Dark mullein

Dark mullein: how do you recognise it?

Habit

Short-lived perennial or biennial 80–120 cm tall and 40 cm wide, with an upright, usually unbranched flower spike.

Leaves

Rosette of long-stalked, heart-shaped, dark green leaves with toothed edges; smaller, almost stalkless leaves on the stem.

Flowers

Yellow flowers 2 cm across in long, narrow spikes, from June to September.

Stamens

Purple, woolly-haired stamens, characteristic of this species.

Roots

A deep taproot: it tolerates drought but does not move well once older.

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

Why grow it?

• Flowers from June to September, long and generous, with slender spikes that give the border structure.
• A native species: excellent for a natural garden.
• Bees and hoverflies collect the pollen from the flowers.
• Drought-tolerant and robust, even on poor, chalky soil.
• Seeds itself around, giving you free new plants.

Dark mullein: where does it grow best?

• Full sun to light partial shade; the sunnier the spot, the sturdier the spikes.
• Well-drained soil: sand or loam, even poor and chalky soil; acid to chalky.
• Dry to normal soil; it dislikes wet feet, especially in winter.
• Allow 40 cm per plant and leave enough space for the rosette to get light.

Light

Sun and partial shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Dry or normal

Size

1 m tall, 0.4 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Sage: Purple spikes in the same sunny, dry border.
• Catmint: Blue-purple flowers and grey foliage, drought-tolerant.
• Yarrow: Flat heads in yellow or white against the upright spikes.
• Feather grass: Fine grasses create a natural, airy feel.

Dark mullein: when and how to plant it?

Plant in March–May and September.

1. Plant in March–May or in September, when the soil is neither frozen nor waterlogged.
2. Dig a hole as wide as the root ball; on heavy clay, improve with coarse sand or grit.
3. Set the plant at the same depth as in its pot, with the rosette just above soil level.
4. Space plants 40 cm apart.
5. Water a little after planting, then only during prolonged drought.

Care

Water

Rarely needed once established. Water only during long dry spells in the first year.

Feeding

Not needed: on poor soil it stays compact and flowers more freely.

Mulching

Use grit or bark only in a thin layer around the rosette; keep the crown clear to prevent rot.

Support

In a sheltered, rich spot a tall spike can topple; a stake then gives support.

Self-seeding

Leave a few stems to set seed if you want new plants; cut the rest after flowering.

Tip: Let a few stems go to seed: the plant is short-lived, and this is how you keep it in the garden. Cut the other spikes back after flowering.

Dark mullein: when to prune it?

Pruning months: March and September.

When: After flowering, in August–September, with an optional tidy-up in March.

How:

• Cut the faded spikes back to below the lowest flower; side shoots sometimes flower again.
• Leave a few spikes standing for seed and as winter decoration.
• In March, remove the dead stems just above the rosette.

Caution: It seeds itself freely and readily hybridises with other mulleins: cut off the spikes before the seed ripens if you do not want seedlings.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow in April–May outdoors in a sunny spot: scatter the seed thinly on loose soil and press it down without covering. The plant usually flowers in its second year.

Moving seedlings

Move young seedlings in spring with a root ball, before the taproot goes too deep.

Dark mullein: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection is needed in Flanders.
• Wet winters on heavy clay are the main risk: provide good drainage and the rosette will survive.
• In a pot: use soil with plenty of coarse sand and do not stand the pot in a wet corner.

Diseases and pests

• Slugs: Nibbled young rosettes in spring. Collect them in the evening and scatter coarse sand or grit around the plant.
• Root rot: A limp, brown rosette in wet soil, especially in winter. Plant in a dry spot or improve the drainage.
• Caterpillars: Striking yellow caterpillars with black spots, those of the mullein moth, can strip the leaves. Usually best tolerated; you can remove them by hand.
• Powdery mildew: White powder on the leaves in muggy, damp summers. Allow space and remove affected leaves.

Through the year

• March: Tidy dead stems. Plant. Move seedlings.
• April: Sow outdoors. Plant.
• May: Sow. Plant. Protect rosettes from slugs.
• June: Flowering begins.
• July: Full flower.
• August: Flowering. Cut off faded spikes or leave them.
• September: Plant. Last flowers.
• October: Move or thin out seedlings.
• November: The rosette stays green; do nothing.
• December: Rest.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Mullein flowers generally contain no nectar but plenty of pollen, which mainly attracts bees and hoverflies.
• The purple, woolly stamens are the most striking feature of the dark mullein.
• The yellow caterpillar with black spots of a moth, Cucullia verbasci, lives on mulleins.