Cogon Grass

Cogon grass (Imperata cylindrica, dab) is a rhizomatous pioneer grass that covers disturbed and burnt ground fast across the Punjab plains, the KPK hills, and the Sindh coast. Young growth is grazed and the dense roots hold loose soil, so it has a place as an early coloniser. But it is also reckoned among the worst weeds in the world, and any honest account has to treat it as a plant you contain rather than encourage. On a syntropic site it is a pioneer to use with real caution, if at all.

Where it thrives

Dab is native and widespread across most tropical and subtropical regions, growing from sea level up to about 2,000 m in the Himalaya, in sub-humid to humid grasslands and open woodland.¹ It tolerates a very wide rainfall range and a spread of degraded habitats, from arable land and young plantations to roadsides and burnt clearings, which is why it turns up right across the Pakistani plains and hills.² Its edge is toughness: drought tolerance, an appetite for poor soils, and a heavy, heat-resistant rhizome network let it hold ground that many grasses cannot, and shoot and rhizome growth peak in warm conditions around 29 °C by day.²

Role in the system

On the credit side, cogon is a fast pioneer cover for bare, disturbed, and burnt ground. Its dense rhizome mat, which can run to about 1.2 m deep though it usually sits in the top 15 cm of heavy soil, grips loose material and resists both heat and breakage, so it stabilises exposed surfaces quickly.³ The young leaf carries some grazing value before it toughens, and cut green growth can be laid down as mulch. The honest framing, though, is that these uses are slight set against its vigour, and in a designed system its main practical role is the one you are trying to suppress as you bring in better cover.

Cautions

This is the species to be plain about. Cogon grass is rated among the world’s ten worst weeds, spreading aggressively through its rhizomes and forming dense stands that crowd out other plants.¹ It is a highly flammable pyrophyte that carries fire readily and then resprouts from its protected roots, so it can lock ground into a burn-and-regrow cycle that suppresses everything slower.³ As feed it is poor: silica in the leaves makes it unpalatable, and in quantity it lowers the value of a forage stand.⁴ Do not plant it deliberately into a productive system; where it is already present, the work is to shade it out and replace it.

What you get

The defensible returns are narrow: fast cover and soil-holding on bare or burnt ground, a little young-leaf grazing, mulch from cut growth, and leaf used as thatch rather than fodder in many places.⁴ Weighed against its weediness and fire-carrying habit, dab is best understood as a tough pioneer of last resort, useful for the soil it holds in the short term but managed firmly so it does not take over the very system it was meant to start.

Sources

1. IUCN Invasive Species Specialist Group. “Imperata cylindrica.” Global Invasive Species Database.
2. CABI. “Imperata cylindrica (cogon grass).” CABI Compendium.
3. EAFRINET. “Imperata cylindrica (Cogon Grass) — rhizomes and fire.” Lucidcentral.
4. Heuzé, V., et al. (Feedipedia). “Alang-alang (Imperata cylindrica).” INRAE, CIRAD, AFZ & FAO.