Creeping primrose-willow

Ludwigia repens is one of the most widely kept red aquarium plants and one of the easiest to grow. Native to the southern United States, Central America, and the Caribbean, it grows along the edges of ditches, rivers, and ponds, often forming dense trailing mats. In the aquarium it reaches about 30 cm in height and is best suited to the midground or background, where its reddish leaves contrast with green plants. Unlike many red species, L. repens will grow under moderate light of around 0.4 watts per litre and does not require CO2 injection to stay healthy. Stronger light deepens the red colour and encourages more compact growth, while lower light produces greener, more upright stems. The plant is highly polymorphic in nature and hybridises easily with other Ludwigia species, so there is variation among commercially available forms. Propagation is as simple as cutting a stem and re-planting it; the original stem left in the substrate will branch freely. Regular trimming keeps the plant bushy and prevents it from reaching the water surface, where it begins to grow horizontally. An ideal choice for beginners who want a splash of red without the high-light or CO2 demands that most red plants require.