Water Poppy Facts, Care, Planting, & Hardiness (Hydrocleys nymphoides)
Water poppies, Hydrocleys nymphoides, are a low-maintenance, perennial aquatic plant. Their species name, nymphoides, references their similar appearance to water lilies in the genus Nymphaea.
Delicate tri-petal yellow flowers with a purple center make water poppies easily identifiable. Their shiny, floating leaves are approximately 5 to 10cm (2-4″), and flowers have a diameter of around 5cm (2″).
Water poppies are a favorite of several species of bees, including honeybees and bumblebees (Apis mellifera and Bombus brevivillus, respectively), which makes them a great choice to aid in the conservation of these essential, but struggling, hard-working insects.
Water poppies have stolons—often called runners, which are stems that grow just below the surface and either break off or extend outward to establish new colonies. Originally found in the subtropics of Central and South America, water poppies were introduced to the wetlands of the United States, South Africa, Australia, and New Zealand as a byproduct of pond and aquarium cultivation.
Water Poppy Growth & Hardiness Considerations
Water poppies can grow up to 30cm (12″) tall, but much of their size comes from horizontal spread, with plants reaching up to 1.5 meters. Water poppies flower June through August in water temperatures of at least 21°C (70°F). Although each flower only lasts one day, an abundance of flowers per cluster ensures their beauty continues all summer.
Water poppies grow quickly in direct sunlight and warm weather. However, they are rather hardy and can be grown in regions with extreme minimum winter temperatures of around -4°C (25°F) and up (USDA zones 9-11). Water poppies tolerate temperate climates, but indoor overwintering in shallow tubs is recommended for cooler areas.
How to Plant Water Poppies:
Water poppies should be planted in rich soil along pond margins or in shallow fresh water (pH 6.5-7.5). They prefer less than 15cm (6″) of water but can survive in depths up to 40cm (16″). Water poppies should be planted on pond bottoms in containers or wet loam—a fertile mud composed of equal parts sand, silt, and clay. If using a container, the bottom two-thirds should be filled with special aquatic soil (not lightweight potting mix) and the roots spread out over top. More aquatic soil should then be added so the base of the stem is in around 2.5cm (1″) of soil. If planted in pond margins, water poppies will grow outward onto the water’s surface with floating stems.
Water poppies do not produce many easily harvested seeds. If planted from seeds, they should be sowed in a shallow pan in 5cm (2″) of water with aquatic soil and a top layer of sand.
How to Care for Water Poppies:
Water poppies should be cut back as needed (at least bi-annually) to avoid the plant getting weedy. Dead segments and leaves should be removed regularly. Since water poppies bloom continuously, the effort of removing dead flowers may not be worthwhile. Like many frost intolerant perennials, water poppies should be brought indoors and kept in a tub or aquarium with moist soil in direct light.
Is Water Poppy Toxic or Invasive?
Although not considered toxic, the rapid growth rate and web-like stem structure has the ability to choke streams, cause flooding, and eliminate native flora. The thick mats formed by water poppies may increase drowning risks of small animals and decrease dissolved oxygen concentrations—the amount of oxygen available to fish and other aquatic organisms.
The water poppy trade is not prohibited, but certain councils, such as the New Zealand Plant Conservation Network, request any wild sightings be reported. It is highly recommended that water poppies are routinely cut back and dead leaves are removed to maximize its water-cleaning benefits while minimizing its risks to other flora and fauna.
Will Fish Eat Water Poppy?
Water poppies are not considered a food source to fish or other water life, likely because of their high concentration of tannins—the bitter compounds that make red wine taste dry. Although not palatable, water poppies offer other benefits to the pond and garden ecosystem by providing organisms with shelter, shade, and protection from predators.