Botanical Name: Cytisus scoparius

Common Name(s): Scotch broom, common broom

Habitat: Open, disturbed sites, roadsides, pastures, and clearcuts. It thrives in full sun and well-drained soils.

Type of Invasiveness: This aggressive shrub forms dense, impassable thickets that crowd out native plants and forage species. It is highly flammable, creating significant fire hazards, and its seeds can remain viable in the soil for decades. Best Control Method: For young plants (pencil thickness or less), hand-pulling when the soil is moist is highly effective. For mature shrubs, use a specialized weed wrench to extract the taproot, or cut the trunk below the soil line during the dry summer months to prevent resprouting.

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Botanical Name: Genista monspessulana

Common Name(s): French broom, Montpellier broom

Habitat: Coastal scrub, oak woodlands, disturbed areas, and road verges.

Type of Invasiveness: Similar to Scotch broom, it aggressively colonizes disturbed areas,

displacing native flora and creating extreme fire risks due to its dense, volatile foliage. It

produces copious amounts of seed.

Best Control Method: Hand-pulling or wrenching is effective for smaller infestations

before they set seed. Repeated mowing or cutting can eventually exhaust the root system,

but controlled, targeted herbicide application on cut stumps is often necessary for large

stands.

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English ivy

Botanical Name: Hedera helix

Common Name(s): English ivy, common ivy

Habitat: Forest understories, riparian zones, urban parks, and residential areas.

Type of Invasiveness: A relentless free-climber and groundcover. On the ground, it creates

"ivy deserts" where nothing else can grow. When climbing, it can easily strangle mature

trees, block sunlight to the canopy, and add enough weight to cause trees to collapse in

storms.

Best Control Method: For climbing vines, create a "survival ring" by cutting the vines at

shoulder height and the base of the trunk, leaving the upper vines to die and decay in the

tree. For groundcover, pull the vines by hand, ensuring you remove the root systems, and

dispose of them in the trash.

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Himalayan blackberry

Botanical Name: Rubus armeniacus

Common Name(s): Himalayan blackberry, Armenian blackberry

Habitat: Riparian areas, forest edges, clearcuts, roadsides, and unmaintained urban lots.

Type of Invasiveness: Forms towering, impenetrable thickets of stout, deeply-ridged

thorny canes. It aggressively overtakes native vegetation, limits the movement of large

wildlife, and spreads rapidly via seeds distributed by birds.

Best Control Method: Mechanical removal using a brush mower or loppers to clear the

canes, followed by manually digging out the massive root crowns with a shovel. For very

large areas, applying a targeted systemic herbicide to freshly cut stumps is highly effective.

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Evergreen blackberry

Botanical Name: Rubus laciniatus

Common Name(s): Evergreen blackberry, cut-leaf blackberry

Habitat: Forest edges, riparian corridors, and disturbed sites, often mixed with Himalayan

blackberry.

Type of Invasiveness: Originally introduced for fruit production and landscaping, this

heavily armored, thorny vine forms dense thickets similar to the Himalayan variety. It easily

escapes cultivation and outcompetes native shrubs and young trees.

Best Control Method: Control is identical to Himalayan blackberry: cut down the above-

ground canes and manually dig out the entire root crown, or apply targeted herbicide to the

cut stems to prevent vigorous resprouting.

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Reed canary grass

Botanical Name: Phalaris arundinacea

Common Name(s): Reed canary grass

Habitat: Wetlands, stream banks, wet meadows, and ditches.

Type of Invasiveness: This tall, coarse perennial grass forms massive, dense single-species

stands that choke out native wetland plants. It alters the hydrology of streams by trapping

silt and narrowing waterways, degrading habitat for salmon and amphibians.

Best Control Method: Eradication is extremely difficult due to dense rhizomes. Small

patches can be carefully dug out or smothered with heavy landscape fabric for multiple

years. Large patches typically require repeated mowing followed by aquatic-approved

herbicide treatments in late summer.

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Japanese knotweed

Botanical Name: Fallopia japonica (syn. Polygonum cuspidatum)

Common Name(s): Japanese knotweed, fleeceflower

Habitat: Riverbanks, roadsides, disturbed areas, and urban lots.

Type of Invasiveness: One of the most destructive invasive plants worldwide. It has a

massive, deep rhizome system that can punch through asphalt, concrete foundations, and

retaining walls. Even a tiny fragment of root or stem can sprout a new plant, meaning it

spreads rapidly during floods or improper soil moving.

Best Control Method: **Do not mow or dig it.** Cutting or digging stimulates the root

system to spread further, and fragments easily create new infestations. The only reliable

control method is targeted foliar herbicide application or direct stem injection by a licensed

professional in late summer.

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Giant knotweed

Botanical Name: Fallopia sachalinensis

Common Name(s): Giant knotweed, Sakhalin knotweed

Habitat: Similar to Japanese knotweed; primarily riverbanks, riparian zones, and disturbed

moist soils.

Type of Invasiveness: Similar to Japanese knotweed but even larger, reaching up to 15 feet

tall with leaves that can be over a foot long. It aggressively dominates riparian areas,

increasing erosion risks in the winter when the massive canes die back, leaving bare soil.

Best Control Method: Follows the exact same strict protocol as Japanese knotweed: do not

cut, dig, or mow. Professional, timed herbicide application is required to exhaust the deep

rhizomes.

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Garlic mustard

Botanical Name: Alliaria petiolata

Common Name(s): Garlic mustard, Jack-by-the-hedge

Habitat: Forest understories, trail edges, and shaded yards.

Type of Invasiveness: This biennial weed forms dense carpets that smother native spring

ephemeral wildflowers. Worse, it produces allelopathic chemicals in its roots that actively

suppress the growth of surrounding plants and beneficial soil fungi that native trees rely on.

Best Control Method: Hand-pulling is very effective, but you must ensure you pull the

entire taproot (a gentle twisting motion helps). It must be pulled before it goes to seed, and

all pulled plants must be securely bagged and put in the trash, as they can continue to

mature seeds even after being uprooted.

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Giant hogweed

Botanical Name: Heracleum mantegazzianum

Common Name(s): Giant hogweed, cartwheel-flower

Habitat: Riparian areas, ravines, roadsides, and vacant lots.

Type of Invasiveness: Beyond its ecological threat of crowding out native vegetation, Giant

Hogweed is a **severe human health hazard**. The plant's clear, watery sap contains

photosensitizing chemicals. If the sap touches your skin and is exposed to sunlight, it causes

severe, blistering third-degree burns and permanent scarring.

Best Control Method: **Do not touch this plant without full protective gear** (gloves, long

sleeves, eye protection). Small plants can be carefully dug up. For larger plants, cut the

taproot several inches below the soil line. Report sightings to your local invasive species

council immediately.

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Purple loosestrife

Botanical Name: Lythrum salicaria

Common Name(s): Purple loosestrife

Habitat: Wetlands, marshes, stream banks, and lake shores.

Type of Invasiveness: A single mature plant can produce over two million seeds annually.

It aggressively invades wetlands, completely replacing diverse native habitats with dense,

uniform stands that provide no food or nesting material for native waterfowl and

amphibians.

Best Control Method: Small, isolated plants can be carefully dug out before they flower.

However, any root fragments left behind will resprout. For established populations, the

most successful long-term control is biocontrol (using host-specific beetles introduced by

wildlife agencies) combined with targeted aquatic herbicide.

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Giant reed

Botanical Name: Arundo donax

Common Name(s): Giant reed, wild cane

Habitat: Riparian corridors, floodplains, and ditches.

Type of Invasiveness: Resembling bamboo or corn, this massive grass can grow over 20

feet tall. It consumes enormous amounts of water, alters stream flows, displaces native

willows and cottonwoods, and poses a severe fire risk because the huge stands burn

incredibly hot, even when green.

Best Control Method: Physical removal is incredibly difficult due to massive, woody

rhizomes. Cutting the canes down and immediately painting the fresh stumps with a

concentrated, aquatic-safe systemic herbicide is generally the most effective method,

though it often requires years of follow-up.

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Tree of heaven (Ailanthus altissima)

English ivy (Hedera helix)

Scotch broom (Cytisus scoparius)

French broom (Genista monspessulana)

Himalayan blackberry (Rubus armeniacus)

(Cut-leaf / evergreen type) blackberry Rubus spp. used in landscaping

Reed canary grass (Phalaris arundinacea)

Japanese knotweed (Fallopia japonica)

Giant knotweed / related knotweeds (Fallopia sachalinensis and close relatives)

Garlic mustard (Alliaria petiolata)

Giant hogweed (Heracleum mantegazzianum)

Purple loosestrife (Lythrum salicaria)

Giant reed (Arundo donax)

Bluebells (commonly Spanish bluebell, Hyacinthoides hispanica) — can naturalize and spread in some areas

If by “blue bells” you meant English bluebell (Hyacinthoides non-scripta) instead of Spanish bluebell, tell me and I’ll swap the entry.