Mare’s-tail

Mare’s-tail: how do you recognise it?

Habit

Straight, unbranched stems standing 20–40 cm above the water; a clump grows to about 50 cm across and keeps spreading.

Leaves

Narrow and linear, 1–3 cm long, in whorls of 6–12 around the stem; underwater they are longer, limper and paler green.

Flowers

Tiny greenish flowers without petals in the leaf axils; they are hardly noticeable.

Rhizome

Creeps through the mud and keeps sending up new stems.

Pond zone

Shallow to deeper water: 10–50 cm below the water surface.

Plants: April–June · Pruning: August and October

Why grow it?

• A distinctive, architectural shape: straight stems with whorls of leaves, like a stand of miniature pines in the water.
• Works as an oxygenator: the submerged stems take up nutrients and so hold back algae.
• Native: it belongs in Belgian ditches and ponds and fits perfectly in a wildlife pond.
• Dragonfly larvae climb the straight stems out of the water to emerge as adults, and small aquatic creatures shelter among them.
• Bridges the gap between shallow and deeper water, from 10 to 50 cm.

Mare’s-tail: where does it grow best?

• Full sun: in shade the stems become limp and few of them reach above the water.
• Clear, still or slow-moving water, neutral to lime-rich; it does poorly in acid water.
• Planting depth 10–50 cm; in shallow water most stems emerge, in deeper water it grows mainly submerged.
• An aquatic basket with heavy soil: loam or clay, perhaps with a little peat, with no potting compost or fertiliser.
• Allow about 50 cm per basket.

Light

Sun

Soil type

Loam, clay or peat

Acidity

Neutral or chalky

Moisture

Wet

Size

0.4 m tall, 0.5 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Water lily: Round floating leaves as a contrast to the straight stems, in deeper water.
• Frogbit: A small floating plant that shades the water between the stems.
• Flowering rush: Pink flower heads in summer, in the same shallow zone.
• Water plantain: Broad leaves and airy white flower sprays beside the fine foliage.

Mare’s-tail: when and how to plant it?

Plant in April–June.

1. Plant from April to June, once the water has warmed and growth is under way.
2. Use a sturdy aquatic basket at least 30 cm across and fill it with heavy garden soil or aquatic compost.
3. Lay the rhizomes horizontally, 3–5 cm deep, with the stems pointing up, and firm the soil well.
4. Top with a 2–3 cm layer of gravel so the soil does not wash out and fish do not disturb it.
5. Lower the basket carefully to a depth of 10–50 cm; if you like, start shallower and lower it as the stems grow.
6. Leave about 50 cm between baskets.

Care

Water level

Top up with rainwater in dry spells; if the basket dries out, the stems wither.

Feeding

Never: it gets enough nutrients from the water and soil, and extra fertiliser only feeds algae.

Thinning

It spreads by rhizomes. In August, cut away stems and rhizomes growing outside the basket.

Autumn

In October, cut dead stems back to just above the water so less material rots in the pond.

Repotting

Every three or four years in May, lift it from the basket, divide it and replant in fresh soil.

Tip: Stand the basket in a sunny spot in shallow water, around 10–20 cm deep: that is where most of the ‘little pines’ rise above the surface and the plant stays compact.

Mare’s-tail: when to prune it?

Pruning months: August and October.

When: Thin out in August and clear away dead stems in October.

How:

• In August, use a sharp knife or secateurs to cut away stems and rhizomes growing outside the basket.
• In October, cut brown, dead stems back to just above the water surface.
• Leave some of the old stems standing: overwintering aquatic creatures shelter among them.
• Leave cut material on the bank for a day so small creatures can crawl back into the pond.

Caution: Put thinnings on the compost heap, never into a ditch or pond in the wild.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In May, lift the clump from the basket, cut the rhizome into 10–15 cm pieces each with a few stems, and plant them in new baskets.

Rhizome pieces

In summer you can detach a piece of rhizome with a few stems and push it into a basket of heavy soil; it roots readily.

Mare’s-tail: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: it overwinters as a rhizome in the mud.
• Above the water the stems die back in autumn; submerged stems sometimes stay green.
• No protection needed. In a small, shallow pond, move the basket to the deepest spot for the winter.
• Do not hack a hole in the ice: the shock disturbs fish and other wildlife.

Diseases and pests

• Spreading: In a small pond its rhizomes soon take over a whole zone. Keep it in a basket and cut away the runners every year.
• Limp stems: Too much shade or planted too deep: the stems stay underwater. Move the basket shallower and into more sun.
• Blanketweed: Hangs between the stems, especially in spring. Twist it out with a stick and leave it on the bank.
• Water lily aphid: Small, dark aphids on the emergent stems in summer. Hose them into the water, where fish and other creatures eat them.

Through the year

• April: Plant or divide. New stems appear.
• May: Plant. Every few years, divide and replant in fresh soil.
• June: Last month for planting. Remove blanketweed.
• July: Full growth. Top up the water level in dry spells.
• August: Thin out: cut away stems and rhizomes outside the basket.
• September: Net fallen leaves out of the pond.
• October: Cut dead stems back to just above the water; leave some standing.
• December: Resting underwater. Do not break the ice.

Did you know?

• Despite the resemblance, mare’s-tail is not related to horsetails: those are spore-bearing plants, whereas mare’s-tail is a flowering plant now placed in the plantain family.
• Each flower is greatly reduced, with a single stamen, a single ovary and no petals; the pollen is carried by the wind.
• The scientific name Hippuris comes from the Greek hippos, horse, and oura, tail.