Repotting guide

When & how to repot Ivy-leaved Duckweed (Lemna trisulca)

Also called Ivy-leaved Duckweed, Star Duckweed.

More about ivy-leaved duckweed

About Ivy-leaved Duckweed

Lemna trisulca · also called Ivy-leaved Duckweed, Star Duckweed · flowering

Ivy-leaved Duckweed is a distinctive submerged duckweed native to Europe, Asia, and North America, forming translucent pale-green fronds connected in branching chains beneath the water surface. Unlike other duckweeds, it stays submerged until flowering. An excellent oxygenator and fish food plant for wildlife ponds and aquaria. Hardy and low-maintenance.

Mature size: Individual fronds 5–15 mm long; colonies spread indefinitely through the water column; generally thinner, less invasive canopy than common Lemna minor.

How to tell ivy-leaved duckweed needs repotting

Repotting on a calendar is less reliable than reading the plant. For ivy-leaved duckweed, watch for these signs:

Roots spiralling thickly out of the drainage holes or pushing the whole plant up out of the pot.
The pot is so packed that water runs straight through in seconds and barely wets the soil.
It has split a plastic pot, or the rootball is a solid mass with almost no soil left when you slide it out.
Growth and (for ivy-leaved duckweed) flowering have clearly stalled despite good light and feeding — but remember this plant likes being snug, so a little crowding alone is not a reason to repot.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot ivy-leaved duckweed

Only every 2–4 years, when genuinely crowded. Ivy-leaved Duckweed is one of the plants that genuinely prefers a snug pot — it grows and flowers better with its roots a little restricted, so resist the urge to repot it on schedule. Submerged, free-floating aquatic perennial; fronds ovate-lanceolate 5–15 mm, linked in branching colonies resembling ivy; rootlets hanging freely in water..

What size pot to step ivy-leaved duckweed up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Ivy-leaved Duckweed positively prefers a snug pot: it flowers and grows better when the roots are a little restricted. The single biggest repotting mistake here is over-potting — dropping ivy-leaved duckweed into a pot two or three sizes up. All that surplus soil holds water the small root system cannot use, stays cold and wet, and rots the roots within weeks. When in doubt, choose the smaller pot.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot ivy-leaved duckweed

Early spring, just as new growth restarts, is the ideal window for ivy-leaved duckweed. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting ivy-leaved duckweed

Confirm it actually needs it. Slide ivy-leaved duckweed out and check the roots. Only continue if it is genuinely packed — this plant prefers a snug pot, so if there is still soil and room, put it straight back.
Pick a pot only one size up. Choose a pot just 2–3 cm wider with good drainage. Resist anything bigger; over-potting is the main killer here.
Ease it out gently. Water lightly the day before, then tip ivy-leaved duckweed out, supporting the base. Tease the outer roots free only enough to stop them circling.
Repot at the same depth. Add a layer of fresh free-floating — no substrate required, set the plant so the soil line sits exactly where it did before, and backfill around the sides, firming lightly.
Settle it in. Water once to settle the soil, then let it sit. Hold off on more water until the top of the soil dries — fresh soil around a small root system stays wet for a while.

Aftercare

Because the new soil holds more water than the old crammed rootball did, ease right back on watering — let the top of the soil dry before you water ivy-leaved duckweed again, or you will rot the roots in the very pot you just moved it to. Keep it out of harsh direct sun for a fortnight. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for ivy-leaved duckweed

Ivy-leaved Duckweed wants free-floating — no substrate required. Lemna trisulca is a free-floating aquatic with rootlets that hang in the water column absorbing nutrients directly. No sediment or substrate needed. Grows in ponds, lakes, aquaria, and slow streams. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting ivy-leaved duckweed — frequently asked questions

How often should you repot ivy-leaved duckweed?

Only every 2–4 years, when genuinely crowded for ivy-leaved duckweed. Only repot ivy-leaved duckweed every 2–4 years, and only when it is genuinely root-bound — it flowers and grows best slightly crowded. Step up just one pot size in spring using free-floating — no substrate required. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does ivy-leaved duckweed need?

When is the best time of year to repot ivy-leaved duckweed?

Does ivy-leaved duckweed like to be root-bound?

Yes — ivy-leaved duckweed genuinely flowers and grows best when slightly pot-bound, so do not rush to repot it. The mistake to avoid is over-potting into a much larger pot: the excess soil stays wet, the roots cannot use it, and the plant rots. Only repot every few years and only one snug size up.

Should you fertilise ivy-leaved duckweed after repotting?

Not immediately. Wait about 4 weeks after repotting ivy-leaved duckweed. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.