Onion Plant

This is a true bulb plant, not a rhizome or tuber, and it behaves like a submerged lily. Crinum thaianum comes from Thailand, where it grows in slow-moving streams and shallow ponds. The bulb can reach the size of a small onion — hence the common name — and the leaves extend as long, wavy ribbons that can exceed one metre in a large tank.

The leaves are dark green, soft, and slightly curled along the edges, growing directly from the bulb in a dense cluster. Unlike many rosette plants, the bulb must not be fully buried — the top third should be exposed above the substrate to prevent rot. A nutrient-rich substrate helps, and root tabs near the bulb provide steady feeding.

It is one of the easier large aquarium plants. Moderate light, temperatures from 22 to 29 °C, and pH 5.5 to 8 cover its range without special demands. CO₂ injection is not needed but produces noticeably longer and healthier leaves. The main challenge is space: in a 200-litre tank or smaller the plant quickly dominates, shading everything beneath it.

The plant goes through rest periods where growth stops and some leaves yellow and die off. This is normal and the bulb sends out new leaves after several weeks. Propagation is by bulb offsets — small bulbs form at the base of the parent and can be separated once they have their own roots. It also flowers above the surface, producing white, lily-like blooms.