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Invasive Plants in Pittsburgh

Identify them. Control their spread. Restore the land.

Invasive plants are nonnative species that can spread aggressively and interfere with local ecosystems. Across Pittsburgh, they can be found along roadsides, riverbanks, wooded slopes, vacant lots, parks, neighborhood properties, and community growing spaces.

Explore the plant guide Review safety guidance
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Protecting local growing spaces

Early identification can prevent a small patch from becoming a larger community problem.

Once established, invasive plants may crowd out native vegetation, reduce wildlife and pollinator habitat, weaken trees, interfere with food-growing areas, and make land restoration more difficult. Some species can also damage structures or create risks for people and animals.

Priority species

Six invasive plant concerns in Pittsburgh

Identification and mitigation methods vary by species. Confirm the plant before beginning any removal activity.

Japanese knotweed identification guide

01 · Invasive perennial

Japanese Knotweed

What to look for

  • Hollow stems that resemble bamboo
  • Distinct joints or nodes along the stems
  • Broad, pointed or heart-shaped leaves
  • Dense clusters of small white flowers in late summer
  • Thick stands that return from the same underground root system

It is frequently found near streams, roadsides, disturbed soil, vacant properties, rail corridors, drainage areas, and construction sites.

Why it is a problem

Japanese knotweed develops an extensive underground network of rhizomes. Small pieces of its roots or stems may produce new plants when moved.

  • Crowds out native plants and reduces plant diversity
  • Obstructs access to waterways and vacant land
  • Spreads into neighboring properties
  • Interferes with garden development and land restoration
  • Can leave exposed soil vulnerable to erosion after seasonal dieback

Mitigation

Do not casually mow, cut, dig, or transport knotweed. Cutting without containment can scatter viable pieces. Very small new patches may sometimes be carefully removed if all roots and rhizomes are contained. Established patches usually require repeated management over multiple growing seasons. Seek professional evaluation for large infestations and sites near water, buildings, utilities, gardens, or neighboring property.

Tree-of-heaven identification guide

02 · Invasive tree

Tree-of-Heaven

What to look for

  • Large compound leaves containing many leaflets
  • Smooth gray bark on younger trees
  • A strong unpleasant odor when leaves or twigs are crushed
  • Clusters of winged seeds on mature female trees
  • Numerous shoots emerging from roots or cut stumps

It is commonly seen in vacant lots, alleys, roadsides, industrial areas, woodland edges, and cracks near buildings or pavement.

Why it is a problem

Tree-of-heaven spreads through seeds and underground roots. Improper cutting may cause the root system to produce many new shoots.

  • Forms dense colonies and displaces native trees and shrubs
  • May damage pavement, walls, and disturbed structures
  • Spreads rapidly across neglected land
  • Serves as a preferred host for spotted lanternfly

Mitigation

Do not simply cut down a mature tree and assume it has been controlled. Small seedlings can sometimes be removed in moist soil if the entire root is extracted. Larger trees generally require a planned treatment sequence before removal. Trees near buildings, electrical lines, streets, or other hazards should be handled by qualified professionals.

Garlic mustard identification guide showing first-year rosette and second-year flowering plant

03 · Biennial woodland plant

Garlic Mustard

What to look for

First-year plants usually form:

  • Low clusters of rounded or kidney-shaped leaves
  • Scalloped leaf edges
  • Leaves that may smell like garlic when crushed

Second-year plants develop:

  • Upright flowering stalks
  • Triangular or heart-shaped leaves
  • Small white flowers with four petals
  • Long, narrow seedpods

Why it is a problem

Garlic mustard can form dense ground-level populations in shaded areas. It emerges early and competes with native woodland plants for sunlight, moisture, nutrients, and growing space. One unmanaged patch may produce many seeds and continue spreading for years.

Mitigation

Small infestations can be hand-pulled before seeds mature. Remove as much root as possible while minimizing soil disturbance. Flowering or seed-bearing plants should not be left on the ground, placed in ordinary compost, or transported loosely. Monitor the site in later growing seasons because seeds may remain in the soil.

Japanese stiltgrass identification guide

04 · Invasive annual grass

Japanese Stiltgrass

What to look for

  • Thin, pale-green leaves
  • A faint silvery stripe along the center of the leaf
  • Sprawling stems that may root where they touch soil
  • Dense patches along trails, gardens, woodland floors, and disturbed ground

It may resemble native grasses, so identification should be confirmed before removal.

Why it is a problem

Japanese stiltgrass spreads quickly across shaded or partly shaded ground and forms dense carpets that suppress native seedlings and other low-growing vegetation. Seeds may travel on footwear, lawn equipment, soil, animals, stormwater, vehicles, and tires.

Mitigation

Small patches may be hand-pulled before seed production. Larger areas may require carefully timed mowing or another site-specific method. Clean soil and plant material from tools, footwear, mower decks, tires, and equipment before leaving an infested area. Preventing seed production is central to long-term control.

Multiflora rose identification guide

05 · Invasive shrubs

Multiflora Rose and Invasive Bush Honeysuckles

What to look for

Multiflora rose commonly has long arching stems, compound leaves, clusters of small white flowers, red rose hips, and fringed structures where the leaf stalk joins the stem.

Invasive bush honeysuckles commonly have opposite leaves, arching woody stems, white, yellow, pink, or reddish flowers, red or orange berries, and hollow-centered mature twigs in several species.

Why they are a problem

  • Form dense thickets that restrict access
  • Crowd out native shrubs and wildflowers
  • Reduce native tree regeneration
  • Alter wildlife habitat
  • Spread into woodland edges, fields, vacant lots, and fence lines

Mitigation

Young plants may be pulled or dug in moist soil if most of the root system can be removed. Cutting larger plants without follow-up often results in vigorous regrowth. Repeated cutting may weaken some plants but can require sustained management. Remove fruiting material carefully and continue monitoring for seedlings.

Oriental bittersweet identification guide

06 · Invasive woody vine

Oriental Bittersweet and Other Invasive Vines

What to look for

  • Rounded leaves
  • Yellow seed capsules
  • Red or orange fruit
  • Fruit and flowers growing in clusters along the stems
  • Thick vines twisting around trees and shrubs

Other invasive vines of concern include Japanese honeysuckle, English ivy, porcelain berry, mile-a-minute vine, and wintercreeper.

Why they are a problem

Invasive vines can climb into tree canopies, block sunlight, increase branch weight, bend young trees, contribute to tree failure, and spread across fences, garden edges, woodland floors, and unmanaged lots.

Mitigation

Small vines may be pulled when soil is moist and roots can be removed safely. Do not pull heavy overhead growth from trees because falling vines and limbs can cause injury. Ground-level cutting separates a vine from its roots, but many species regrow unless the root system is also managed. Large vines and vines affecting mature trees should be evaluated by experienced workers.

Plants requiring extra caution

Do not include these plants in an ordinary community weed-pulling activity.

These species can cause serious injury or poisoning. Avoid casual handling and obtain reliable identification and professional guidance.

Giant hogweed identification and hazard guide

Severe contact hazard

Giant Hogweed

Giant hogweed sap can cause severe skin injury when exposed skin is subsequently exposed to sunlight. Sap entering the eyes can cause serious eye damage.

Do not touch, cut, mow, or attempt to remove suspected giant hogweed without expert guidance.

Poison hemlock identification and hazard guide

Highly toxic

Poison Hemlock

All parts are highly toxic if ingested. Common features include smooth hollow stems, purple blotches, finely divided fern-like leaves, and clusters of small white flowers.

Keep children and animals away. Do not burn the plant material.

Wild parsnip identification and hazard guide

Sap and sunlight hazard

Wild Parsnip

Wild parsnip sap may cause painful, light-sensitive skin burns. It often grows along roadsides and disturbed areas.

Avoid skin contact and obtain reliable identification before treatment.

Plan before acting

Before removing an invasive plant

1

Confirm the species

Many native plants resemble invasive species. Use several identifying characteristics, not only one leaf, flower, or photograph.

2

Evaluate the site

Check for food beds, play areas, waterways, storm drains, buildings, retaining walls, utilities, roads, neighboring property, and valuable native plants.

3

Determine its size

A few young plants may be managed differently from a mature colony with an extensive root system.

4

Choose the right method

Pulling, digging, cutting, mowing, covering, and herbicides do not work equally well for every plant. The wrong method may spread or stimulate it.

5

Plan for disposal

Do not begin removal until plant material and contaminated soil can be contained and disposed of safely.

6

Prepare for follow-up

Control is rarely completed in one day. Inspect treated areas repeatedly for regrowth and new seedlings.

Work safely

Safe handling, disposal, and herbicide use

A plant may continue spreading after it is cut. Seeds can mature on removed stems, and fragments of some species remain viable.

Handling and disposal

  • Wear suitable gloves, long sleeves, long pants, closed shoes, and eye protection when appropriate.
  • Contain flowering, fruiting, rooted, or seed-bearing material.
  • Do not place high-risk invasive plants in ordinary backyard compost.
  • Never dump plant material in vacant lots, wooded areas, alleys, waterways, or along roads.
  • Do not transport loose soil from an infested site.
  • Clean tools, shoes, tires, tarps, mower decks, and equipment before moving elsewhere.
  • Bag and solarize knotweed and other plants capable of surviving through fragments before disposal.
  • Follow current municipal waste requirements.
  • Never burn poison hemlock or unknown toxic plants.

Herbicide safety

Some established infestations cannot be controlled effectively by pulling or cutting alone. Herbicides may be part of an integrated plan, but they must be selected and applied carefully.

  • Read and follow the complete product label.
  • Confirm that the product is permitted for the site.
  • Protect food crops, native plants, people, pets, pollinators, soil, and water.
  • Follow timing, weather, protective-equipment, and application requirements.
  • Use a qualified or licensed applicator when required.
  • Seek professional guidance near streams, wetlands, drainage channels, community gardens, or public land.

This educational material does not replace the pesticide label, site-specific professional advice, municipal requirements, or applicable law.

Complete the work

Restore the area after removal

Removing invasive plants is only the first step. Bare or disturbed soil may be reinvaded if it is not stabilized and replanted.

Protect native plants

Preserve existing beneficial vegetation and reduce unnecessary soil disturbance.

Stabilize the site

Control erosion and apply appropriate mulch or other site-specific soil protection.

Replant thoughtfully

Use suitable native trees, shrubs, grasses, and flowering plants based on sunlight, moisture, soil, space, and community use.

Native vegetation can occupy open growing space, support pollinators and wildlife, stabilize soil, and improve the long-term resilience of the site. Continue monitoring and remove new seedlings before they become established.

A simple community response

See it. Identify it. Contain it. Manage it. Monitor it. Restore it.

See It

Notice unfamiliar plants spreading rapidly or forming dense patches.

Identify It

Confirm the species before taking action.

Contain It

Prevent seeds, roots, stems, and contaminated soil from moving.

Manage It

Use a safe, species-specific control plan.

Monitor It

Return throughout the growing season and in future years.

Restore It

Replant cleared areas with suitable native vegetation.

Protect Pittsburgh's growing spaces

Healthy gardens and neighborhood green spaces begin with informed stewardship.

By recognizing invasive plants, preventing their spread, and restoring treated land, residents can help protect community gardens, vacant lots, wooded areas, waterways, and neighborhood properties. Do not remove plants from public land or property you do not own without authorization. Seek professional assistance for large infestations, uncertain identification, hazardous plants, pesticide treatment, work near waterways, or plants affecting structures and utilities.

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