How to identify weeds in your lawn

Field tests for each look-alike pair

Dandelion vs cat's ear. Both make yellow flower heads, milky sap and wind-blown seed. Pick a flower stalk. The NC State Plant Toolbox describes dandelion stalks as hollow, leafless and unbranched, with leaves deeply toothed and pointing backward. Cat's ear has densely hairy leaves and flower stalks that are typically branched. Hairy leaf plus branched stalk means cat's ear. Virginia Cooperative Extension adds a third look-alike: sow thistle carries several flowers per upright stem.

Broadleaf plantain vs buckthorn plantain. Both are rosettes. Broadleaf plantain has much wider leaves and flowers along the upper half of its stalk; buckthorn (narrowleaf) plantain has narrow leaves and a fuzzy white flower head at the top of the spike (Virginia Cooperative Extension).

White clover vs wood sorrel vs black medic. All three show three leaflets. Flowers settle it fastest: white clover has white globe-shaped clusters, wood sorrel single yellow flowers, black medic yellow globe-shaped clusters. Without flowers, look at the leaflets. Wood sorrel's three leaflets are folded. The RHS clover guide notes white clover's rounded leaflet tips, often with a white mark, and a tiny point at the tip of each black medic leaflet, which are followed by black seed pods.

Creeping charlie vs wild violet. Both like shade and both resist easy removal. Virginia Cooperative Extension says growth habit and leaf shape separate them: ground ivy has rounded, scalloped leaves and runners that root at the nodes; wild violets grow in clumps from rhizomes and have heart-shaped leaves. Crush a leaf as well: the NC State ground ivy page describes an aromatic mint-family plant with square stems. The full profile is on the creeping charlie page.

Creeping buttercup vs creeping charlie. Both creep and root along runners. The leaf is the test: creeping buttercup leaves are divided into three deeply lobed, toothed leaflets covered in small hairs, while ground ivy leaves are single and rounded. The flowers differ too: glossy five-petaled yellow against small purple tubes. The RHS notes that buttercups are harmful if eaten and can irritate skin, so wear gloves when you dig them out.

Speedwell vs chickweed. Both are small and sprawling in cool weather. Corn speedwell has bright blue flowers, rounded toothed lower leaves and soft white hairs over the whole plant. Common chickweed has light green leaves with little or no hair; its relative mouse-ear chickweed has small, cupped, hairy leaves that turn darker green (Virginia Cooperative Extension).

Henbit vs purple deadnettle. Both are square-stemmed winter annuals that flower in spring. Deadnettle's upper leaves have short stalks and often a reddish-purple tint; henbit's upper leaves have no stalks.

Crabgrass vs goosegrass. Crabgrass sprawls and its stems root at the nodes; goosegrass sends stems out like the spokes of a wheel and doesn't root. Crabgrass centers turn purplish, goosegrass centers whitish (Virginia Cooperative Extension). Penn State Extension's crabgrass page adds the hairs: large crabgrass has long sparse hairs on both leaf surfaces and the sheaths, smooth crabgrass only a few at the base of the blade.

Nutsedge vs grass. Roll the stem between finger and thumb. A triangular stem means a sedge. Yellow nutsedge has yellowish flowers and stems as long as or shorter than the basal leaves; purple nutsedge has purplish flowers and stems longer than the leaves.

What the weeds say about your lawn

Weeds move in where grass is struggling, so a patch of one species is a clue to the site. The links below come from Virginia Cooperative Extension unless stated; treat them as reasons to test the soil, not as a diagnosis.

• Wet or poorly drained soil: nutsedge (also overwatered lawns), common and mouse-ear chickweed, ground ivy, buttercups, wild onion and wild garlic. The RHS says wet or waterlogged lawns favor creeping buttercup, and that waterlogging is common when heavy soil is compacted.
• Compaction, low pH and short mowing: annual bluegrass likes low pH, compaction, poor drainage, shade and lawns cut short. Moss points to low pH, wet or compacted soil, shade and low fertility.
• Low fertility: clover and wood sorrel, and plantains. Clovers fix their own nitrogen, which is why they stay green where grass is pale; the RHS adds that they cope with poor, dry soils. Speedwell turns up in dry areas with low fertility.
• High fertility: henbit and deadnettle, and buttercups.
• Shade: wild violet, ground ivy, chickweed and annual bluegrass.
• Mowing too short and thin turf: crabgrass and goosegrass do well in close-cut turf. Penn State notes crabgrass is most common in sunny sites with thinning turf and tolerates mowing at half an inch or less.

Cultural control: what extension services recommend first

The sources agree that a dense lawn is the main defence, because most weeds need light and bare soil to start.

1. Test the soil and adjust pH and fertilizer to the result, rather than guessing (Virginia Cooperative Extension). Purdue's 7 Simple Steps to a Better Home Lawn puts most fertilizing in the fall for cool-season grass; your local extension office has the timing for warm-season lawns.
2. Mow high and often. Purdue sets cool-season lawns at 3 inches or more and never removes more than a third of the blade at once. Penn State says about 3 inches with regular mowing deprives young crabgrass of light; Virginia Cooperative Extension suggests 3.5 to 4 inches against crabgrass and goosegrass.
3. Fix drainage and compaction by aerating and top-dressing with compost, which works against chickweed, buttercups and ground ivy.
4. Overseed thin areas so that new grass, not weeds, fills the gaps.
5. Let in light where trees and shrubs shade the turf; ground ivy, violets and chickweed lose their edge in brighter spots.
6. Hand-pull at the right moment. Chickweed before it flowers, young plantains, nutsedge while it has fewer than five leaves (older plants can resprout from their nutlets), dandelions while small and after rain when the soil is loose. Get the whole plant: ground ivy and creeping buttercup root along their stems, so lift those sections too. The RHS suggests raking creeping buttercup before mowing so the mower catches the runners.

Some of these "weeds" are worth keeping. The RHS describes clovers as drought-tolerant wildflowers valuable to bees, and creeping buttercup as a good plant for pollinators in a flower-rich lawn. If you'd rather have a wildflower lawn, the wildflower identification guide covers what you might be encouraging.

If you decide to use a herbicide, follow the label and local rules. Identification matters here: Virginia Cooperative Extension notes that ground ivy and violets resist many broadleaf products and that not every product that controls yellow nutsedge works on purple nutsedge, so check that the label names your weed.

When a photo helps

Most lawn weeds are easy once flowering and hard as mown leaves. A sharp photo of the whole plant, with a flower or seed head if there is one, is the best starting point. Plant Identifier names the plant from one photo and gives its scientific name, which you can then check against the chart above. The app shows no confidence score and no list of alternative species, so run the matching field test yourself: hollow stalk, triangular stem, leaflet tip. If the answer surprises you, the follow-up chat under the result in Plant Identifier lets you ask how that weed differs from the one you suspected. For pets that graze the lawn, see plants that are poisonous to dogs, and call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 if your dog has eaten something you can't name.