Arrowhead

Arrowhead: how do you recognise it?

Habit

Upright clump about 60 cm tall and 40 cm wide, which spreads a little by runners.

Leaves

Above water arrow-shaped, glossy green, on long stalks; under water it also makes ribbon-like leaves and sometimes oval floating leaves.

Flowers

White, 2–2.5 cm across, with three petals and a purple blotch at the base; in whorls of three along the stem, from June to August.

Male and female

The male flowers sit at the top of the stem, the female flowers lower down.

Tubers

In autumn it forms small tubers at the ends of runners in the mud, which carry it through winter.

Pond zone

Shallow water: 10–30 cm below the water surface.

Flowering: June–August · Plants: April–June · Pruning: October

Why grow it?

• Elegant arrow-shaped leaves: one of the finest leaf shapes at the pond edge.
• White flowers with a purple blotch, from June to August.
• The flowers attract bees, hoverflies and other insects.
• The stems and leaves are a perch for dragonflies and damselflies, and tadpoles shelter around the base.
• Less rampant than many other marginal plants: suitable for a medium-sized pond.

Arrowhead: where does it grow best?

• Sun to partial shade; it flowers best in sun.
• A rich bottom of loam, clay or peat, neutral to alkaline.
• Water depth 10–30 cm in still or slow-moving water. Planted deeper, it mostly makes submerged ribbon leaves.
• Allow about 40 cm per plant; in groups of three in a larger pond.

Light

Sun and partial shade

Soil type

Loam, clay or peat

Acidity

Neutral or chalky

Moisture

Wet

Size

0.6 m tall, 0.4 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Flowering rush: Pink flower heads at the same water depth, in the same summer months.
• Greater spearwort: Golden-yellow flowers next to the white ones, in shallow water.
• Frogbit: A small floating plant with white flowers for the open water alongside.
• Water forget-me-not: Blue flowers at the base, in the wet margin.

Arrowhead: when and how to plant it?

Plant in April–June.

1. Plant from April to June; potted plants in leaf are best put in during May–June, when they are in full growth.
2. Use an aquatic basket of 5–10 litres filled with heavy garden soil or clay, without potting compost or fertiliser.
3. Plant loose tubers about 5 cm deep; set potted plants at the same depth as in the pot.
4. Top the soil with 2–3 cm of gravel and lower the basket to 10–30 cm below the water surface.
5. Leave about 40 cm between plants.

Care

Water

Not needed in the pond. In dry summers top up the pond with rainwater so the depth stays right.

Feeding

Not needed: the pond bottom holds enough nutrients and fertiliser encourages algae.

Patience

It only comes up in May. Mark where the basket is so you do not move or damage it by mistake.

Tidying

In October remove yellowed leaves so they do not rot in the water.

Dividing

Every 2–3 years, when the basket is full, divide in May or harvest some tubers.

Tip: Mark the position of the basket in autumn: arrowhead does not come up until May, so you will not dig it up by mistake and you will know it is still alive.

Arrowhead: when to prune it?

Pruning months: October.

When: Real pruning is not needed. In October, when the leaves turn yellow, cut them off.

How:

• Cut yellowed leaves and spent flower stems off just above the water surface.
• Leave the tubers in the bottom alone: next year’s plant grows from them.
• Leave the cut material on the bank for a day so small creatures can return to the pond.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Tubers

In April–May take the tubers out of the basket or the mud and plant them one by one, 5 cm deep, in a basket of clay soil.

Division

In May, when it starts into growth, take the clump out of its basket and split it into pieces with a few leaves each.

Arrowhead: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: the tubers overwinter safely in the mud under the ice.
• The leaves die back completely in autumn; there is nothing to see above water until May.
• In a tub or mini pond: put it somewhere sheltered or lower the basket a little deeper, so the tubers do not freeze into the ice.

Diseases and pests

• Not coming up: Nothing to see in April: that is normal, it only starts in May. Wait until June before you worry.
• Only ribbon leaves: It is too deep or in flowing water. Raise the basket to 10–30 cm.
• Aphids: Small black aphids on leaves and flower stems in summer. Hose them off; fish and pond creatures eat them.
• Eaten tubers: Ducks and some fish eat the tubers or dig in the basket. A layer of gravel on the basket helps.

Through the year

• April: Plant tubers in a basket. Nothing to see above water yet.
• May: The first leaves appear. Plant or divide.
• June: First white flowers. Planting is still possible.
• July: In flower. Watch out for aphids.
• August: Last flowers. Top up the pond in dry spells.
• September: The plant forms tubers in the bottom.
• October: Cut off yellowed leaves.
• November: Dormant. The tubers overwinter in the mud.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Arrowhead makes three kinds of leaves: ribbon-like under water, oval and floating, and arrow-shaped above water. In flowing water it often keeps only the ribbon leaves.
• The species name sagittifolia means ‘with arrow-shaped leaves’, from the Latin sagitta, arrow.
• A related species is grown as a vegetable in China and Japan for its edible tubers.