Star grass: the bushy, fast-growing green filler

A fast grower from the Americas

Heteranthera zosterifolia — star grass or stargrass — is a South American stem plant in the pickerelweed family (Pontederiaceae). In the wild it grows in and beside slow fresh water, and it produces small pale-blue flowers when it reaches the surface and grows emersed. In the aquarium it is grown for its fast, bushy submersed form rather than its flowers.

Leaves set like stars

The plant carries narrow, light-green leaves arranged around the stem so that, viewed end-on, each node looks like a little star — hence the name. Stems branch freely, so a few planted shoots quickly knit into a soft, feathery mass. The colour is a fresh, bright green that sits well against darker or red-leaved neighbours.

Easy, but give it light

Star grass is genuinely easy on water chemistry and does not need CO₂, but it has one real requirement: enough light. In dim tanks it tends to stretch, with long gaps between nodes and thin lower growth; under medium to high light it stays compact and bushy. It is a fast grower and a hungry water-column feeder, so keep the water fed — it will happily mop up excess nutrients. CO₂ is optional but makes it noticeably denser and quicker.

Parameter	Value
Lighting	Medium to high; low light makes it leggy
CO2	Not required; denser and faster with it
Temperature	20–28°C
pH	5.5–7.5
Hardness	Soft to moderately hard
Fertiliser	A hungry water-column feeder
Substrate	Any; not fussy about roots
Growth rate	Fast
Placement	Midground to background
Difficulty	Easy

A soft green cloud

Star grass shines as a midground-to-background filler, forming a soft cloud that blurs the line between hardscape and open water. Because it branches and fills so readily, it is a good choice for greening a new layout quickly, and its fine texture contrasts nicely with broad-leaved plants such as anubias or with red stems. Trim the tops to encourage side shoots and a denser bush.

Trim and replant

Propagate by cutting side shoots or tops and replanting them; they root quickly and grow away without fuss. Frequent trimming both multiplies the plant and keeps it compact, since topping pushes it to branch lower down. As with most fast stems, replanting healthy tops and discarding tired bases gives the best-looking group over time.

Legginess and lower thinning

Leggy, stretched growth is the usual complaint and most often means the light is too low for it, though shading by taller plants contributes — raise the light or move it up the layout. Thin, bare lower stems follow from the same shading, plus age; regular topping and replanting keeps the base furnished. Melt or leaf drop soon after planting is typically the emersed-to-submersed transition and usually passes once new submersed leaves form.

More plants in this series

• Water wisteria — another fast bushy stem
• Rotala rotundifolia — fast stem, warmer tones
• Dwarf hygro — undemanding fast stem
• Asian ambulia — feathery fast background stem