Broad-leaved pondweed

Broad-leaved pondweed: how do you recognise it?

Habit

Water plant with submerged stems and floating leaves; it can spread to 1 m or more.

Leaves

Floating leaves oval to oblong, leathery, 5–12 cm long, on long stalks; sometimes also narrow, ribbon-like underwater leaves.

Flowers

Inconspicuous, greenish-brown spikes that rise above the water in summer.

Rhizome

Creeping rootstock in the mud, from which new shoots appear every year.

Water depth

Best at 50–150 cm deep; the stalks grow up to the surface.

Plants: April–June · Pruning: May and September

Why grow it?

• The floating leaves give shade and shelter to fish, tadpoles and other small water creatures.
• They cover part of the water surface and keep the water cooler and fresher.
• Dragonflies and damselflies like to rest on the floating leaves.
• A native species that belongs in a wildlife pond.
• Fully hardy and low maintenance: it comes back by itself year after year.

Broad-leaved pondweed: where does it grow best?

• Full sun to light partial shade: the floating leaves need light.
• Still to slow-moving water; no strong current, fountain or waterfall close by.
• Water depth 50–150 cm, measured from the bottom where it roots.
• A muddy or loamy bottom; in a basket: poor loam or clay aquatic compost.
• Allow 1 m or more of space: it spreads by rhizomes.

Light

Sun

Soil type

Loam, clay or peat

Acidity

Not fussy

Moisture

Wet

Size

0.05 m tall, 1 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Water lily: Other floating leaves and large flowers; plant them apart so that they do not crowd each other.
• Water violet: A submerged plant that flowers in spring and oxygenates the water.
• Hornwort: An underwater oxygenating plant and shelter for young fish.
• Flowering rush: Pink umbels in summer in the marginal zone.
• Yellow flag: Yellow flowers in May–June in the pond’s marshy margin.

Broad-leaved pondweed: when and how to plant it?

Plant in April–June.

1. Plant in April–June, when the water starts to warm up.
2. Use a pond basket at least 20 cm across, filled with poor loam or clay aquatic soil, never potting compost or garden compost.
3. Lay the rhizome horizontally in the soil with the growing tip free and cover the soil with a layer of gravel.
4. First put the basket on a brick or stone so the leaves reach the surface.
5. Lower the basket deeper as the stems grow, down to 50–150 cm.

Care

Water

Keep the pond well topped up. Replace evaporation with rainwater.

Feeding

Not needed and unwelcome: nutrient-rich water encourages algae.

Thinning

Remove excess growth so that at most half of the water surface is covered.

Dead leaves

In autumn, skim yellowing leaves and stems from the water to limit silt.

Dividing

Lift the basket every 3–4 years and divide the rhizome.

Tip: Plant it in a basket and put the basket high at first, so that the first stems reach the surface. Lower the basket only as they grow, and thin it out every year so it does not take over the whole pond.

Broad-leaved pondweed: when to prune it?

Pruning months: May and September.

When: Thin in May–June when growth gets too dense; tidy up in September.

How:

• Remove excess stems with a rake or net, or cut them below the water surface.
• In September, cut or skim off yellowing leaves and stems.
• Leave the removed material at the pond edge for a day so that small water creatures can crawl back in.

Caution: Do not throw removed pieces into ditches or natural waters: they can start growing there.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In April–June, cut off pieces of rhizome of 10–15 cm with at least one growing tip and plant them in a basket of poor loam. Put them high first and lower the basket as the stems grow.

Broad-leaved pondweed: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, down to about −30 °C, as long as the rhizome lies in the mud below the frost line. Provide a zone at least 80 cm deep.
• The floating leaves die back in autumn; the rhizome overwinters in the mud and new shoots appear in spring.
• During prolonged frost, keep a small patch of water ice-free, for example with a pond de-icer, so that gases can escape.

Diseases and pests

• Overgrowth: A carpet that is too dense lets little light through and uses up oxygen at night. Thin out in May–June.
• Aphids: On the floating leaves in summer. Wash them off with a jet of water; fish eat them too.
• Algae and blanket weed: Too many nutrients and too much light in the water. Add more plant cover, do not feed, and rake out blanket weed.
• No floating leaves: The stems do not reach the surface because the basket is too deep. Raise the basket.

Through the year

• April: Plant as soon as the water warms up. Prepare the basket.
• May: Plant and lower the basket. Thin if necessary.
• June: Plant. Thin out growth that is too dense.
• July: The floating leaves are at their best. Inconspicuous flower spikes above the water.
• August: Watch for aphids. Remove excess growth.
• September: Clear dead leaves and stems.
• October: Skim fallen leaves from the pond.
• November: Resting: the rhizome overwinters in the mud.
• December: Resting. Keep a patch of water ice-free.

Did you know?

• The name Potamogeton comes from Greek: potamos means river and geiton neighbour, so ‘river neighbour’.
• The undersides of the floating leaves often carry pond snails, eggs and insect larvae.
• Ducks and other waterfowl eat the fruits of pondweeds.