Repotting guide

When & how to repot Hygrophila polysperma (Hygrophila polysperma)

Also called dwarf hygro, Indian swampweed.

More about hygrophila polysperma

About Hygrophila polysperma

Hygrophila polysperma · also called dwarf hygro, Indian swampweed · tropical

Hygrophila polysperma, dwarf hygro, is one of the fastest, hardiest stem plants in the aquarium hobby, with light-green oval leaves on upright stems. It tolerates low light, a wide temperature range and neglect, making it ideal for beginners. Note it is a federally listed noxious weed in the US and must never be released into waterways.

Mature size: Stems to 30-50 cm tall; spreads indefinitely if untrimmed

Watch for — Leggy, sparse stems: In low light stems stretch with bare lower portions; increase light or trim and replant tops to keep growth compact and bushy.

How to tell hygrophila polysperma needs repotting

Repotting on a calendar is less reliable than reading the plant. For hygrophila polysperma, watch for these signs:

Roots poking out of the drainage holes or coiling visibly around the inside of the pot.
You are watering far more often than you used to because the rootball dries out within a day or two.
Water runs straight through and out the bottom without soaking in.
Top growth has slowed or new hygrophila polysperma leaves are noticeably smaller than older ones despite good light.

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 hygrophila polysperma

Every 12–18 months — sooner if roots show fast. Hygrophila polysperma's growth habit — fast-growing erect stem plant with opposite oval leaves; trims and replants easily, quickly forming a dense background or midground hedge. — sets the pace. Hygrophila polysperma, dwarf hygro, is one of the fastest, hardiest stem plants in the aquarium hobby, with light-green oval leaves on upright stems. It tolerates low light, a wide temperature range and neglect, making it ideal for beginners. Note it is a federally listed noxious weed in the US and must never be released into waterways.

What size pot to step hygrophila polysperma up to

Step up one pot size — about 2–3 cm (an inch) wider. Hygrophila polysperma grows fast, so it will fill that space within a season, but jumping several sizes at once still backfires: the unused soil stays soggy and rots even a vigorous root system. One size at a time, every year or so, is the rhythm.

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 hygrophila polysperma

Early spring, just as new growth restarts, is the ideal window for hygrophila polysperma. 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 hygrophila polysperma

Time it for spring. Repot hygrophila polysperma in early spring as growth restarts so it re-roots quickly into the fresh soil.
Choose one size up. Pick a pot about 2–3 cm wider with drainage holes. One step only — a much bigger pot stays soggy and rots roots.
Ease the plant out. Water lightly the day before, then tip hygrophila polysperma out and gently loosen any roots circling the bottom of the rootball.
Repot at the same depth. Put a layer of fresh nutrient aquarium substrate (rooted stem plant) in the new pot, set the plant so its soil line is unchanged, and backfill, firming lightly.
Water and pause feeding. Water once to settle the soil. Hold off fertiliser for about a month — fresh mix already has nutrients and feeding now burns new roots.

Aftercare

Water hygrophila polysperma once to settle the soil, then let the surface dry before watering again — fresh mix around the roots stays wetter than the old compacted ball, so the commonest post-repot mistake is overwatering. Keep it out of direct sun for a week or two while roots re-establish. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for hygrophila polysperma

Hygrophila polysperma wants nutrient aquarium substrate (rooted stem plant). Plant stems in fine gravel or aquasoil where they root readily; also grows floating or emersed in marginal mud. A nutrient-rich substrate boosts the already vigorous growth. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting hygrophila polysperma — frequently asked questions

How often should you repot hygrophila polysperma?

Every 12–18 months — sooner if roots show fast for hygrophila polysperma. Repot hygrophila polysperma roughly every 12–18 months, in early spring as growth restarts. It grows fast and circles its pot quickly, so step up one size (about 2–3 cm wider) into fresh nutrient aquarium substrate (rooted stem plant). Don't jump several sizes — that soggy excess soil is what rots vigorous roots.

What size pot does hygrophila polysperma need?

When is the best time of year to repot hygrophila polysperma?

Can you put hygrophila polysperma straight into a much bigger pot?

No. Even a fast-growing hygrophila polysperma should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.

Should you fertilise hygrophila polysperma after repotting?

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