Common hemp-nettle

How to recognise it

Habit

Annual, 20–80 cm, upright and often branched.

Leaf

Opposite, oval to lance-shaped, 3–10 cm, coarsely toothed, hairy and stalked; looks like a nettle leaf but does not sting.

Flower

Whorls in the upper leaf axils, from June to September. The flowers are 15–20 mm, pink to purple or white, with a dark-patterned lower lip, a yellow patch and two hollow bumps at the base.

Fruit/Seed

Four smooth brown nutlets ripen inside the spiny calyx.

Stem

Square, with stiff, downward-pointing hairs and swollen, often reddish, glandular nodes.

Look-alikes

Bifid hemp-nettle has smaller flowers with a notched middle lobe on the lower lip. Dead-nettles have no swollen nodes and no spiny calyx teeth. Common nettle stings and has small green flowers in drooping strings.

Flowering: June–September

Why grow it?

• A good summer nectar plant for bumblebees, which can reach deep into the flowers with their long tongues.
• The nutlets are food for seed-eating birds such as finches.
• A fast pioneer of clearings and disturbed ground, covering the soil until perennials take over.
• Beautiful, patterned two-lipped flowers that are worth looking at closely with a hand lens.
• Easy to weed where it is not wanted: it is shallow-rooted and has no runners.

Common hemp-nettle: where does it grow best?

• In the wild in arable fields, clearings, woodland edges, ditch banks, tall-herb vegetation and damp woods.
• Sun to partial shade; it likes a woodland edge.
• Moist, rich soil, preferably slightly acid: sand, loam or peat.
• It needs bare or disturbed ground to germinate; in dense vegetation it disappears within a few years.

Goes well with

• Foxglove: Grows on the same acid soil of woodland edges and clearings, and is also a bumblebee plant.
• Rosebay willowherb: Another pioneer of clearings, with pink spikes for bees and butterflies.
• Hedge woundwort: A perennial mint-family plant of woodland edges, with dark purple flowers for bumblebees.
• Common comfrey: Flowers on the same moist soil and also attracts lots of bumblebees.

Common hemp-nettle: when and how to plant it?

1. Planting is rarely needed: hemp-nettle often appears by itself on disturbed ground.
2. If you want to sow it, buy seed from a wildflower nursery or take seed from your own garden; never dig up plants from the wild.
3. Sow outdoors in September–October on loosened soil: the seed needs a cold winter to germinate in spring.
4. Scatter thinly, rake in lightly and firm. Leave 25–30 cm between plants.
5. No watering is needed, except for seedlings in a dry spring.

Care

Watering

Not needed; on dry soil it stays small.

Feeding

Not needed: it already grows vigorously on rich soil.

Spreading

In fields and vegetable plots it can come up in masses. Hoe or pull young plants before they flower and mulch the soil.

Letting it seed

To keep it in a wild corner, leave a few plants standing until September so the seed can ripen.

Gloves

The stiff hairs and spiny calyces scratch: wear gloves when weeding.

Tip: To keep hemp-nettle in the garden but out of your vegetable beds, let it set seed only in a wild corner at the edge and hoe the rest off before it flowers.

Pruning and mowing

When: Not needed: it is an annual. In the vegetable plot, weed from May to July, before the nutlets ripen.

How:

• Pull up unwanted plants before they set seed; they are shallow-rooted.
• In a wild corner, leave the dead stems until spring: birds search them for seed and insects use them for shelter.
• Weeded plants without ripe seed can go on the compost heap.

Pruning calendar and basic rules

Propagation

Seed

It spreads only by seed. The nutlets drop from the calyx in late summer, overwinter in the soil and germinate in spring. Some stay viable for a few years.

Common hemp-nettle: how does it get through the winter?

Hardy to −10 °C: protect in harsh winters.

• The plant dies in autumn; the species overwinters as seed in the soil.
• The dry stems with empty calyces stay standing for a long time and shelter small insects.
• The seed needs winter cold to germinate in spring.

Diseases and pests

• Too many plants: Can form a dense stand in a field or vegetable plot. Hoe early in spring, weed before flowering and mulch the soil.
• Spiny calyces: They prick when you weed or pick. Wear gloves.
• Mistaken for nettle: Children sometimes avoid it needlessly; it does not sting, but the hairs do scratch.
• Aphids: Sometimes aphids on the shoot tips. Leave them: ladybirds and hoverflies will clear them up.

Through the year

• March: Seedlings appear on bare soil.
• April: Weed in the vegetable plot where it is not wanted.
• May: Growth. Hoe off young plants before they flower.
• June: Start of flowering.
• July: Full flower: bumblebees on the flowers.
• August: Flowering and seed set.
• September: Last flowers. Sow on loosened soil.
• October: Sowing is still possible. Leave dead stems for birds and insects.

Did you know?

• The name Galeopsis comes from the Greek galè, ‘weasel’, and opsis, ‘appearance’: the flower was thought to resemble a weasel’s face.
• In 1930 the Swedish botanist Arne Müntzing recreated this species by crossing two other hemp-nettles. It was one of the first times a wild plant species had been made experimentally.
• The two hollow bumps at the base of the lower lip are typical of hemp-nettles and help you recognise the genus.