Propagating Lagarosiphon major (Curly Waterweed)

Propagating the African oxygenator Lagarosiphon major by cuttings and fragments — and why this banned, invasive weed must never reach open water.

Overview

Lagarosiphon major — African elodea, curly waterweed or oxygen weed — is a monocotic aquatic plant native to southern Africa. It is a robust freshwater oxygenator with densely packed, curly leaves carried along long stems, and it tolerates cool to temperate water better than most tropical stem plants.

Lagarosiphon is dioecious, with male and female flowers on separate plants, and leaves are borne in an alternate, sub-opposite or whorled arrangement depending on the species. In cultivation and in its invasive range it reproduces vegetatively rather than by seed, which makes propagation trivial and escape catastrophic.

Propagation Method

Curly waterweed propagates by fragmentation and stem cuttings. A detached piece of stem will continue growing and root on its own, so the plant multiplies from any broken-off segment. There is no need for seed, flowering, or special technique.

Step-by-Step

1. Select a strong, leafy stem and cut a section 10–15 cm long with sharp scissors.
2. Trim away leaves from the lowest few centimetres of the cutting.
3. Push the bare base into the substrate, or weight a bundle down so it stays put.
4. Roots emerge from the lower nodes and anchor the new plant.
5. Once growth resumes, the cutting behaves as an independent plant.
6. Capture and bag every loose fragment — even a small piece can establish.

Conditions for Healthy Growth

This is a cool-water species, comfortable from roughly 12 to 24 °C, at pH 6–8 and across soft to hard water. It grows well under medium lighting without added CO2, which suits unheated or temperate setups. Its cold tolerance is precisely what lets it overwinter and dominate in cooler climates where it has invaded.

Trimming & Maintenance

Trim about every week to ten days, topping stems before they crowd the surface. Replant healthy tops and discard tired lower portions. Because the brittle stems shed fragments freely, always net the clippings out immediately and never rinse trimmings down a drain.

Common Challenges

Day to day, the practical challenges are its vigorous, fragment-prone growth in cool water. Both are controlled by frequent trimming and meticulous collection of every loose piece.