Onion Grass (Romulea spp).

Onion Grass is known as Guildford Grass. Guildford Grass is a small perennial herb that grows from a white bulb. These are called corms. It has a yellow base and annual leaves with small pink, white, purple or yellow flowers.

Onion Weed has several shiny dark green leaves that grow from the base of the plant. If present the stem leaves are smaller.

Seed of Onion Grass is mainly spread by mowing, but it also spreads by the corms, in the intestinal tract of grazing animals, contaminated soil and by water. All this makes Onion Grass difficult to remove once it establishes.

After you finish reading this, you will be able to:

  • Identify Onion Grass, Guildford Grass or Onion Weed.
  • Know what conditions favour Onion Grass.
  • Know the best cultural and chemical options to control Onion Weed.


More information on common lawn weeds is in our weed ID chart. Onion Grass indicates low soil P. For more about what weeds reveal about soil conditions see our blog on indicator weeds.


How to Identify Onion Grass.

Category: Perennial herb.

Flower: The flowers are 2-3 cm in width and are small pink, white, purple or yellow. It has six petals and flowers in late winter and spring.

Height: It can grow up to 25 cm high.
Leaf length: The leaves are up to 18mm in length.

Reproduction: Every year the corm renews, and Guildford Grass reproduces by seed and corm. Flowers develop in the second year and the seedbank persists for up to 5 years. This weed needs warm temperatures to germinate, and so favours bare ground. Although a perennial it behaves like an annual and dies back at the end of the Summer.

Habitat: Guildford Grass is a common weed of lawn, pasture, and sports fields.

Guildford Grass flowering


How to remove Onion Grass from your lawn.

You can best control Guildford Grass with herbicides.


Cultural control.

Physical removal is difficult as the corms occur to a depth of 200 mm. Mowing is not effective to control this weed.

You can dig or pull out small populations of Guildford Grass. If hand-pulling, be careful to remove the entire corm and any corms, as any left behind will resprout. This process has to be ongoing for several years to make sure that you remove all the remaining seeds and corms.

Chemical control.

The sulfonylurea herbicide, Iodosulfuron controls Onion Grass. This is contained in the product ProForce Duke 100WG from Indigo Specialty Products