Crabgrass is a common type of grassy weed that can infest lawns and gardens. Knowing what crabgrass looks like and identifying it early is key to controlling and removing it before it spreads. There are a few characteristics that can help you recognize crabgrass.
Identifying Crabgrass By Its Growth Habit
Crabgrass is an annual warm-season grass that germinates in spring and dies with the first frost in fall. It grows quickly in summer, spreading via stems that root at nodes to form patches. There are two main species of crabgrass:
Large or Hairy Crabgrass
This species (Digitaria sanguinalis) is the more common crabgrass found in lawns. Some identifying traits:
- Grows rapidly in patches that can reach 2 feet or more in diameter
- Has hairy leaf blades and sheaths with hairs that give it a grayish or bluish cast
- Forms patches that are often reddish-purple in color as it begins to die in early fall
- Produces many tillers or stems that radiate out from the center of the plant
- Spreads mostly by above-ground stolons that can root at nodes
- Grows procumbently along the ground in dense clumps and mats
Smooth or Southern Crabgrass
The species Digitaria ischaemum has a smoother appearance than large crabgrass:
- Leaf blades and sheaths have very few if any hairs
- Blades are 1 to 6 inches long, approximately 1/4 to 1/2 inch wide
- Forms circular patches from finely branched flowering stems
- Spreads from underground root structures and aboveground stolons
- Has a lighter green color and is smaller than large crabgrass
Crabgrass Leaf and Seedhead Characteristics
Looking closely at crabgrass leaves and seedheads can also help identify it:
Leaves
- Leaves are rolled in the bud (an identifying feature of most grass species)
- Leaves have a membranous ligule where the blade and sheath meet
- Alternate leaves occur singly at intervals along the stem
- Leaves are often hairy on the surface and margins, giving a grayish cast
- Leaves have a coarse texture compared to lawn grasses
Seedheads
- Mature crabgrass plants produce finger-like vertical seedheads
- Seedheads emerge from a compressed sheath at the top of the stem
- Each stem branch produces up to 7 spikes, each 2–6 inches long
- Spikelets are arranged alternately along one side of the spike
- Large crabgrass seed is yellowish-brown while smooth crabgrass seed is purplish
Where Crabgrass Grows
Crabgrass thrives in open, sunny locations with plenty of bare ground:
- Readily invades thin, sparse lawns and areas damaged by foot traffic or pet urine
- Quickly colonizes newly disturbed soils in gardens, beds, or construction areas
- Flourishes in compacted, poor, dry soils that lack adequate fertility and irrigation
- Often sprouts in driveways, sidewalk cracks, gravel paths, or patio edges
It struggles to grow in dense, healthy turfgrass and deeply shaded areas. But once established, crabgrass is highly competitive with surrounding plants thanks to its rapid summer growth.
When Does Crabgrass Germinate?
Crabgrass seeds begin germinating when soils reach 55-60°F, which is normally sometime between late spring and early summer. The exact timing depends on your location:
- In southern zones, crabgrass may sprout as early as March or April
- In northern zones, it typically germinates in May or June
- Seeds may continue to germinate throughout summer whenever disturbance opens up space
Newly sprouted crabgrass starts out looking like grassy leaves emerging singly along stems. It can be mistaken for young grass seedlings at first.
Crabgrass Lookalikes: Differences From Lawn and Garden Grasses
Crabgrass shares some visual similarities with lawn and pasture grasses, especially before it begins flowering and seeding. Here are some differences that can help identify crabgrass:
Difference from Lawn Grasses Like Fescue and Bluegrass
- Crabgrass stems radiate and root out from a central point; lawn grasses do not spread this way
- Leaf blades are more coarse textured and wider (>1/4 inch) than lawn grasses
- Leaf sheaths and stems have hairs that give crabgrass a grayish tone
- Crabgrass leaves have visible membranous ligules
- Growth habit is patchy and spreading rather than forming a uniform lawn
Difference from Goosegrass
Goosegrass is sometimes mistaken for young crabgrass but has these distinct features:
- Much thinner leaf blades, similar to delicate hairs early on
- Forms a mat-like growth close to the ground rather than upright stems
- Stems root at nodes but are slender and wiry, not stout like crabgrass
- Ligule is a fringe of fine hairs rather than a membranous piece
Difference from Annual Bluegrass
Annual bluegrass is another common weedy grass but differs from crabgrass in:
- Leaf sheaths are rounded rather than flattened
- Leaves have boats-shaped leaf tips rather than tapering to a point
- Grows in winter and spring rather than summer
- Lacks hairs on leaves and stems; smooth texture
Difference from Quackgrass and Orchard Grass
These grasses have clasping auricles and no ligule, unlike crabgrass. Their leaf blades are continuous, not alternately attached. Growth habit is bunching rather than in spreading patches.
Controlling and Removing Crabgrass
Preventing crabgrass from establishing in the first place is important. Once established, removing crabgrass takes effort:
Cultural and Mechanical Control
- Maintain turfgrass density to crowd out weeds
- Fix compaction, irrigation issues, and nutrient deficiencies
- Spread pre-emergent herbicide in spring to stop seeds from sprouting
- Hand pull small patches; ensure root removal
- Hoe young plants before they produce seeds
- Overseeding with lawn grass can help crowd it out
Herbicide Control Options
- Post-emergent crabgrass killers like quinclorac, fenoxaprop, and MSMA can selectively control crabgrass after it sprouts
- Non-selective herbicides like glyphosate (Roundup) can spot treat but also kill lawn grass
- Pre-emergent herbicides like prodiamine and dithiopyr prevent crabgrass seeds from germinating
Careful identification is key before applying any herbicide to avoid damaging desired grass and plants. Always follow label directions carefully.
Frequently Asked Questions About Crabgrass Identification
What does crabgrass look like when it first starts to grow?
When crabgrass first sprouts, it looks similar to regular grass leaves. The leaves are light green and grass-like, emerging singly along short stems. It is low-growing at first. Once established, it takes on more of a mat-like habit.
What color is crabgrass?
Crabgrass can range from light green to grayish or even purplish. The hairy leaves often have a grayish cast. Established patches may take on a reddish-purple hue. Smooth crabgrass is greener than the large, hairy type.
How can I tell the difference between crabgrass and grass?
Check for crabgrass signs like coarse, wide leaf blades, hairy sheaths, spreading growth habit, and membership ligules. Lawn grass has narrower leaves, no hairs, grows in uniform bunches, and has different ligules. Crabgrass spreads via aboveground stolons while grass does not.
Does crabgrass have a flower? What does it look like?
Mature crabgrass produces finger-like seedheads branching off stems. The spikes are 2-6 inches long with globe-shaped spikelets arranged on one side. Large crabgrass has yellowish seeds while smooth crabgrass seeds are purplish.
What type of root system does crabgrass have?
Crabgrass has a fibrous shallow root system. But it also forms stolons that can root at nodes to spread the plant. Smooth crabgrass additionally has more extensive underground rhizomes. The root system is not as deep or extensive as lawn and garden grasses.
Conclusion
Being able to accurately identify crabgrass by its appearance and growth habits will ensure you can control this invasive annual weed. Look for leaf characteristics like rolled vernation, membranous ligules, coarse wide blades, and hairy sheaths and stems. Notice the mat-like spreading habit, stolons rooting at nodes, and purple-tinged color. Compare crabgrass to lawn grasses and other lookalikes to hone identification. Keeping crabgrass out of lawns and gardens requires early detection and rapid action while plants are still small and manageable.
Additional Detailed Information on Identifying Crabgrass
Crabgrass is one of summer’s most notorious weeds, overtaking lawns and gardens spaces with its rapid growth. Proper identification of this grassy invader is essential for successful control and prevention. Here is more in-depth information to help recognize crabgrass species by sight.
The Biology and Background of Crabgrass
Crabgrass, sometimes called large crabgrass or finger-grass, encompasses multiple summer annual grass species in the genus Digitaria including the common lawn invaders D. sanguinalis (hairy crabgrass) and D. ischaemum (smooth crabgrass).
Some key notes about crabgrass’ biology and life cycle:
- Originated in Europe/Mediterranean then spread to other temperate regions
- Thrives in warm 70-90°F summer temperatures
- Germinates in spring once soil temperatures reach 55-65°F
- Each plant can produce up to 150,000 seeds that persist in soil for years
- Dies after first frost in fall; leaves may turn reddish color
- Shallow fibrous root system with stolons that root at nodes
Understanding this life cycle helps explain crabgrass’ distinctive summer growth and reproduction. It goes dormant in cool weather and blooms prolifically once established in warm seasons.
Visual Differences Between Crabgrass Species and Varieties
While the most common home lawn crabgrasses are D. sanguinalis and D. ischaemum, there are subtle visual differences between crabgrass species and varieties that can aid identification:
Large/Hairy Crabgrass (Digitaria sanguinalis)
- Leaf blades up to 6” long covered in hairs, giving gray-green color
- Broad membranous ligule, hairy sheath throat
- Reddish-purple color near center of plant
- Aggressive stolon spread above ground
- Yellowish seedheads with spikes up to 6” long
Smooth Crabgrass (Digitaria ischaemum)
- Smoother leaf blades and sheaths with few hairs
- More upright habit, less stoloniferous spread
- Green to purple color, especially at base
- Slender branching stems turn whitish when dry
- Purplish seeds; spikes only 2” long
Blanket Crabgrass (Digitaria serotina)
- Peculiar spreading habit, not clumping
- Short broad leaves rarely longer than 2”
- Limited stolon spread, not aggressively invasive
- Excellent low-maintenance groundcover
Indian/Junglerice Crabgrass (Digitaria longiflora)
- Robust upright clumps up to 3’ tall
- Relatively large 1⁄2” wide leaf blades
- Panicles a distinctive pyramid shape, seeds midsummer
- Less weedy, more ornamental than other crabgrasses
There are also several varieties of large crabgrass, including fasciatus, ciliaris, and glabrescens, distinguished by minor leaf, ligule, and seed traits.
The Distinct Parts of Crabgrass Plants
Crabgrass anatomy shares features common to grasses. Breaking down key structures makes it easier to compare crabgrass visually to lawn grasses.
Stems (Culms)
- Coarse light green stems with swollen nodes
- Hairy leaf sheaths encircle each internode
- Digitate branching pattern with 5-7 branches at end of culm
- Stems radiate out from central root crown
Leaves
- Alternate leaf arrangement, 1 leaf per node
- Rolled vernation (coiled in bud) with parallel veins
- Hairy blades up to 6” long and over 1⁄4” wide
- Pointed leaf tips, tapering blade ends
- Membranous ligule at leaf collar; hairy sheath throat
Flowers and Seeds
- 5-7 spiky branches per seedhead, 2-6” long
- Spikelets arranged alternately along spikes
- Hairy spikelet bracts tipped with tiny sharp teeth
- Seeds loose at maturity, up to 300 per plant
Studying these details on an established crabgrass specimen shows the identifying features that differ from standard lawn and pasture grasses. New sprouts can then be accurately matched by characteristics.
Comparing Crabgrass Vegetatively to Other Grasses
It is easiest to identify crabgrass once it flowers and sets seed. But vegetatively, young crabgrass can resemble grass at first glance. A close look at leaves, stems, and growth habit is required for crabgrass vs. grass identification:
Crabgrass vs. Lawn Grasses
- Wider leaf blades with hairy sheaths (smooth lawns)
- Coarse texture and faster summer growth
- Stolons rooting at nodes (lawns bunch or spread by rhizomes)
- Poor sod formation, clumping patches
- Aggressive seedheads (lawns floral spikes are more delicate)
Crabgrass vs. Goosegrass
- Goosegrass leaves narrow like hairs; crabgrass blades wider
- Goosegrass mat-like; crabgrass has upright stems
- Goosegrass ligule a fringe of hairs; crabgrass broad membrane
- Weak goosegrass roots vs. crabgrass’ stolon rooting
Crabgrass vs. Foxtails
- Foxtail leaf blades flat, margins smooth; crabgrass margins rough
- Foxtail sheaths rounded; crabgrass sheaths flattened
- Foxtail seedheads like fox tails; crabgrass spikes branch
Crabgrass vs. Bahiagrass
- Bahia raised ligule, no hairs; crabgrass hairy ligule
- Bahia rolls leaves lengthwise; crabgrass rolls crosswise
- Bahia broader blades; crabgrass narrow and hairy
- Bahia extensive rhizome spread; crabgrass stolon spread
The visual differences become most apparent when comparing mature specimens side-by-side. But familiarity with crabgrass’ identifying features allows accurate identification at any growth stage.
Recognizing Crabgrass When It First Sprouts
Crabgrass seedlings can closely resemble young lawn grass at first, before taking on the spreading habit. What are signs it is crabgrass in the early growth stages?
- Single leaf blades – Emerge individually along stems, not in groups from buds
- Shallow germination – Sprout close to soil surface, lack deep root establishment
- No aura – Absence of silvery hairy aura on sheath and leaves
- Blade width – Grass seedlings have very narrow blades initially; crabgrass slightly wider
Also examine the sprout’s point of origin. Crabgrass tends to germinate in bare patches and thin turf rather than amid healthy grass. Its need for light explains this emergence pattern.
If crabgrass is suspected, uproot a few plants to check for stolons forming already at the base. Try rolling a leaf crosswise to see if it wraps diagonally around the stem. Grasses roll lengthwise.
Catching crabgrass early before it matures gives the best chance to halt its invasive spread. Quick identification and removal can protect your lawn or garden from takeover.
When and Where Crabgrass Germinates
Crabgrass sprouting follows a predictable timetable based on warming soil temperatures. Location offers clues too, as crabgrass infests open, bare areas first.
Seasonal Timing
- Early spring – Begins germinating once soils reach 55-65°F
- Mid to late spring – Peak germination period, especially after last frost
- Early summer – Secondary flush from continually ripening seeds
- Midsummer – Less germination once soil temps exceed 85°F
Timing varies by region, 2-4 weeks earlier in warmer southern zones. But crabgrass always takes advantage of spring’s warming trend whenever it occurs.
Location Cues
Crabgrass establishment favors these growing conditions:
- Full sun – does not thrive in dense shade
- Bare soil – invades gaps in turf or garden beds
- Compacted, poor, dry soils – avoids lush vigorous areas
- Near hardscapes – sprouts in cracks, edges, gravel
Spotting these high-risk areas before crabgrass appears allows pre-emptive treatment. Targeted early spring pre-emergent herbicide application works well on likely infestation sites.
While not failproof, noting location patterns provides clues for the observant gardener seeking to halt crabgrass before it conquers.
Special Techniques for Identifying Crabgrass
Beyond visual inspection, specialized tests can further verify if a suspect plant is indeed crabgrass:
Rooting at Nodes Test
Carefully dig up part of the stem and check for roots forming at the swollen nodes. Stoloniferous spread via nodal rooting is a trademark of crabgrass. Lawn grass stems will not have this characteristic.
Leaf Rolling Test
Try rolling a suspect leaf blade crosswise, perpendicular to the vertical stem. Crabgrass characteristically rolls diagonally in this direction. Lawn grass blades roll lengthwise.
Seedhead Examination
On a mature specimen, closely examine the flower and seed structure. Identifying characteristics like the one-sided spikes, globe-shaped spikelets, and seed color help confirm crabgrass.