Grass weeds don’t pick random lawns. They move into bare spots, compacted soil, thin turf, and areas with poor drainage the moment conditions favor them.
Below are the most common types of grass weeds found in Colorado lawns, along with guidance on how to identify and prevent their spread.
| Weed | Peak Season | Preferences |
| Large Crabgrass | Summer | Full sun, bare spots |
| Smooth Crabgrass | Early to mid-summer | Dry, compacted soil |
| Yellow Nutsedge | Summer | Wet soils, poor drainage |
| Purple Nutsedge | Summer | Moist, warm conditions |
| Annual Bluegrass | Fall and early spring | Partial shade, moist soil |
| Quackgrass | Spring and fall | Disturbed areas |
| Goosegrass | Late spring to summer | Compacted soil |
| Green Foxtail | Early summer | Dry, sandy, poor soil |
| Ground Ivy | Spring through fall | Shade, moist soil |
| Prostrate Spurge | Summer | Full sun, dry ground |
1. Large Crabgrass
Also called hairy crabgrass, Digitaria sanguinalis is a warm-season annual that germinates when soil temperatures reach 55°F at the 2-inch depth in late spring.
It spreads in a low, claw-like pattern with wide, distinctly hairy leaf blades and can grow up to 3 feet tall in unmowed areas.
How to prevent: Apply a pre-emergent herbicide between April 1–15 and keep turf thick to close off the bare spots where seeds establish.
2. Smooth Crabgrass
Smooth crabgrass (Digitaria ischaemum) is a separate species from large crabgrass and is frequently mistaken for it.
The key difference is in the leaf surface: smooth crabgrass has hairless leaf blades and sheaths, a shorter and finer texture overall, and tends to lie lower to the ground.
It shares the same warm-season annual life cycle and the same preference for thin, sun-exposed turf.
How to prevent: The same pre-emergent herbicide window that controls large crabgrass is effective here. Reducing compaction along pavement edges, where smooth crabgrass clusters most often, also helps.
3. Yellow Nutsedge
Yellow nutsedge (Cyperus esculentus) is a perennial sedge, not a true grass. Roll the stem between two fingers, and you’ll feel it’s triangular rather than round.
Its bright yellowish-green color stands out against the surrounding turf, and it noticeably outgrows lawn grass between mowings in summer.
It spreads through underground tubers that can remain dormant in soil for multiple years and re-sprout repeatedly after treatment.
How to prevent: Standard grass herbicides have no effect. Products containing halosulfuron or sulfentrazone, applied while plants are still young, are the only reliable control option.
4. Purple Nutsedge
Purple nutsedge (Cyperus rotundus) is closely related to yellow nutsedge and identified the same way, by its triangular stem and three-ranked leaf blades.
The seed heads are purplish-brown rather than yellow, and it tends to appear in warmer, wetter conditions.
It is generally considered more aggressive and harder to control than yellow nutsedge, and is one of the most invasive weed species globally.
How to prevent: The same sedge-specific herbicide products apply, though consistent treatment across multiple growing seasons is typically required to see lasting results.
5. Annual Bluegrass
Annual bluegrass (Poa annua) is a winter annual with fine-textured, light green leaf blades.
It germinates in fall when soil temperatures drop below 70°F, survives through winter, produces seed heads in early spring, and dies off when summer heat arrives.
A single plant can produce hundreds to thousands of seeds that stay dormant in moist soil for years before germinating again when conditions align.
How to prevent: Fall pre-emergent herbicide applications and a dense lawn with minimal bare spots are the most effective prevention.
6. Quackgrass
Quackgrass (Elymus repens) is a cool-season perennial grassy weed that grows most aggressively in spring and fall.
Wide leaf blades, a prominent leaf sheath, and claw-like projections at the leaf base called auricles are its defining characteristics.
It spreads through underground rhizomes that re-sprout from small root fragments when disturbed, making hand-pulling counterproductive in established patches.
How to prevent: Spot-treating with a non-selective herbicide works well for isolated areas. Severe infestations often require full lawn renovation before reseeding.
7. Goosegrass
Goosegrass (Eleusine indica) is a summer annual commonly confused with crabgrass, though it grows flatter against the ground and has a distinctive silvery-white center at the base of the plant.
Compressed leaf sheaths and a habit of clustering along driveways, sidewalk edges, and other compacted areas set it apart.
It germinates slightly later than crabgrass, from late spring into early summer, and strongly prefers compacted soil.
How to prevent: Aerating to relieve compaction and applying a pre-emergent herbicide at the correct soil temperature are the most effective combination.
8. Green Foxtail
Green foxtail (Setaria viridis) is a warm-season annual recognizable by its bristly, cylindrical seed heads that appear in early summer.
It germinates in late spring and spreads quickly into thin, dry turf and bare spots with poor soil.
How to prevent: Pre-emergent herbicide applied in spring stops germination before it starts. Overseeding thin or patchy areas in fall removes the open ground this weed depends on to get established.
9. Ground Ivy
Ground ivy (Glechoma hederacea) is a broadleaf perennial in the mint family, not a grassy weed, but one of the most persistent lawn invaders in shaded, moist areas.
Its square stems, round scalloped leaves, and small purple flowers in spring make it identifiable.
It spreads by creeping stems that root wherever they contact soil, forming a dense mat that crowds out grass.
How to prevent: Triclopyr-based herbicides applied in fall, when the plant is pulling nutrients into its root system, give the most consistent results. Improving drainage and light penetration addresses what keeps it coming back.
10. Prostrate Spurge
Prostrate spurge (Euphorbia maculata) is a summer annual broadleaf weed that grows flat against the soil from a central taproot, spreading outward under full sun in dry, compacted conditions.
Small oval leaves, often with a reddish spot in the center, and a milky white sap released when stems are broken are its clearest identifying features.
How to prevent: Pre-emergent herbicide in spring and overseeding thin turf areas close off the bare ground it needs to take hold.
If you’re finding it difficult to identify a particular type of grass weed, CSU Extension’s weed database covers Colorado-specific species with photos and control guidance.
Common Questions About Grass Weeds
What’s the difference between grassy weeds and broadleaf weeds?
Grassy weeds have narrow leaf blades with parallel veins and closely resemble lawn grass, which is what makes them hard to spot early. Broadleaf weeds like ground ivy and prostrate spurge have wider leaves with branching veins and are usually more visible.
When should I use pre-emergent versus post-emergent herbicide?
Pre-emergent herbicides prevent weed seeds from germinating and need to be applied before soil temperatures trigger germination, which is why spring timing matters so much. Post-emergent herbicides treat actively growing weeds and work best on young plants before they’ve matured or set seed heads.
Will nutsedge come back after treatment?
That happens often, unfortunately. Applications that kill the visible plant frequently miss the underground tubers, which can re-sprout in subsequent seasons. Reliable control requires well-timed treatments with sedge-specific products across multiple growing seasons.
Your Weekends Are Worth More Than This
Managing these weeds consistently is easier when it fits into a regular maintenance routine rather than becoming a seasonal emergency.
If you’re trying to build a realistic budget around professional lawn care, our guide on landscape maintenance costs in Colorado breaks down what to expect by service level and property size.
Easy Green Landscaping handles weed control as part of a complete landscape maintenance plan built around your property in Centennial, Littleton, Parker, Englewood, and the wider Denver metro area.
Call us at (303) 766-3304 or message us here, and we’ll put together a plan that keeps your lawn in good shape season after season.