Hogweed

How to recognise it

Habit

Robust biennial to short-lived perennial of 0.5–2 m, with a leaf rosette in the first year and then a branched flowering stem.

Leaf

Large, up to 50 cm, pinnate or deeply lobed with 3–9 broad, toothed lobes; rough and hairy, with an inflated sheath around the stem.

Flower

Flat umbels of 10–20 cm with 15–30 rays. Flowers white, sometimes pink; the outer flowers have larger petals on the outside.

Fruit/Seed

Flat, round to oval seeds of 7–10 mm with a narrow wing and dark stripes, the oil ducts.

Stem

Hollow, ridged and rough-hairy, up to 2–3 cm thick; green or slightly purple-tinged, but without large purple blotches.

Confusion with

Giant hogweed is much larger (2–4 m), with umbels up to 50 cm, deeply cut, sharply lobed leaves and purple-blotched stems. The highly poisonous hemlock has smooth, hairless stems with purple spots, finely divided leaves and a mousy smell. Cow parsley flowers earlier, in April–June, and has fine, fern-like leaves.

Flowering: June–September · Pruning: March and September

Why grow it?

• A real insect magnet: soldier beetles, longhorn beetles, hoverflies, flies, wasps and ichneumon wasps are found on almost every umbel.
• Flowers for a long time, from June into September, and often again after mowing.
• The flat umbels suit insects with short mouthparts, which cannot reach the nectar in deep flowers.
• The hollow stems and dry umbels give shelter to insects and spiders in winter.
• Belongs in a flowery verge, a hay meadow or a wild corner of the wildlife garden.
• It was once used as fodder, among others for pigs.

Hogweed: where does it grow best?

• In the wild: road verges, hay meadows, dykes, woodland edges, rough ground and ditch banks, on nutrient-rich, moist soil.
• In the garden: sun to partial shade, in a wild corner, a flowery verge or at the back of a natural border.
• Moist to damp, fertile soil: loam and clay are ideal.
• Choose a spot where children do not play among the stems and where nobody brushes past the leaves with bare legs.

Goes well with

• Wild carrot: Another umbellifer, finer and lower, for a flowery verge.
• Common knapweed: Purple flowers in July–August for butterflies and bees in the same hay meadow.
• Oxeye daisy: White flowers in May–June, before the hogweed is at its best.
• Common nettle: Food plant of the peacock and red admiral in the same wild corner.
• Tansy: Yellow buttons in August–September in a wild verge.

Hogweed: when and how to plant it?

1. Buy seed or young plants from a native plant nursery. Never dig plants up from the wild.
2. Sow outdoors in September–November, directly where it is to grow: the seed needs a cold period to germinate in spring.
3. Scatter the seed on bare ground, rake it in lightly and later keep 50–60 cm between the plants you leave.
4. Plant young plants in October or March–April and water them well when planting.
5. Wear gloves and long sleeves when moving plants: the sap of young plants can also make skin sensitive to sunlight.
6. Expect only a leaf rosette in the first year; flowering usually follows in the second year.

Care

Water

Only after planting and during long dry spells. After that its deep taproot sees it through.

Feeding

Not needed: on fertile soil it grows big enough by itself.

Mowing

In a verge or hay meadow, mow twice a year, in mid-June and in September, and remove the cuttings. It flowers again afterwards.

Spreading

It self-seeds freely. Cut off faded umbels before the seed ripens if you do not want too many seedlings.

Protection

Work with gloves, long sleeves and long trousers, preferably on a cloudy day or in the evening.

Tip: Put hogweed at the back of a wild corner, away from paths and play areas: you get all the insects without anyone touching the sap with bare arms or legs.

Pruning and mowing

Pruning months: March and September.

When: Mow part of it in September; leave the rest, with hollow stems and seed heads, until March.

How:

• In a wildlife garden, leave some stems and umbels standing over winter: insects and spiders overwinter in the hollow stems.
• Cut off faded umbels in August if you want fewer seedlings.
• In a hay meadow, mow in mid-June and in September and remove the cuttings.
• In March, cut the old stems back to just above the ground, before the new leaves grow large.
• Pile the cut stems in a quiet corner as shelter for small animals.

Caution: The sap makes skin sensitive to sunlight. Wear gloves and long sleeves, even when cutting dry stems, and preferably work in cloudy weather.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow fresh seed in September–November outdoors where it is to grow, or in pots left outside over winter. It needs a cold period and germinates in March–April.

Self-seeding

Let a few umbels ripen: it self-seeds readily. Move young seedlings in spring, wearing gloves.

Hogweed: how does it get through the winter?

Hardy to −30 °C.

• The plant dies back above ground; the taproot survives winter and new leaves appear in March.
• The hollow, dry stems and seed heads stay standing and shelter overwintering insects and spiders.
• Fully hardy: hard frost is no problem.
• Covered in hoar frost, the dry umbels make a fine winter silhouette in a wild corner.

Diseases and pests

• Skin burns: Sap plus sunlight causes red patches and blisters. Wear gloves and long sleeves and wash skin straight away with soap and water after contact.
• Too many seedlings: On fertile soil it self-seeds easily. Cut umbels before the seed ripens and pull out seedlings while young.
• Dangerous look-alikes: Giant hogweed and hemlock look similar from a distance. Learn the differences before leaving or picking anything.
• Aphids: Sometimes aphids on the stems. Leave them: they feed ladybirds, hoverfly larvae and birds.

Through the year

• March: Cut down the old stems. New leaves appear.
• April: The rosettes grow. Plant.
• May: The flowering stems shoot up.
• June: Flowering begins. Mow hay meadows in mid-June.
• July: Full flower, busy with beetles, hoverflies and wasps.
• August: Flowers and first seed. Cut umbels if you want fewer seedlings.
• September: Last flowers. Mow part of it. Collect and sow seed.
• October: Sow or plant.
• November: Leave the hollow stems for overwintering insects.
• December: Rest. Dry umbels in the hoar frost.

Did you know?

• Its English name hogweed comes from its former use as food for pigs.
• The outer flowers of each umbel have larger petals on the outside: this makes the umbel look like one big flower, more visible to insects.
• The genus name Heracleum refers to the Greek hero Heracles, probably because of its robust growth.