Water Pimpernel

Where most aquarium plants demand soft, acidic water, Samolus valerandi does the reverse — thriving in hard, alkaline conditions while holding a low rosette of spoon-shaped leaves.

Samolus valerandi is a marginal plant found naturally in marshes and along stream banks across much of the world. It grows submerged in aquariums but keeps the same compact rosette form, sending up a flower stalk with small white flowers when it breaks the surface. It is one of the few foreground or midground plants that thrive in water with a dKH above 7 and pH up to 9.

Temperature between 22 and 26 °C with moderate light keeps it growing at a slow, steady pace. CO₂ injection is optional — the plant grows without it but remains more compact and greener with supplementation at 5 to 40 mg/l. In hard water it can be prone to calcium deposits on older leaves; wiping them during water changes keeps the plant looking clean.

Propagation is by cuttings or separating daughter plants from the mother rosette. It grows emersed readily on moist substrate and is winter hardy in temperate climates, making it suitable for pond margins as well as aquariums.