Repotting guide

When & how to repot Cryptocoryne undulata (Cryptocoryne undulata)

Also called undulate Crypt, wavy Cryptocoryne.

More about cryptocoryne undulata

About Cryptocoryne undulata

Cryptocoryne undulata · also called undulate Crypt, wavy Cryptocoryne · tropical

Cryptocoryne undulata is a Sri Lankan water trumpet with narrow, wavy-edged brownish-green leaves forming a 10-25 cm midground rosette. Hardy and adaptable to varied water chemistry and low light, it spreads by runners into a textured stand. A reliable Crypt for community planted tanks, prone to the usual post-transplant melt before it rebounds.

Mature size: 10-25 cm tall and 15-25 cm wide submerged, spreading wider over time.

Watch for — Nutrient deficiency: Pale, weak leaves in inert gravel; add root tabs and chelated iron.

How to tell cryptocoryne undulata needs repotting

Repotting on a calendar is less reliable than reading the plant. For cryptocoryne undulata, 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 cryptocoryne undulata) 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 cryptocoryne undulata

Only every 2–4 years, when genuinely crowded. Cryptocoryne undulata 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. Low-to-medium clumping rosette spreading by runners into a textured midground stand..

What size pot to step cryptocoryne undulata up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Cryptocoryne undulata 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 cryptocoryne undulata 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 cryptocoryne undulata

Early spring, just as new growth restarts, is the ideal window for cryptocoryne undulata. 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 cryptocoryne undulata

Confirm it actually needs it. Slide cryptocoryne undulata 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 cryptocoryne undulata 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 nutrient-rich aquarium substrate, 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 cryptocoryne undulata 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 cryptocoryne undulata

Cryptocoryne undulata wants nutrient-rich aquarium substrate. Root feeder preferring a nutrient-rich substrate or gravel/sand with root tabs. Plant the roots into the substrate, keeping the crown and growing point at the surface. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting cryptocoryne undulata — frequently asked questions

How often should you repot cryptocoryne undulata?

Only every 2–4 years, when genuinely crowded for cryptocoryne undulata. Only repot cryptocoryne undulata 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 nutrient-rich aquarium substrate. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does cryptocoryne undulata need?

When is the best time of year to repot cryptocoryne undulata?

Does cryptocoryne undulata like to be root-bound?

Yes — cryptocoryne undulata 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 cryptocoryne undulata after repotting?

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