Duckweed on the Surface:

Duckweed (Lemna minor and Spirodela polyrhiza) is a free-floating plant found in near-stagnant freshwater habitats and is found across most of the world. Each thallus is a small green disc, 1 to 8 mm in diameter in Lemna minor and 5 to 10 mm in diameter in Spirodela polyrhiza, with roots that create habitat in the water below. In the Botanical Method Aquarium, it forms a surface layer that provides cover to our fishes and helps to absorb excess nutrients in the water column.

Essential Details

• Care Level: Easy
• Growth Habit: Fast, forms a continuous surface layer
• Light: Medium
• CO2: Not Necessary
• Propagation: Division
• Tint Tolerance: Low to High
• Habitat Location: Still and slow-moving freshwaters, nearly worldwide, including native North American populations
• Optimal For: Betta fish, shrimp, fry, and other small species suited to surface cover and biofilm grazing in blackwater and biotope aquariums
• Use with Caution: Rinse before introducing; may carry beneficial hitchhiking snails or snail eggs from the grow-out ponds
• Size Range: Lemna minor thalli 1 to 8 mm long with a single root of 1 to 2 cm; Spirodela polyrhiza thalli 5 to 10 mm wide with several roots
• Quantities: One 4 oz cup portion, about the size of a ping pong ball; a mix of both species will be included

Duckweed for Planted Aquariums & Blackwater Biotopes

Duckweed grows best as a continuous layer, or mat, of plants in near-stagnant water. Because floating thalli draw on atmospheric CO2 and sit in full light, duckweed absorbs excess nutrients from the water column readily. Biofilms can form on the roots and the underside of the thalli, providing supplemental nutrition to shrimp, fry, and microfauna such as copepods and ostracods, and giving them a grazing surface at the top of the aquarium. This supplemental nutrition helps to provide sustenance between our regular fish feedings.

When growing aquarium plants, we often take into account the amount of tint in the water column as more tint can reduce photosynthesis rates in our plants. However, this has little impact on duckweed as it's a floating plant. It is easy to grow in both dark, tannin-stained water or in low-tint aquatic environments. The important factor is the light intensity provided from your aquarium light.

Under favorable conditions, duckweed can double its biomass in about two days, so be wary if you have plants growing beneath as complete cover limits the light and gas exchange available in the water column. We recommend thinning by hand as it fills in, keeping part of the surface clear. We compost excess duckweed and never release aquarium plants into local ponds, ditches, or waterways.

Beneath the Leaves: Lemna minor and Spirodela polyrhiza in the Wild

Lemna minor and Spirodela polyrhiza grow in near-stagnant wetlands and the slow margins of streams, where dense mats can cover the water surface. These mats are an important food source for the fish and waterfowl that share the habitat of our favorite fishes. Lemna minor is found on nearly every continent, and it moves between waters when its sticky roots cling to the plumage and feet of birds.

Spirodela polyrhiza also marks the seasons. In autumn the thalli die back and the plant often overwinters as a turion, a dense winter bud that sinks and remains dormant until the water reaches 15°C (59°F). Each new Spirodela polyrhiza mat begins from an overwintered turion.

Where a botanical contributes as it breaks down, an aquatic plant is living and contributes as it grows. So let them grow. Mother Nature leads the way.

Sustainability Note:

Please select a heat/cold pack if necessary. Check your local weather before ordering to avoid any shipment holds or cancellations. All Plants may contain snails or snail eggs. We keep them in all of our aquariums for the benefits they provide. Our blackwater aquarium plants are provided in cooperation with PNW Bettas in adherence to their Shipping and DOA Policies. Your curated selection will arrive in their packaging separate from your botanical, wood & merch orders.