10 Plants You’re Not Allowed to Grow in the United States

Some plants might look beautiful or exotic, but in the United States, growing them can land you in legal trouble. Whether it’s because of their aggressive spread, harm to native ecosystems, or threats to human and animal health, several plants are banned at the federal or state level.

This guide will introduce you to 10 plants you’re not allowed to grow in the United States, with detailed reasons why they are restricted. From toxic weeds like Giant Hogweed to invasive aquatic threats like Hydrilla, knowing what not to plant is just as important as knowing what you can.

Whether you’re a home gardener, landscaper, or curious homeowner, this list will help you stay compliant with U.S. plant regulations while protecting your local environment. Let’s dive into which plants to avoid and why keeping them out of your garden is a smart (and legal) move.

1. Kudzu (Pueraria montana var. lobata)

Given its explosive and unrestrained spread, kudzu is sometimes known as “the vine that ate the South.” Originally brought from Asia in the late 1800s for erosion control and as a feed crop, it soon became invasive, particularly in the southeast U.S.

Under ideal conditions, kudzu can grow up to a foot every day and can overwhelm buildings, electricity lines, trees, and other structures. Its large root structure makes elimination once established somewhat challenging. Now regarded as a noxious plant in many states, including Georgia, Alabama, and Mississippi, it is aggressive and damages ecosystems by covering native flora and changing the balance.

Strict rules prohibiting the growing and distributing of kudzu have been published by the USDA and municipal governments. Should they be discovered on private land, removal might be mandatory, and offenders could pay hefty fines.

2. Giant Hogweed (Heracleum mantegazzianum)

Not just invasive but also dangerous for human health is giant hogweed. Originally from the Caucasus part of Eurasia, this tall plant was brought to North America as an ornamental species because of its amazing height and big white blossoms.

But it hides a poisonous secretion that, in sunlight, can inflict blistering, extreme burns, and long-term scars. Should it come into touch with the eyes, it can occasionally even cause either temporary or permanent blindness. Giant hogweed is listed as a federal noxious weed under the Plant Protection Act due to these hazardous properties.

Growing, selling, or moving this plant within the United States is unlawful. Authorities exhort individuals to notify environmental agencies of sightings. Professionals in hazmat suits are mandated in some areas for removal, which emphasizes even more the plant’s major threat to public health and natural biodiversity.

3. Hydrilla (Hydrilla verticillata)

Originating in Asia, submerged aquatic plants called hydrilla have seriously disrupted American rivers. Originally unintentionally brought through the aquarium trade, it is today regarded as one of the most troublesome invading aquatic plants in the nation.

Dense mats of hydrilla at the water’s surface block sunlight and choke off native aquatic vegetation. By changing oxygen levels, these mats affect fish and other aquatic life, disrupt leisure activities including boating and fishing, and impede water movement. It reproduces quickly using fragments, tubers, and turions, thereby making control efforts extremely difficult.

Lakes, rivers, and canals in numerous U.S. states—including Florida, Texas, and California—have yielded the plant. The USDA has declared hydrilla a nationally banned aquatic weed due to its aggressive character and influence on the surroundings. It is prohibited to cultivate or transport it; major resources are committed yearly to its management and elimination.

4. Cannabis (Certain Strains Depending on State)

In the United States, cannabis—also known as marijuana—occupies a convoluted legal posture. While some states expressly forbid its growing, others have approved its cultivation for either medical or recreational usage.

Under the Controlled Substances Act, cannabis is categorized as a Schedule I controlled substance on the federal level, so it is illegal to grow, possess, or distribute it independent of state legislation. These rules are enforced by the federal government, especially in relation to public land, major farming, or interstate trade.

In states where cannabis is allowed, people have to follow rigorous rules about security measures, plant count, and visibility. For personal use, adults in California, for instance, can have up to six plants per household but must make sure they are not easily reachable to young people. Breaking these guidelines could lead to heavy penalties or criminal accusations. Therefore, depending on your location, growing some strains of cannabis can be absolutely forbidden and result in legal actions.

5. Purple Loosestrife (Lythrum salicaria)

Originally from Europe and Asia, the perennial wetland plant purple loosestrife is Although its tall, vivid purple flower spikes made it formerly a popular attractive garden plant, today it is regarded as a major ecological danger across North America.

Thriving in marshes, this invading species spreads quickly by seeds and underground roots, outcompeting native plants. One mature plant might generate more than two million seeds annually. The dense monoculture produced thereby lowers biodiversity, disturbs natural water flow, and influences habitat quality for birds, fish, and other animals.

Many U.S. states have outlawed its sale, transportation, and cultivation due to environmental harm. Some local governments aggressively eradicate Purple Loosestrife from public areas; planting it on purpose could lead to fines. Ecological landscaping calls for native wildflowers among other alternatives. Some places have adopted certain beetles as a means of biological control to stop its spread.

6. Japanese Knotweed (Fallopia japonica)

Originally imported to the United States from East Asia as an ornamental and erosion-control plant, Japanese knotweed is a fast-growing, invading perennial plant. A nightmare for property owners and urban designers, it can grow through concrete, asphalt, and even building foundations and features bamboo-like stalks and heart-shaped leaves.

Mostly by underground rhizomes—which can lie dormant for years and regenerate from even small pieces—knuckweed spreads. This plant destroys infrastructure and outcompetes local plants, costing millions yearly in repairs and eradication.

Growing or transplanting Japanese knotweed is forbidden in places like New York and Oregon; many U.S. states categorize it as a noxious weed. Usually, its management calls for long-term monitoring and professional assistance. Local and state laws tightly control its cultivation in order to stop more spread and property damage caused by its destructive character and tenacity.

7. Tansy Ragwort (Jacobaea vulgaris)

A biennial or short-lived perennial plant, tansy ragwort seriously disturbs natural habitats and cattle. Originally from Europe and Asia, it was inadvertently brought to the United States and is currently most often found in the Pacific Northwest.

When ingested, it includes poisonous alkaloids that, in cattle, horses, and other grazing animals, can cause liver damage or death. Given that the plant stays poisonous even when dried in hay, it is very deadly. It travels readily from its seeds, which wind, animals, and vehicles distribute. Aggressively colonizing pastures, roadsides, and disturbed sites, Tansy Ragwort replaces natural vegetation.

These problems classify it as a noxious weed in some states, including Oregon and Washington. Mandatory removal orders may follow from growing or letting this plant spread. Many places control infestations by coordinated measures including mechanical removal, pesticides, and biological controls.

8. Salvinia molesta (Giant Salvinia)

Native to South America, giant salvinia is a floating aquatic fern that has become one of the most aggressive invading species in freshwater systems in the United States. It develops thick mats on the surface of the water and reproduces asexually, blocking sunlight and reducing oxygen levels, upsetting aquatic ecosystems.

Within a few days, these mats can double in scale and make irrigation, boating, and fishing impossible from water bodies. Its rapid expansion can potentially compromise infrastructure and choke water supplies. States including Texas, Louisiana, and Florida have seen invasions of lakes and rivers by giant salvinia.

It is on the federal noxious weed list because of its quick spread and environmental damage; its sale, transportation, or cultivation is absolutely forbidden in the United States. Authorities commit large funds to measures at containment and eradication, including biological control with Salvinia weevil. People who purposefully grow Giant Salvinia run significant legal risk.

9. Water Hyacinth (Eichhornia crassipes)

A free-floating aquatic plant with exquisite lavender blooms and quick reproduction is water hyacinth. Originally from the Amazon basin, it first made its way to the United States for decorative use in the 1880s. Still, it has lately turned out to be among the worst aquatic weeds on Earth.

By building thick mats that block sunlight and lower oxygen levels in the water, water hyacinth clogs rivers, causes navigation difficulty, and disturbs local aquatic life. These mats also offer mosquitoes somewhere to breed, therefore raising the possibility of vector-borne infections.

Water hyacinth has badly affected ecosystems in southern American states, including Florida and Louisiana. Several states classify it as a noxious weed; growing or transporting it is against the Federal Noxious Weed Act. The plant is strictly controlled despite its decorative value; officials advise the use of native aquatic plants instead. Penalties and deportation orders could be issued against violators.

10. Tree of Heaven (Ailanthus altissima)

Native to China, the fast-growing deciduous Tree of Heaven was brought to the United States in the 18th century. Originally utilized as a decorative and shade tree, it soon became clear to be an aggressive invader. Growing in a range of soil kinds, it generates compounds known as allelopathy that stop other plants from growing.

It can spread through both seeds and root suckers and compromise sidewalks, foundations, and sewage connections. With thousands of seeds produced annually, one tree can quickly colonize urban settings, roadsides, and damaged places. Furthermore, the main host for the invading spotted lanternfly, a major agricultural pest, is the Tree of Heaven.

Many states have issued cautions and prohibitions on planting or maintaining the tree due to its invasive character and contribution to pest outbreaks. Eliminating is challenging and usually involves either repetitive cutting or expert treatment with herbicides.

Bottom Line

Growing certain plants in the United States isn’t just discouraged—it’s illegal. Many of these banned species pose serious risks to native ecosystems, infrastructure, public health, and agriculture. Whether it’s Kudzu blanketing the South or Giant Salvinia choking freshwater systems, these plants are more than just garden nuisances.

Understanding which plants are restricted—and why—can help you make informed choices while staying on the right side of the law. When in doubt, always check local and federal regulations before planting unfamiliar species. By doing so, you’re contributing to a healthier, more balanced environment.

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