Great horsetail

How to recognise it

Habit

Perennial plant without flowers, with upright stems rising from a deep, creeping rhizome; forms large colonies.

Stem

Sterile stems 0.5–1.5 m tall and up to 2 cm thick, ivory white and smooth, with a dense whorl of thin green branches at every node.

Leaf

The true leaves are fused into sheaths around the nodes, with 20–40 narrow brown teeth. The green of the plant is in the branches.

Spores

In March–April separate, unbranched, pale brownish-white fertile stems of 15–40 cm appear, each with a cone of 4–8 cm. They wither as soon as the green spores have been shed.

Roots

Deep, dark, branching rhizomes that can creep a long way; broken pieces easily sprout again.

Confusion with

Field horsetail is much smaller, with green instead of white stems and sheaths with fewer teeth. Marsh horsetail has thin green stems, few branches and black sheath teeth with a white edge; it is poisonous to livestock.

Pruning: November

Why grow it?

• A living fossil: horsetails have existed for hundreds of millions of years and once had relatives the size of trees.
• A spectacular architectural plant for a wet, shady corner: the white stems with green whorls look like miniature fir trees.
• It indicates seepage: where it grows, lime-rich groundwater rises to the surface. Such places are often rich in unusual plants.
• The dense stands and fallen stems give shelter to amphibians and small creatures on the wet ground.
• In spring, the pale fertile stems with their cones are a remarkable sight.

Great horsetail: where does it grow best?

• In the wild: spring-fed woodland, seepages on slopes, stream banks, damp embankments and ditches, often under alder and ash.
• Wet to waterlogged, lime-rich clay or loam with moving groundwater.
• Partial shade to shade; in sun only if the soil always stays wet.
• In the garden: only suitable for a large, wet wildlife garden, a pond edge or a small spring, preferably in a large tub or behind a root barrier.

Goes well with

• Pendulous sedge: Grows in the same seepages and offers gracefully drooping spikes as a contrast.
• Marsh marigold: Golden-yellow flowers in April, just as the fertile stems appear.
• Meadowsweet: Creamy, fragrant plumes in summer on wet soil.
• Alder: The classic tree of spring-fed woodland; it provides the partial shade the horsetail likes.

Great horsetail: when and how to plant it?

1. Think carefully: in an ordinary garden it spreads aggressively and is hard to get rid of. Choose it only for a large, wet spot.
2. Never dig it up from the wild: its sites are fragile and often lie within nature reserves. Buy a plant from a nursery for aquatic or native plants.
3. Plant in April–May in wet, limy soil, in a large sunken tub without holes or behind a root barrier reaching as deep as possible, at least 60 cm.
4. Set the rhizome 5–10 cm deep and firm the soil well.
5. Keep the soil wet throughout the first year, including summer.

Care

Watering

The soil must never dry out; at a seepage or by a pond this takes care of itself.

Feeding

Not needed: it gets everything it needs from the spring water and the soil.

Spreading

Every spring, cut off rhizomes outside the desired area with a spade and pull out new stems as soon as they appear; this gradually exhausts the rhizome.

Tidying

In autumn the stems collapse. Leave them as shelter or cut them off in November.

In a tub

Every 3–4 years, empty the tub, divide the rhizome and replant one piece in fresh, limy soil.

Tip: Plant it in a large, watertight tub sunk at the edge of your pond: you can enjoy its prehistoric look without it taking over your garden.

Pruning and mowing

Pruning months: November.

When: Not really necessary. If you want to tidy up, cut off the dead stems in November.

How:

• Cut dead stems just above the ground, or leave them as shelter for small creatures.
• To slow the plant down, keep pulling out new stems outside the desired area throughout the summer: this weakens the rhizome.
• Do not put pieces of rhizome on a damp compost heap: they can regrow.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Dividing the rhizome

In April–May, cut off a piece of rhizome with a few nodes or young shoots and plant it straight away in wet soil. This is the easiest method.

Spores

In March–April. The green spores remain viable only briefly: sow them at once on wet, bare soil under glass. Difficult and slow.

Great horsetail: how does it get through the winter?

Hardy to −25 °C.

• The green stems die back in autumn and collapse; the plant overwinters as a rhizome deep in the soil.
• Fully hardy, to about −25 °C.
• The fallen stems form a sheltered litter layer for small creatures.
• In March the pale fertile stems are the first to appear, before the green stems.

Diseases and pests

• Spreading: The main problem in a garden: the rhizomes creep far and deep. Plant in a tub or behind a barrier and remove runners straight away.
• Drought: In dry soil it stays small and turns yellow. It really needs a wet spot.
• Harmful to livestock: Horsetails can be harmful to grazing animals, especially horses, if large amounts end up in hay or pasture. Keep them out of hay meadows and grazing land.
• Confusion with field horsetail: Field horsetail is a persistent weed in vegetable gardens. Look at the stems: great horsetail has thick white stems, field horsetail thin green ones.

Through the year

• March: The pale fertile stems with cones emerge.
• April: Spores are released. Then the white stems appear. Plant or divide.
• May: Full growth. Cut off runners outside the area.
• June: At its best. Keep the soil wet.
• July: Water the pond edge in dry weather. Pull out spreading stems.
• August: Check for runners.
• October: The stems discolour and collapse.
• November: Cut off dead stems or leave them as shelter.
• December: Resting underground.

Did you know?

• Horsetails are related to the tree-sized plants that formed the coal forests about 300 million years ago. Belgium’s coal also formed from those forests.
• Each spore carries four ribbon-like arms that uncoil in dry weather and coil up again when damp: they help the spores drift away.
• Telmateia comes from the Greek telma, meaning marsh or mud: it likes to have its feet wet.