Family: Poaceae

Status:

Description:
A smallish tufted grass, usually under 30cm high, which grows best in moist soils. Leaves blades are flat, bright green, to 8mm wide. The leaves are strongly scented of coumarin, a sweet smell unlike the usual "green" smell of most grass. Walking through a stand of sweet vernal grass may stir up enough of the smell to be detectable, or sniff the crushed leaves. The seed heads are dense, although becoming more open during flowering, green to begin with but ripening to pale brown.

Preferred habitat and impacts:
Usually found in ungrazed pasture and on road verges, tolerating a range of conditions but most invasive in moist soils in sunny or semi-shaded sites. It may disappear in dry years, and become abundant in wet years.
A weed of remnant grassy native vegetation in farming areas, where it can suppress native groundcover species. It tolerates infertile soils.

Dispersal:
The seed is spread in mud on machinery and vehicles, and can adhere to animals and clothing. Wind and water may also spread seed. This plant may be sold by herb nurseries as "vanilla grass". Don't buy it, as it is very invasive.

Look-alikes:
In their final straw-coloured form the seed heads are similar to those of another weed, Yorkshire fog grass (Holcus lanatus). This grass also has similar soft textured broad flat leaves, but they are greyish, and velvety hairy.
A native species, scented holygrass (Hierochloe rariflora) also smells of coumarin when crushed but its open branched growth habit and seed heads, and forest habitat, distinguish it from sweet vernal grass.

Control:
Isolated plants should be removed before they seed, or if they have already begun to produce seed, then bagged for careful disposal. Spraying with grass selective herbicides will kill large infestations, though blanket removal of grass cover may be inadvisable, as it is likely to be replaced with more weeds. Fire may help manage sweet vernal grass populations, particularly the use of a hot fire in spring, when the plant is preparing to flower.