Propagating Greater Duckweed (Spirodela polyrhiza)

How to propagate Spirodela polyrhiza, the multi-rooted greater duckweed: floating fronds bud daughters and form winter turions, doubling fast and needing regular thinning.

Overview

Spirodela polyrhiza, the greater duckweed, is a floating plant whose smooth round flat fronds are 0.5 to 1.0 cm wide. Each frond carries several minute roots and a dark red underside, with the upper surface mostly green. It forms dense colonies that mat across freshwater surfaces and is valued for shade and nutrient export.

Propagation Method

Greater duckweed reproduces vegetatively through frond budding during spring and summer; flowering is rare. New daughter fronds form on and separate from parent fronds. For overwintering it also produces turions, dense dormant buds storing more than 60% starch, which sink and later germinate when water warms.

Step-by-Step

Skim a small group of healthy multi-rooted fronds from an established mat.
Float them on still freshwater so the roots dangle freely below.
Provide medium light and a little dissolved nutrient; parent fronds bud new daughters within days.
Let the colony spread, then divide off a portion of fronds to seed new containers.
If turions form and sink, they will germinate on their own once water reaches about 15 C.

Conditions for Healthy Growth

Temperature 18-28 C; turions germinate near 15 C as water warms.
Medium surface lighting.
Calm, still freshwater for a stable mat.
Low nutrient demand; excels at taking up excess nutrients.
No CO2 supplementation required.

Maintenance

Thin the mat roughly weekly by netting out excess fronds so light reaches submerged plants and the colony stays in its vegetative growth phase. In cooler conditions expect a natural dormancy as turions sink in fall and regrowth resumes in spring.