Catnip (Nepeta cataria)

Synonyms: Cataria vulgaris, Glechoma cataria, Nepeta vulgaris, Nepeta americana, Nepeta citriodora, Calamintha albiflora

Common Names: Catmint, catswort, catwort

Description:

Catnip (Nepeta cataria) is a mint-family plant from Europe and Asia that was brought to North America as a garden herb and has since escaped into the wild [1][4]. It is best known for an oil in its leaves that excites most cats [3]. MISIN tracks it because it self-seeds freely and can spread into pastures, roadsides, and other disturbed ground, where it forms weedy patches [6].

Habit:

Catnip is a bushy, upright plant that usually grows 1 to 3 feet tall [3][6]. Its stems are square in cross-section and covered in fine white hairs, a common trait of the mint family [6]. The gray-green leaves are heart-shaped to triangular with coarse, saw-like teeth along the edges, and the underside looks whitish because it is so densely hairy [6]. Small two-lipped flowers, white with tiny purple spots, crowd into dense clusters near the tops of the stems [6]. Crush a leaf and it gives off a strong minty smell ? the same scent that draws cats [3].

Catnip is easiest to spot in summer, roughly June through fall, when the flower clusters stand out on tall stems [6]. Earlier in the year it appears as a low, gray-green leafy clump, so check disturbed ground and fence lines from late spring onward [3][6].

At-a-glance cues:

1. Square stems covered in fine white hairs [6]
2. Gray-green, heart-shaped leaves with saw-toothed edges and a whitish, hairy underside [6]
3. Dense clusters of small white flowers dotted with purple near the stem tips [6]
4. Crushed leaves smell strongly of mint and attract cats [3]

Leaves:

1. Arrangement: opposite ? two leaves per node along the stem [2][6]
2. Shape: triangular to heart-shaped, with a rounded or notched base [2][6]
3. Margin: coarsely toothed, like the edge of a saw blade [6]
4. Surface: gray-green and downy; the underside is densely hairy and looks whitish [6]
5. Size: up to about 3 inches (roughly 8 cm) long [5]

Stems:

1. Habit: herbaceous (non-woody), upright, branching, 1 to 3 feet tall [3][6]
2. Cross-section: square ? a hallmark of the mint family [6]
3. Surface: covered in short, fine white hairs [6]
4. Color: light green [3]

Flowers:

1. Color: white with small pale-purple spots [6]
2. Shape: small and two-lipped (bilabiate), about 1/4 inch long [2][6]
3. Arrangement: in dense, crowded whorls forming spike-like clusters near the tops of the stems [6]
4. Bloom time: late spring through fall, roughly May to October [5][6]

Fruit and seeds:

1. Fruit type: a dry cluster of four small nutlets held in the dried flower base, splitting apart when ripe [2][6]
2. Seed: smooth, oval, reddish-brown, about 1/16 inch long, often with two pale spots at one end [2][6]
3. Count: four nutlets (seeds) per flower [6]
4. Dispersal: seeds drop near the parent plant and are also moved in soil, on equipment, and along roadsides [6]

Habitat:

Catnip is native to a wide band stretching from southern Europe across Asia to Japan, plus northwestern Morocco [4]. It was carried to North America as a garden and medicinal herb, escaped cultivation, and is now naturalized across much of the United States and Canada [1][6].

It favors open, sunny, disturbed ground and dry soil. Look for it in pastures, fence rows, barnyards, vacant lots, stream banks, roadsides, railroad edges, and waste places such as dumps and parking-lot margins ? often near old homesteads and abandoned fields [6]. It tolerates many soil types but does not thrive in deep shade or wet ground.

Reproduction:

Catnip is a short-lived perennial ? it dies back to the ground each winter and regrows from the same roots the next spring [3]. It spreads two ways. Most new plants come from seed: a single plant produces large numbers of seeds that fall close by and are easily carried farther in soil, on shoes and clothing, on mowers and other equipment, and along roadsides [6]. It also creeps outward a short distance using short rhizomes (horizontal underground stems), so a patch can slowly widen on its own or push in from a neighbor's yard [3][6].

Plants flower from late spring through fall and set seed soon after [5][6]. For control timing, the key is to remove plants before the flowers turn to seed ? cutting, pulling, or mowing in late spring to early summer stops a patch from reseeding itself [6].

Impact and Damage:

For most homeowners, catnip is a nuisance rather than a hazard. It is not a serious threat to people, but it self-seeds so freely that it can become weedy and crowd out other plants in gardens, flower beds, and lawns [3][5]. Cats are strongly drawn to it and may flatten or dig up a patch, and eating large amounts can upset a cat's stomach, causing vomiting or loose stools [5].

For natural area stewards, catnip's documented impact is limited compared with aggressive invaders. It is mainly a plant of disturbed, sunny ground ? pastures, field edges, roadsides, and waste places ? and is not generally considered a strong invader of healthy, intact natural areas [3][6]. Where the ground is already disturbed, it can form dense self-seeded stands that occupy space other plants would fill [6]. Tracking where it shows up still helps managers watch for spread into new openings.

Similar species:

A few mint-family plants are mistaken for catnip. The surest checks are catnip's gray-green, downy, saw-toothed heart-shaped leaves, its white flowers dotted with purple in clusters at the stem tips, and its strong minty "catnip" smell when crushed [2][6].

Garden catmint (Nepeta ? faassenii and related ornamental catmints) shares the catnip name and is the closest match. It is grown in flower beds for its showy spikes of blue to purple flowers and tidy, mounded shape, while wild catnip is taller, looser, and weedier with plain white flowers [3][5]. Most garden catmints are sterile hybrids that do not self-seed, so they rarely escape the way catnip does [5].

White horehound (Marrubium vulgare) is another gray, downy mint of dry pastures and waste ground that can look similar from a distance. Up close its leaves are rounded and deeply wrinkled rather than heart-shaped and saw-toothed, and its small white flowers sit in tight balls tucked where the leaves meet the stem instead of in clusters at the stem tips [4].

Motherwort (Leonurus cardiaca) is a square-stemmed weedy mint that grows in the same kind of disturbed ground. It is easy to separate by its deeply lobed, hand-shaped upper leaves and its small pink flowers clustered in the leaf joints along the stem, rather than catnip's toothed heart-shaped leaves and white-flowered tips [4].

Monitoring and rapid response:

Signs to watch for:

1. Bushy, gray-green plants 1 to 3 feet tall on disturbed, sunny ground ? fence lines, pastures, roadsides, vacant lots [6]
2. Square, hairy stems and heart-shaped, saw-toothed leaves with a whitish underside [6]
3. Clusters of small white, purple-dotted flowers near the stem tips in summer, and a strong minty smell when a leaf is crushed [3][6]

What you can do:

1. Hand-pull or dig out small patches, taking the shallow roots and short underground stems ? easiest after rain when the soil is loose [6]
2. Do it before the flowers set seed (late spring to early summer) to stop the patch from reseeding [6]
3. Cut or mow flowering stems and bag the seed heads so seed does not scatter; repeat through the season, since plants regrow and rebloom [5][6]
4. Smother a cleared patch with thick mulch or cardboard to block regrowth from seed in the soil [6]
5. For natural areas, volunteer crews can knock back larger stands with repeated mowing and pulling across a site, and should treat small outlying patches first to keep them from spreading into new openings [6]

When to call a professional:

1. Large pasture or right-of-way infestations that keep returning despite mowing and pulling [6]
2. Patches that regrow strongly from underground stems after repeated hand removal [6]
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. USDA NRCS Plants Database. Nepeta cataria L. plants.usda.gov
2. Native Plant Trust, Go Botany. Nepeta cataria (catnip). gobotany.nativeplanttrust.org
3. University of Wisconsin?Madison Division of Extension. "Catnip, Nepeta cataria." Wisconsin Horticulture. hort.extension.wisc.edu
4. Plants of the World Online (POWO), Royal Botanic Gardens, Kew. Nepeta cataria L. powo.science.kew.org
5. NC State Extension Gardener Plant Toolbox. Nepeta cataria (Catmint, Catnip, Catswort). plants.ces.ncsu.edu
6. Ohio State University Weed Guide. "Catnip (Nepeta cataria)." weedguide.cfaes.osu.edu

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