Onion Plant
Crinum thaianum
A tough bulb plant with long ribbon leaves, ideal for big tanks and even ponds.
| Care Difficulty | Beginner |
| Lighting | Low to Medium |
| CO2 Requirement | Not required |
| Growth Rate | Slow |
| Placement | Background |
Overview
Onion Plant (Crinum thaianum) is a tough bulb plant with long ribbon leaves, ideal for big tanks and even ponds. It is a beginner plant to grow, which makes it a great pick for beginners and low-tech tanks.
This guide explains, in plain language, how to grow Onion Plant well: what it looks like, how much light it wants, whether it needs CO2, how to plant and place it, how to make more of it for free, and the simple mistakes to avoid.
Appearance & Growth
A tough bulb plant with long ribbon leaves, ideal for big tanks and even ponds.
It is a slow grower and is normally used in the background of the aquarium. Because it grows slowly, it stays tidy and needs little trimming, though slow leaves can gather algae if the light is very strong.
Lighting
Onion Plant does best under low to medium light. Low to medium light is plenty, so a basic aquarium LED will keep it happy.
Keep the lights on a timer for about 6 to 8 hours a day. Leaving lights on longer usually grows more algae, not more plant, so add light time slowly and watch for any green film.
CO2 & Fertilising
CO2: Not required. This plant grows fine without added CO2, so it suits simple, low-tech tanks.
Feed it with an all-in-one liquid fertiliser (such as API Leaf Zone) added to the water each week, and push a root tab into the substrate near the roots, as this is a hungry root-feeder. If leaves turn yellow, get holes, or stop growing, that is almost always a lack of nutrients, not a disease.
Planting & Placement
Place the bulb on top of the substrate or only half-buried - burying the whole bulb makes it rot. Once it sprouts, the roots anchor it. Give it room as it can grow large.
How to Propagate (Make More)
It grows from a bulb. Rest the bulb on the substrate or half-bury it (never fully) and it will sprout. Mature plants may grow side bulbs or flower.
Swapping cuttings is one of the best parts of the hobby - over time a single healthy plant can fill your tank and stock a few more.
Common Problems & How to Fix Them
The most common problem is algae growing on the leaves. This usually means too much light, not enough nutrients, or weak water flow - not a problem with the plant. Lower the light a little, add fertiliser, and improve flow.
Some leaf loss right after planting is normal while the plant gets used to living underwater - keep your light, CO2 and fertiliser steady and new growth will follow. Always remove dead or rotting leaves quickly to keep the plant and water healthy.
Is Onion Plant Right for Your Tank?
Onion Plant is an easy, rewarding plant that fits almost any freshwater aquarium, including first tanks and low-tech setups. Pair it with our other plant and aquascaping guides to build a lush, healthy planted tank.