Propagating Najas Grass / Guppy Grass (Najas guadalupensis)

Najas grass propagates effortlessly by fragmentation — any broken piece grows. A rootless, fast bushy plant that floats or anchors loosely, ideal for fry and shrimp.

Overview

Najas grass (Najas guadalupensis), widely sold as guppy grass, is a submerged plant with a slender, branching stem reaching up to 60–90 centimeters. Its thin, somewhat transparent, flexible leaves are up to 3 centimeters long and just 1–2 millimeters wide, edged with minute teeth. Native to the Americas, it is a popular beginner aquarium plant prized for its hardiness and growth rate, and it provides excellent shelter for fish.

The stems produce closely spaced tufts of short, narrow leaves that interlock, forming a dense mass nearly impenetrable by adult fish — which is why it is a favorite for breeding setups and fry protection.

Propagation Method

Najas grass propagates by simple fragmentation. Its branches break apart and propagate quite easily, so any broken piece will continue to grow into a new plant. No cutting technique, hormone, or rooting medium is needed — fragmentation is the plant's natural and dominant mode of spread in the aquarium.

Step-by-Step

1. Take or break off any healthy portion of the bushy stem — length is not critical.
2. Either let the fragment float at the surface as a free-floating mass, or tuck it loosely into the substrate.
3. Provide low to moderate light; the plant grows quickly even in modest conditions.
4. Leave the fragment undisturbed and it will branch and bush out on its own.
5. Thin the resulting mass periodically to produce more fragments for new tanks.

Conditions for Healthy Growth

Najas grass thrives submerged in ponds, ditches, and streams in the wild, and is undemanding in the aquarium. It grows well as a giant floating mass or planted in substrate, tolerates low light, and is an extremely fast nutrient consumer — making it useful during tank cycling and for keeping nutrients in check.

Trimming & Maintenance

Maintenance is mostly about controlling its speed: pull out or trim back excess growth before it shades the whole tank. Every removed handful is a ready-made propagation batch. Because the branches break apart easily, the plant is harder to ship and is not ideal for high-flow tanks, where it can disintegrate.

Common Challenges

The main challenges are its fragility and speed. Strong flow snaps the brittle stems into countless drifting fragments, and its rapid growth can quickly fill a tank if left unchecked. Keep it away from powerful filter outlets and thin it regularly.