Hemp agrimony

Hemp agrimony: how do you recognise it?

Habit

Dense clump of upright, often reddish stems, 1–1.5 m tall and about 80 cm across.

Leaves

Opposite, divided into three to five lance-shaped, toothed segments, like hemp; slightly hairy.

Flower

Small, dusky pink to lilac flower heads in broad, flat to domed clusters, from July to September.

Seed

Small nutlets with a white tuft that are carried by the wind; this is why it self-seeds so easily.

Roots

Short, woody rootstock; the clump slowly widens.

Flowering: July–September · Plants: March–April and September–October · Pruning: March, May and September

Why grow it?

• One of the best native butterfly plants for late summer.
• Bees, bumblebees and hoverflies also find plenty of nectar.
• Long flowering from July to September, when many other wild flowers are over.
• It grows where many plants struggle: wet soil, pond edges and partial shade.
• Tall and sturdy: a fine backdrop for a natural border or waterside planting.
• The faded stems give insects shelter in winter.

Hemp agrimony: where does it grow best?

• Sun or partial shade; it flowers best and draws most butterflies in sun.
• Moist to wet, fertile soil: loam, clay or peat. Acid, neutral and chalky are all fine.
• Ideal beside a pond or ditch or in a damp corner; in an ordinary border it does well if the soil does not dry out.
• It grows tall and wide: put it at the back and leave 60–80 cm between plants.

Light

Sun and partial shade

Soil type

Loam, clay or peat

Acidity

Not fussy

Moisture

Normal or wet

Size

1.5 m tall, 0.8 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Purple loosestrife: Purple spikes in the same wet soil and in the same months.
• Meadowsweet: Creamy, scented plumes in the same damp spot, a little earlier in summer.
• Yellow loosestrife: Yellow flowers next to the pink, also native and good for bees.
• Wild angelica: Large white umbels in late summer, also a magnet for insects.
• Common valerian: Pinkish-white, scented heads in June–July, before the hemp agrimony flowers.

Hemp agrimony: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or in September–October.
2. Dig a hole twice as wide as the root ball and mix in some compost, unless the soil is already rich.
3. Plant at the same depth as in the pot and firm the soil well.
4. Leave 60–80 cm between plants.
5. Give a good can of water straight away and keep the soil moist for the first few weeks.
6. A layer of leaf mould around the base keeps the soil cool and moist.

Care

Water

Not needed in a wet spot; in a border, water during long dry spells.

Feeding

Usually not needed; on poor soil, a little compost in spring.

Deadheading

Cut off the flower clusters in September, before the seed ripens, if you do not want seedlings.

Support

In a windy spot or rich soil the stems may flop; cutting back in late May makes the plant sturdier.

Dividing

Dividing every 3–4 years keeps the clump young and compact.

Tip: If you do not want seedlings all over the garden, cut off the flower clusters in September as soon as they fade: by then the butterflies will have had their fill.

Hemp agrimony: when to prune it?

Pruning months: March, May and September.

When: Cut the dead stems down in March, just before new growth starts. In September, remove the faded clusters if you do not want seedlings; in late May you can shorten the stems for a lower plant.

How:

• In March, cut all old stems down to about 10 cm above the ground.
• Leave the stems standing all winter: insects shelter in them and they look lovely with frost.
• In late May you can cut the stems back by a third: the plant stays lower, branches more and flowers a little later.
• In September, cut off the faded flower clusters before the fluffy seed appears.

Caution: Do not throw the clippings into a field with grazing animals or near hay: even dried plant parts are poisonous.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April or in October, lift the clump and cut it into pieces with a spade, each with a few buds. Replant straight away and water in.

Seed

It self-seeds: move the seedlings in spring. You can also sow fresh seed in a pot in autumn and leave it outside.

Cuttings

In April–May, take cuttings of young shoots 8–10 cm long and insert them in moist cutting compost under plastic, in good light but out of direct sun.

Hemp agrimony: how does it get through the winter?

Hardy to −35 °C.

• Very hardy, to about −35 °C: no protection needed.
• The top growth dies back in autumn; the rootstock regrows in spring.
• Leave the stems until March as winter shelter for insects.
• In a large pot it stays hardy; in severe frost, stand the pot against a wall and do not let it dry out.

Diseases and pests

• Seedlings everywhere: It self-seeds freely. Cut off the flower clusters after flowering or choose the double form ‘Flore Pleno’.
• Flopping: Tall stems fall over after wind or rain. Cut back by a third in late May or give support.
• Aphids: On the shoot tips in spring. Ladybirds usually deal with them; otherwise hose them off.
• Powdery mildew: White powder on the leaves at the end of a dry summer. Water during drought and cut off affected leaves.
• Limp leaves: Drooping leaves in a spot that is too dry. Water, or move the plant somewhere moister.

Through the year

• March: Cut old stems down to 10 cm. Plant or divide.
• April: Plant. New shoots appear. Take cuttings.
• May: In late May, shorten by a third if you like.
• July: First flowers. Butterflies on the blooms.
• August: Full flower. Water during dry spells.
• September: Last flowers. Cut off faded clusters before the seed ripens.
• October: Plant or divide.
• December: Resting. Leave the stems as winter shelter.

Edible and useful

Not edible. These plants contain pyrrolizidine alkaloids, like the common ragwort along the roadsides: they damage the liver, even in small amounts taken in over a long time, and the damage is permanent. Horses and cattle are the most sensitive, also to dried plants in hay or silage, because they can no longer taste them: do not plant them in or beside a field, never throw mowings or trimmings near the feed, and do not cut them with grass for hay. Never make teas or herbal remedies from them, not even from hemp agrimony, which was once a medicinal herb. Keep children, dogs and cats away from the plant and wear gloves when cutting back. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The species name cannabinum refers to the leaves, which look like those of hemp; the two plants are not related.
• The genus name Eupatorium is said to honour Mithridates VI Eupator, king of Pontus.
• Hemp agrimony is a favourite nectar plant of the Jersey tiger, a striking day-flying moth with black-and-white forewings and red hindwings.