Propagating Hydrocotyle Japan (Hydrocotyle sibthorpioides)

How to propagate Hydrocotyle Japan by dividing its creeping runners and replanting them, plus the high light it needs to stay low and carpet the foreground.

Overview

Hydrocotyle sibthorpioides is a low, spreading plant with rounded, peltate leaves often described as egg-shaped, each carrying five to seven shallow lobes and measuring roughly 0.5 to 2 cm across. In nature it creeps along the ground, even between sidewalk cracks, which is exactly the habit that makes the 'Japan' form a popular delicate emerald-green foreground carpet in the aquarium.

It is a fast, weed-like grower. Under medium light without CO2 it still spreads, but it grows much faster and stays denser with stronger lighting, so most aquarists treat it as a beginner-friendly carpeting plant that simply needs enough light to behave.

Propagation Method

Hydrocotyle Japan is propagated vegetatively, by cuttings taken from its creeping stems and runners rather than from seed. Because the plant naturally spreads sideways, the easiest method is to divide the established creeping mat: separate a section of runner that already carries leaves and roots, then replant it elsewhere to start a new patch.

Step-by-Step

Wait until the creeping mat has filled in and runners are trailing across the substrate.
Choose a healthy runner segment that carries several leaves and visible roots.
Pinch or snip the runner to free a section, keeping stem, leaves and roots intact.
Plant the segment into nutrient-rich substrate in the new spot, pressing the runner down so it stays in contact with the bottom.
Give it bright light and let it root and spread to form a fresh carpet.

Conditions for Healthy Growth

Lighting: medium light works, but bright light keeps it low and carpeting; in the wild it wants full sunlight for complete growth.
CO2: not required, though added CO2 speeds growth and helps it carpet.
Substrate: nutrient-rich substrate supports the fast turnover of leaves.
Water: tolerant of a wide range, roughly 18-28 C, pH 6-7.5, GH 3-14.
Temperament: emersed-capable and adaptable, which is why it readily naturalises outside its range.

Maintenance

Even with plenty of light this plant tends to reach upward, so regular trimming is unavoidable if you want to keep it as a tight foreground. Trim the canopy roughly every three weeks, removing tall or shaded growth, and replant the healthiest cut runners to thicken thin areas.

Common Challenges

Reaching upward: in strong light the plant can still stretch for the surface, so it needs trimming to stay flat.
Stunted or dying leaves: very high light without matching nutrients or CO2 can stunt or burn back leaves, while the same plant looks full in slightly calmer light.
Spreading too far: its weed-like vigour means it will creep into neighbouring plants unless you trim and divide it regularly.