Repotting guide

When & how to repot Eleocharis parvula (Eleocharis parvula)

Also called dwarf spikerush, mini hairgrass.

More about eleocharis parvula

About Eleocharis parvula

Eleocharis parvula · also called dwarf spikerush, mini hairgrass · tropical

Dwarf spikerush, or mini hairgrass, is the shortest carpeting hairgrass for aquariums, forming an extremely low, fine green lawn that spreads by runners. Grown submerged under good light and CO2 it creates a tight, manicured foreground that rarely needs trimming. It is a favourite for nature-style aquascapes wanting a short, dense grass carpet.

Mature size: Blades 3-10 cm tall; spreads by runners to form a carpet

Watch for — Slow carpeting: Low light, CO2 or substrate nutrients. Boost light and CO2 and add root tabs to speed runner spread.

How to tell eleocharis parvula needs repotting

Repotting on a calendar is less reliable than reading the plant. For eleocharis parvula, 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 eleocharis parvula 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 eleocharis parvula

Every 12–18 months — sooner if roots show fast. Eleocharis parvula's growth habit — very low carpeting grass spreading by fine horizontal runners into a short, dense turf. naturally stays shorter than e. acicularis, so it seldom needs cutting. — sets the pace. Dwarf spikerush, or mini hairgrass, is the shortest carpeting hairgrass for aquariums, forming an extremely low, fine green lawn that spreads by runners. Grown submerged under good light and CO2 it creates a tight, manicured foreground that rarely needs trimming. It is a favourite for nature-style aquascapes wanting a short, dense grass carpet.

What size pot to step eleocharis parvula up to

Step up one pot size — about 2–3 cm (an inch) wider. Eleocharis parvula 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 eleocharis parvula

Early spring, just as new growth restarts, is the ideal window for eleocharis parvula. 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 eleocharis parvula

Time it for spring. Repot eleocharis parvula 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 eleocharis parvula out and gently loosen any roots circling the bottom of the rootball.
Repot at the same depth. Put a layer of fresh nutrient-rich planted-tank substrate 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 eleocharis parvula 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 eleocharis parvula

Eleocharis parvula wants nutrient-rich planted-tank substrate. Plant tiny portions a couple of centimetres apart in aquasoil or fine sand/gravel with root tabs. Fine, fertile substrate helps the delicate runners knit together quickly. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting eleocharis parvula — frequently asked questions

How often should you repot eleocharis parvula?

Every 12–18 months — sooner if roots show fast for eleocharis parvula. Repot eleocharis parvula 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-rich planted-tank substrate. Don't jump several sizes — that soggy excess soil is what rots vigorous roots.

What size pot does eleocharis parvula need?

When is the best time of year to repot eleocharis parvula?

Can you put eleocharis parvula straight into a much bigger pot?

No. Even a fast-growing eleocharis parvula 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 eleocharis parvula after repotting?

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