Dwarf Hairgrass

Scientific name: Eleocharis parvula (sold as E. pusilla by some nurseries)

Origin: found on several continents

Growth: medium, 3–10 cm

Light and CO2: low to medium; CO2 helps

Placement: foreground lawn

Propagation: runners

Dwarf Hairgrass (Eleocharis parvula) looks like a fine lawn grass and behaves like one. It grows 3–10 cm tall and spreads by runners, horizontal shoots that travel just under the substrate and send up new tufts beside the parent, until the pinches you planted join into a carpet. It is found on several continents and is not fussy about water. Tropica rates its light and CO2 needs as low, while Aquarium Co-op recommends medium to high light for a tight carpet; under weak light it tends to grow taller and thinner rather than dense. Nursery stock is grown with the leaves in air, so a new pot often browns and melts back as it converts to underwater growth. Leave the roots in place and fresh green blades come up within a few weeks. Plant it in small pinches a couple of centimetres apart rather than one clump. A full carpet from a few pots takes patience rather than skill. The fine blades trap food and biofilm, the microbial film shrimp graze, and give shrimplets somewhere to hide at ground level.

Water: adaptable to ordinary tropical conditions and a range of hardness.

Planting: remove the rock wool, split the pot into small pinches and push each into the substrate with tweezers so the roots are buried and the blades free. Space pinches a few centimetres apart. Root tabs (fertiliser capsules pushed into the substrate) or a nutrient-rich substrate help it settle.

Light and feeding: medium light gives the tightest lawn; it survives lower. CO2 injection (carbon dioxide gas added to boost growth) is not required but speeds carpeting. Trim the whole carpet with curved scissors like mowing a lawn.