybirds usually deal with them; otherwise hose them off.

Through the year

• March: Cut back old stems in the border. Sow or plant.
• April: Sow or plant. Keep seedlings moist.
• June: First flower heads. Butterflies and bumblebees on the flowers.
• July: Full flower.
• August: Flowering. Remove faded heads in the border or leave them for the birds.
• September: Last flowers. Mow the meadow and remove the hay. Sow.
• October: Plant or divide.
• December: Resting. Seed heads for the goldfinches.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The large outer florets are sterile: they are there only to attract insects.
• The name brown knapweed refers to the brown scales beneath the flower heads.
• Goldfinches love knapweed seeds and pick them out of the heads with their pointed beaks.