Repotting guide

When & how to repot Hydrocharis morsus-ranae (Hydrocharis morsus-ranae)

Also called Frogbit, Common Frogbit, European Frogbit.

More about hydrocharis morsus-ranae

About Hydrocharis morsus-ranae

Hydrocharis morsus-ranae · also called Frogbit, Common Frogbit · flowering

Frogbit is a free-floating aquatic that looks like a miniature water lily, with small kidney-shaped leaves and three-petalled white flowers in summer. It drifts on the surface of still ponds, spreading fast by runners and overwintering as sunken buds (turions). Pretty and easy in a contained pond, but invasive in parts of North America, so check local restrictions.

Mature size: Individual leaves 1-4 cm; colonies spread to cover the water surface by runners

How to tell hydrocharis morsus-ranae needs repotting

Repotting on a calendar is less reliable than reading the plant. For hydrocharis morsus-ranae, 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 hydrocharis morsus-ranae) 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 hydrocharis morsus-ranae

Only every 2–4 years, when genuinely crowded. Hydrocharis morsus-ranae 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. Free-floating perennial spreading rapidly by surface stolons into mats of small rosettes; dies back in autumn to dormant turions that sink, overwinter and resurface in spring..

What size pot to step hydrocharis morsus-ranae up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Hydrocharis morsus-ranae 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 hydrocharis morsus-ranae 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 hydrocharis morsus-ranae

Early spring, just as new growth restarts, is the ideal window for hydrocharis morsus-ranae. 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 hydrocharis morsus-ranae

Confirm it actually needs it. Slide hydrocharis morsus-ranae 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 hydrocharis morsus-ranae 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 none (free-floating), 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 hydrocharis morsus-ranae 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 hydrocharis morsus-ranae

Hydrocharis morsus-ranae wants none (free-floating). Needs no substrate; nutrients are taken directly from the water column by its trailing roots. A muddy pond bottom helps only as a nutrient reservoir. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting hydrocharis morsus-ranae — frequently asked questions

How often should you repot hydrocharis morsus-ranae?

Only every 2–4 years, when genuinely crowded for hydrocharis morsus-ranae. Only repot hydrocharis morsus-ranae 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 none (free-floating). The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does hydrocharis morsus-ranae need?

When is the best time of year to repot hydrocharis morsus-ranae?

Does hydrocharis morsus-ranae like to be root-bound?

Yes — hydrocharis morsus-ranae 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 hydrocharis morsus-ranae after repotting?

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