Frogbit

Frogbit: how do you recognise it?

Habit

Free-floating rosettes about 5 cm high that join up by runners into a loose mat, roughly 30 cm per plant.

Leaves

Round to kidney-shaped, 2–5 cm, glossy green and slightly thick; they float flat on the water.

Flowers

White flowers 2–3 cm across with three rounded petals and a yellow centre, from June to August. Male and female flowers grow on separate plants.

Roots

Long, fine roots that hang free in the water; in shallow water they sometimes root into the mud.

Winter buds

Small, firm buds at the ends of the runners that sink to the bottom in autumn.

Flowering: June–August · Plants: May–July

Why grow it?

• An easy floating plant for any pond, from a small tub to a large wildlife pond.
• The floating leaves cast shade and take up nutrients, giving algae less of a chance.
• White flowers from June to August, appearing again and again all summer.
• Native: tadpoles, young fish and small aquatic creatures shelter under the rosettes and among the roots.
• No planting needed: you simply place it on the water.

Frogbit: where does it grow best?

• Sun or partial shade, in still, sheltered water.
• Floating plant: it drifts freely on the surface; depth matters little, as long as the pond does not freeze to the bottom in winter.
• No current, fountain or waterfall: the mat breaks up or is washed away.
• The water can be acid to lime-rich; in richer water it grows faster.
• Do not let it cover more than a third of the surface, so there is enough light left for the oxygenators.

Light

Sun and partial shade

Soil type

Loam, clay or peat

Acidity

Not fussy

Moisture

Wet

Size

0.05 m tall, 0.3 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Pygmy water lily: Larger white flowers and floating leaves, in the same sunny pond or tub.
• Water violet: An underwater oxygenator that flowers above the surface in May.
• Spiked water-milfoil: Fine underwater foliage, a strong oxygenator.
• Mare’s-tail: Straight stems as a contrast to the flat, round leaves.
• Flowering rush: Pink flower heads at the edge of the pond.

Frogbit: when and how to plant it?

Plant in May–July.

1. Place the plants on the water from May to July, once it has warmed up.
2. Choose a sheltered corner, away from fountains and pumps.
3. Rinse new plants first and check them for snail eggs, duckweed and unwanted plants.
4. Start with three to five plants per square metre: they multiply quickly.
5. In a new pond, let the water settle for a few weeks before adding floating plants.

Care

Thinning

In summer, net out surplus plants once they cover more than a third of the water.

Feeding

Not needed: it takes all its nutrients from the water.

Autumn

In October, net out yellowing, dying leaves so they do not rot on the bottom.

Water level

Top up with rainwater in dry summers; if the plant is left high and dry, it dies.

Duckweed

Remove duckweed promptly: it takes up space and light between the rosettes.

Tip: Place it in a sheltered corner, away from the fountain: it grows best in still water, where the rosettes stay together nicely.

Frogbit: when to prune it?

When: Frogbit is not pruned. You simply net out the surplus in summer and clear dead leaves in autumn.

How:

• In July–August, net out surplus rosettes.
• In October, remove yellow leaves and loose plant debris from the water.
• Simply let the winter buds sink: they produce next year’s plants.
• Leave netted-out plants on the bank for a while so small creatures can get back into the water.

Pruning calendar and basic rules

Propagation

Runners

In summer, new rosettes form by themselves on the runners. Snip them off and place them elsewhere on the water.

Winter buds

In October, collect winter buds and keep them in a jar of water with a little mud in a cool, frost-free place. Return them to the pond in May.

Frogbit: how does it get through the winter?

Hardy to −25 °C.

• Hardy to about −25 °C: the plant itself dies back and the winter buds overwinter on the bottom of the pond.
• In a pond that does not freeze to the bottom, no protection is needed.
• In a tub or a very shallow pond, keep a handful of winter buds in a jar of water with a little mud, cool and frost-free, and put them back in May.
• The new plants appear only late in spring, when the water warms up: be patient.

Diseases and pests

• Water lily aphid: Small, dark aphids on the leaves in summer. Hose them into the water, where fish and other creatures eat them.
• Snails: Pond snails sometimes nibble small holes in the leaves. It is usually minor; remove large numbers by hand.
• Gone after winter: The winter buds froze in a shallow tub or were removed with the silt. Next time, keep a few buds indoors.
• Mat too dense: A closed leaf cover robs the oxygenators of light. Thin out regularly.

Through the year

• April: Winter buds gradually rise as the weather warms.
• May: Place plants on the water. Return stored winter buds.
• June: Flowering begins. Runners form new rosettes.
• July: In flower. Net out the surplus if more than a third is covered.
• August: In flower. Top up with rainwater in dry spells.
• September: Winter buds form at the ends of the runners.
• October: Clear yellow leaves. Collect winter buds for a tub.
• December: Resting: the winter buds lie on the bottom.

Did you know?

• Morsus-ranae is Latin for ‘bite of the frog’, just like its Dutch name.
• In North America, where it was introduced in the 20th century, frogbit has become a troublesome invasive plant.
• Male and female flowers grow on separate plants and seed is rarely set: it spreads mainly by runners and winter buds.