Crinum Thaianum (Crinum thaianum) Care Guide
Bulb plant with very long ribbon-like leaves up to 1.5 m; an iconic background specimen for tall tanks.
Compiled by Aquairi from published sources · Published · Updated
Overview
Crinum thaianum is an aquatic plant in the family Amaryllidaceae. Bulb plant with very long ribbon-like leaves up to 1.5 m; an iconic background specimen for tall tanks.
Taxonomy
- Family: Amaryllidaceae
- Genus: Crinum
- Scientific name: Crinum thaianum
- Other names: Onion Plant, Thai Onion Plant
Habitat
Endemic to the coastal plain of Ranong and Phang Nga Provinces in Thailand, where it grows in flowing streams with submerged bulbs and trailing ribbon-like leaves up to 150 cm long. Listed as Endangered on the IUCN Red List.
Growth requirements
- Light: medium (≈50-80 PAR at substrate)
- CO2: optional (CO2 improves growth and coloration)
- Temperature: 22-28 °C
- pH: 6-7.5
- GH: 4-16 °dGH
- Substrate: nutrient-rich aquasoil or fertilised gravel
- Nutrient demand: medium
- Growth rate: slow
- Difficulty: beginner
Placement
- Recommended placement: background
- Maximum height: 150 cm
Propagation
Propagated vegetatively in cultivation; specific method depends on the morphological group of the plant.
Propagating Crinum thaianum (Onion Plant)
Overview
Crinum thaianum, the Thai onion plant or water onion, grows very long ribbon-like leaves up to about 150 cm from a large onion-shaped bulb. It is a slow-growing, beginner-friendly background specimen native to Thailand, where it is now listed as Endangered with only a fraction of wild populations remaining. In the aquarium it is a root feeder propagated almost entirely by daughter bulbs that form around the base of the mother bulb.
Propagation Method
Crinum thaianum reproduces through daughter bulbs, also called offsets. As the mother bulb matures it produces small bulbs around its base; once these develop their own leaves and roots they can be carefully separated and planted as new individuals. This is a slow process, so propagation rewards patience rather than frequent intervention.
Step-by-Step
- Let the mother bulb grow undisturbed until small daughter bulbs appear around its base.
- Wait until each offset has its own roots and a few leaves before separating it.
- Gently ease the offset away from the mother bulb by hand, keeping its roots intact.
- Plant the new bulb with only its lower portion in the substrate and the top of the bulb left exposed above the surface.
- If the bulb floats or won't stay put, weigh it down loosely with hardscape until roots anchor it.
- Leave the newly planted bulb undisturbed so it can establish its heavy root system.
Conditions for Healthy Growth
Provide at least medium lighting and a nutrient-rich substrate. The plant tolerates a wide range, doing well at 22–30°C, pH 6–7.5 and GH 4–16, and it even performs in outdoor ponds. Supplemental CO2 helps but is not required. Because leaves can grow extremely long, give it a tall tank where it can reach the surface.
Maintenance
As a root feeder, it benefits most from root tabs placed near the bulb. Its tough leaves resist herbivorous fish, and the plant helps oxygenate water and absorb ammonia. Trim only the oldest or damaged leaves at the base; otherwise leave it alone, as Crinum dislikes being moved once rooted.