Source: Wikimedia Commons
Water hyssop
BeginnerBacopa monnieri
A tough, bright green stem plant (Japanese name Otomeazena) with small, thick leaves that widen toward the tip, in opposite pairs. A staple that tolerates almost any water and grows without CO2; emersed it bears pale pink to white flowers.
About
Water hyssop (Bacopa monnieri, Plantaginaceae), called Otomeazena in Japan, is a perennial found throughout the tropics and subtropics on the banks of lakes, rivers and ponds, including slightly saline coastal sites. In Japan it has been reported as naturalised in Okinawa. Depending on water level and season it ranges from a creeping emersed form to an upright submersed one. The thick, bright green leaves are about 0.8–2 cm long, oblanceolate (widest near the rounded tip). The related Bacopa caroliniana has larger, lemon-scented leaves. Emersed plants bear pale pink to white flowers in the leaf axils. Several forms exist, with rounder or clearly toothed leaves, and a compact, self-branching form ('Compacta') has been sold under another plant's name. It is one of the oldest and least demanding aquarium stem plants: with enough light it grows in almost any water, though too little light makes the lower stems rot. CO2 is optional. It grows easily emersed in moist soil, and in the warm season it can trail flowering stems over the edge of an outdoor pot. It is widely available from specialist shops and pet shops in Japan.
Source: Wikipedia (CC BY-SA 4.0)
Size of the Water hyssop
The Water hyssop grows to Small stem plant with leaves 0.8–2 cm long.
Temperature & humidity for the Water hyssop
The ideal temperature for the Water hyssop is 18〜28℃.
Basic Info
Origin
Tropics and subtropics worldwide
Lifespan
Perennial; maintained by replanting cuttings
Size
Small stem plant with leaves 0.8–2 cm long
Temperature
18〜28℃
Watering & Fertilizer
CO2 and fertiliser optional
Growing Tips
Lighting
Needs at least medium light; in too little light the lower stems rot.
CO2 & Fertilizer
CO2 is optional. With CO2 and strong light, keep up nitrate, phosphate and iron.
Water Temperature & Quality
Optimum 18–28°C; tolerates pH 5–9 and hard water.
Substrate & Attachment
Plant in small groups in the mid- or background.
Trimming & Propagation
Propagate from side shoots or stems arising from the base.
Cautions
It has been reported as naturalised in Okinawa. Never release plants into the wild or let them escape from tanks or outdoor pots.
Water hyssop FAQ
QWhat is the growing difficulty level for Water hyssop?
Beginner. A variety suitable for beginners. No special equipment or experience is required—you can grow it without problems by setting up a basic cultivation environment.
QWhat is the ideal temperature for Water hyssop?
The ideal temperature for Water hyssop is 18〜28℃. Avoid sudden temperature changes and maintain a stable environment.
QHow large does Water hyssop get?
The mature size of Water hyssop is Small stem plant with leaves 0.8–2 cm long. This may vary slightly depending on cultivation environment and individual differences.
QHow should I water and fertilize Water hyssop?
Water hyssop: watering & fertilizer — CO2 and fertiliser optional. Aim for appropriate frequency and amount.
QWhat is the typical price for Water hyssop?
The price of Water hyssop varies significantly by variety, characteristics, size, and lineage. Please check GrowerDirect's price guide for the latest market information.
Last updated: September 23, 2026
References & Sources
Edited & verified by: GrowerDirect Editorial Team
The classifications, regulations, and growing data on this page are created and verified based on the primary information database below.
Taxonomy & Authority
Regulations & Conservation Status
Not listed in CITES (no match in Species+). Not regulated under Japan's Invasive Alien Species Act or Species Conservation Act. It is not on the Ministry of the Environment's alien species list (2nd ed., September 2026), though the related B. rotundifolia is a Control Consideration species, and it has been reported as naturalised in Okinawa. Never dump aquatic plants into rivers, ponds or ditches, or flush them away with tank water. Drain unwanted plants and trimmings and dispose of them as household waste.
Sources: Species+ (CITES listing check) / Ministry of the Environment: list of Invasive Alien Species (Invasive Alien Species Act) / Ministry of the Environment: alien species list, plants (2nd ed.)
Regulations may change. Always verify the latest information with the relevant authorities.
Related Species
Find listings for this species
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