Rough horsetail

Rough horsetail: how do you recognise it?

Habit

Dense groups of upright, unbranched stems 0.5–1 m tall.

Stems

Hollow, jointed and ridged, dark green and rough with silica; evergreen.

Nodes

At each node a tight-fitting sheath with a black and a grey-white ring.

Spores

Some stems carry a small, pointed, cone-shaped spore head at the tip. Horsetails do not flower.

Roots

Deep, far-creeping rhizomes, by which it spreads strongly.

Plants: March–May and September–October · Pruning: March

Why grow it?

• Ramrod-straight, evergreen stems give a crisp, graphic accent all year round.
• Handsome at the pond edge, in wet soil or in shallow water.
• Ideal in a large pot or trough on the patio, where it cannot spread.
• Green even in winter, and very decorative with frost or snow on its jointed stems.
• Tough and little work: it rarely suffers from pests or diseases.

Rough horsetail: where does it grow best?

• Sun or partial shade.
• Any soil: sand, loam, clay or peat, acid to chalky, as long as it stays moist to wet.
• At the pond edge, in wet soil or up to about 10 cm deep in the water.
• Always in a closed pot, an aquatic basket lined with dense pond fabric or behind a deeply sunk root barrier.
• Allow 40–50 cm per clump.

Light

Sun and partial shade

Soil type

Sand, loam, clay or peat

Acidity

Not fussy

Moisture

Normal or wet

Size

1 m tall, 0.5 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Marsh marigold: Yellow spring flowers at the foot of the rigid stems.
• Royal fern: A large, soft fern that contrasts with the hard lines.
• Hosta: Broad leaves beside the straight stems, in partial shade.
• Water forget-me-not: Small pale blue flowers around the base at the pond edge.
• Yellow flag: Sword-shaped leaves and yellow flowers in May–June.

Rough horsetail: when and how to plant it?

Plant in March–May and September–October.

1. Plant from March to May or in September–October.
2. Choose a large pot or tub with no holes in the bottom, or an aquatic basket lined with dense pond fabric; in a border, sink a sturdy root barrier deep into the ground.
3. Fill with ordinary garden soil, or with low-nutrient aquatic soil in the pond.
4. Plant the clump at the same depth as in its old pot and firm in well.
5. Stand the pot in the pond up to about 10 cm under water, or keep the soil in a patio pot moist at all times.
6. Water generously straight away.

Care

Water

Keep the soil moist to wet at all times. A pot on the patio often needs water in summer.

Feeding

Not needed.

Old stems

Cut brown, snapped or dried-out stems off at the base; new ones grow in by themselves.

Root barrier

Check each spring for stems appearing outside the pot or barrier, and pull them out straight away, rhizome and all.

Repotting

Repot or divide every 2–3 years: it quickly fills a pot completely.

Tip: Always plant it in a closed pot or with a deeply sunk root barrier, because it spreads aggressively. In a pot without holes at the pond edge or on the patio, the rigid stems look their best.

Rough horsetail: when to prune it?

Pruning months: March.

When: In March, before the new stems appear. Otherwise rough horsetail is hardly pruned.

How:

• Cut brown, snapped or dried-out stems right off at the base.
• Remove faded spore heads if you do not like the look of them.
• Do not shorten healthy stems: the crisp shape would be lost.

Caution: Work carefully: the stems snap easily at the nodes.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April or in September, cut off a piece of the clump with rhizome and plant it in its own closed pot.

Stem cuttings

In summer, lay pieces of stem with a few nodes in a pot of wet soil or in water; they may form roots at the nodes.

Rough horsetail: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection needed.
• The stems stay green through winter.
• In a pot on the patio: choose a frost-proof pot and do not let the soil dry out.
• In March, cut out stems snapped by snow or wind.

Diseases and pests

• Spreading: Stems pop up metres away, even under paths. Always plant with a root barrier and pull out escaped stems, rhizome and all: once it is in the border, it is very hard to get rid of.
• Brown stems: Dried-out stems in a pot that was too dry. Water more and cut them off.
• Snapped stems: Caused by wind, snow or overhanging branches. Cut them off at the base.
• Struggling in a pot: A pot full of roots gives thin, yellow stems. Repot or divide.

Through the year

• March: Cut out old and snapped stems. Plant or divide.
• April: Plant. Pull out escaped stems outside the pot.
• May: Plant. The new stems appear.
• June: Keep the soil moist. Spore heads on some stem tips.
• July: Water pots in dry spells.
• August: Water pots in dry spells.
• September: Plant or divide.
• October: Plant.
• December: Green in winter.

Edible and useful

Not edible. Rough horsetail is poisonous to grazing animals, especially horses: it contains thiaminase, which breaks down vitamin B1, so that after a while they stagger, lose weight and develop nervous symptoms; it stays harmful when dried in hay. Cattle and sheep can fall ill from it too. Do not plant it near a field or paddock, and never throw cut stems near the feed. Nor is it field horsetail: do not make tea or plant spray from it. Keep children, dogs and cats away from the hard stems. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Did you know?

• The stems are full of silica and therefore rough: in the past they were used to scour pewter and copper and to smooth wood; its Dutch name, schaafstro, means ‘planing straw’.
• In English it is also called ‘Dutch rush’, because it used to be imported from the Low Countries for scouring.
• Horsetails are an ancient group of plants: in the coal forests, some 300 million years ago, there were tree-sized relatives.