TankBud

Water onion

Crinum thaianum

Also known as Thai onion plant, Onion plant, Giant onion plant, Water lily onion

FreshwaterBulb / tuberBulb offsets

Water onion (Crinum thaianum)
(c) Utain Pummarin, some rights reserved (CC BY) · cc-by

Care at a glance

Light
Low light
CO2
No CO₂ needed
Temperature
72–82°F
22–28°C
Max height
39.4 in
100 cm
Growth rate
Medium
Placement
Background
Type
Bulb / tuber
pH
6.0–8.0
Hardness
4–18 dGH
Spread
11.8 in (30 cm)
Nutrient uptake
Root feeder
Growth region
Submersed or emersed
Difficulty
Easy
Family
Amaryllidaceae
Origin
Southern Thailand (endemic)

Overview

Water onion is a big, forgiving bulb plant for large tanks and a rugged background or specimen plant. It is rated easy.

Did you know

Wild water onion is now protected in Thailand after river dredging wiped out most of its natural range. It is listed as Endangered on the IUCN Red List, one of the few common aquarium plants that is endangered in the wild.

Caring for water onion

Plant water onion with only the lower third of its bulb buried, so the bulb does not rot. Give it a rich substrate and plenty of room in a large tank.

It is a root feeder, so a rich substrate or root tabs keep it strong. It needs no CO2 and gets by in low light, and it tolerates a wide range of light and temperature swings. Keep it at 72 to 82°F (22 to 28°C).

It grows steadily rather than fast and can reach about 39 in (100 cm). Mature plants can reach the surface and grow emersed. The bulb forms offsets you can separate and plant on their own. Herbivorous fish and cichlids usually leave its fibrous leaves alone.

Good to know

Water onion is a bulbous species in the amaryllis family, Amaryllidaceae, so it is a true bulb rather than a stem or rosette plant. Its tough, ribbon-like leaves can reach 1.5 meters or more in the wild while staying only a couple of centimeters wide. Mature bulbs can flower, carrying fragrant, lily-like white blooms to the water surface.

In the wild

Water onion is endemic to a handful of coastal-plain rivers and streams in southern peninsular Thailand. It grows as an emergent bulb rooted in the bed, with long ribbon leaves streaming in the flow. Habitat loss and over-collection have also hit the wild population, though it remains widely cultivated for the hobby.

Common questions

Does water onion need to be planted in the substrate?

Yes, but only partly. Push the roots into the substrate and leave at least the top half of the bulb uncovered so it doesn't rot.

Does water onion need CO2?

No. Water onion grows well without added CO2 and suits a low-tech tank.

How much light does water onion need?

Water onion is a low-light plant, and the light that comes with a standard tank kit is enough for it.

Does water onion need root tabs?

Yes. Water onion draws much of its food through its roots. Push root tabs in near it, or grow it in a nutrient-rich soil.

How do you propagate water onion?

Water onion propagates by bulb offsets. The bulb forms offsets, which can be separated and planted on their own.

How tall does water onion grow?

Water onion grows to about 39.4 in (100 cm) tall. It grows at a moderate pace.

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