Summer Grass
Digitaria sanguinalis
Summer grass is a fast-spreading annual grass weed that invades lawns and gardens over the warmer months, dying off after frost.
Summer grass is a low-growing annual grass with a sprawling, tufted habit. Stems often bend and root at the lower nodes before spreading outward, giving established plants a flattened, star-shaped or crab-like appearance from above - hence the common name crab grass. Leaves are pale to mid-green, flat and slightly hairy, tapering to a point, and the seed heads carry several finger-like spikes radiating from a single point at the top of the stem, typically 3 to 13 spikes per head. Mature plants can reach 30 to 90cm where unmown, though in regularly cut lawns they stay low and spreading.
As a seedling, summer grass emerges from soil with narrow, pale green blades and a distinctive fringe of fine hairs at the collar (where leaf meets stem), which helps distinguish it from desirable turf grasses at an early stage. The root system is fibrous and shallow, making young plants relatively easy to pull, though established mats are far more difficult to remove by hand.
This weed germinates from seed once soil temperatures warm in spring, and it grows vigorously through summer, setting seed prolifically before dying back with the first frosts of autumn or winter. It is common across most of Australia in lawns, garden beds, disturbed soil, footpath edges and cultivated areas, and thrives in warm, moist conditions with good sunlight.
Management relies on preventing seed set and disrupting the germination cycle. Maintaining a dense, healthy lawn through correct mowing height, fertility and irrigation reduces the bare or thin patches summer grass exploits. Hand removal of isolated plants before seed heads form is effective in garden beds. In turf, pre-emergent control ahead of the spring germination window and targeted post-emergent control of young seedlings are the main chemical strategies; mature, seeded plants are much harder to manage effectively.
How to identify
Look for these signs of a summer grass infestation:
- Patchy, coarse-textured lawn: summer grass has a lighter green, coarser leaf than most turf species, creating uneven patches that stand out, especially as turf grasses slow down in cooler weather while summer grass is still actively growing.
- Flattened, spreading clumps: plants form low, star-shaped mats with stems rooting at the nodes, most noticeable in thin or bare areas, along edges, and in garden beds.
- Finger-like seed heads: from mid to late summer, look for thin, radiating spike clusters at the top of upright stems - a reliable identifying feature.
- Seasonal die-off: the whole plant turns brown and dies with the first frosts, leaving dead patches and bare ground that new seed will fill the following spring.
Field check: pull back a section of the suspect grass - summer grass has a shallow, fibrous root system and often shows hairy leaf collars where the blade meets the stem, unlike smooth-collared turf grasses.
Lookalikes: summer grass is often confused with winter grass (Poa annua), but winter grass is a cool-season weed that germinates in autumn and seeds in winter/spring, with a more upright, tufted growth habit and whitish seed heads rather than finger-like spikes. It can also resemble couch or other creeping turf grasses when mown low, but the pale, hairy leaf collar and radiating seed head distinguish it once it's allowed to grow past mowing height.
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