Invasive plants ruin the beauty of your yard, make extra work, and cost money to get rid of. Some–like dandelions–appear as volunteers. Others–like buckthorn–are planted by homeowners because of their looks and can take over the yard. A few–like English ivy–are toxic to humans and pets.
Here are some of the worst offenders–and how to get rid of them.
Dandelions
Dandelions are not considered invasive in the US because some species are native. Others come from Europe and Asia. It is designated as a weed.
- Long taproot makes total removal difficult. Taproot can grow to three feet long.
- Any part of the root remaining in the ground will resprout.
- Fluffy seed heads are easily spread by the wind or on animal fur.
- One single plant can produce up to 20,000 viable seeds.
Dig out the plants when they first appear. It is easier to remove the entire root when the plant is young and the earth is moist. If you are not sure you got all of the roots, spray a little pre-emergent dandelion-specific herbicide into the hole to prevent re-growth.
Spray broadleaf herbicides containing 2,4-D, dicamba, or MCPP on individual plants and larger infestations. They do not harm grass but can kill flowers and other leafed plants. Swabbing 2,4-D on one or two individual dandelion leaves per plant is enough to kill it. This method protects surrounding broad-leafed growth.
Herbicides do not kill dandelion seeds. Any that blow into your yard will likely sprout and have to be treated as they appear.
Quackgrass
Quackgrass is often referred to as couch grass, Medusa’s Head, and twitch grass among other names. It is native to Europe, North Africa, and Asia. It is difficult to control and almost impossible to eliminate.
- On the USDA’s restricted noxious weed seed list.
- Common in all of North America.
- Long rhizomes that spread the weed.
- Cut root pieces regrow.
- Also reproduces through seed production.
Quackgrass is difficult to completely remove by digging. Established plants have rhizomes up to two feet long. Any piece not removed can regrow. Continuous and persistent digging controls the weed but usually fails to eliminate it. Tilling is a double-edged sword. It pulls up rhizomes that can be raked off but always leaves bits and pieces that re-sprout.
Pre-emergent herbicides are not effective because quackgrass grows through them. No herbicide specifically controls it. Glyphosate is non-selective. It kills quackgrass–sometimes after repeated applications–but also kills surrounding plants if over-sprayed.
The best defense against quackgrass is a thick healthy lawn that chokes out the weed and prevents germination.
Canada Thistle
Canada thistle–also known as field thistle, corn thistle, and creeping thistle–is native to Europe and arrived in North America in the 1600s.
- Listed as an invasive noxious weed in 43 states.
- Has invaded over 20 national parks suppressing native plants.
- If left unchecked, it takes over fields, gardens, and yards.
- One of the most invasive weeds.
- Extensive root system that regrows.
- Multiple seed pods per plant. Mature fluffy seed heads are carried long distances by the wind.
Digging out Canada thistle is only effective if you remove the entire root system. Any small part of the root will regrow the following year. Cultivation increases root pieces. Mowing spreads seeds. Glyphosate is not very effective.
Spray the plants with 2,4-D or use a brush to coat a few leaves with the herbicide. (Brushing prevents overspray from killing surrounding plants.) The plant dies along with most of the root system. Inspect the area regularly and treat any regrowth early in the year. Be consistent and you can eventually eliminate the infestation.
Wild Violets
The beautiful little purple flowers of wild violet are very attractive–until they take over your yard and flower beds. Controlling them or killing them usually takes years of effort. Wild violets are native to North America.
- Reproduce using seeds, rhizomes, and root bulbs.
- Seeds attract ants which carry them to new locations.
- Leaves and flowers are edible and used medicinally, but the roots, fruit, and seeds are poisonous.
- Leaves are waxy in spring and summer and do not absorb herbicides easily.
- Extensive rhizome formations reduce herbicide effectiveness.
You may never get rid of wild violets but there are ways to control them. Cut them to ground level in the spring, and cover the area with cardboard, and mulch. Spot spraying with glyphosate slows them down but won’t kill them off–like it does with other plants. Repeated applications are necessary.
Wild violets can be dug out but will reappear the following year if the roots and rhizomes are not completely removed. Thick healthy lawns prevent wild violets from taking root.
Wild Parsnip
Wild parsnip–also known as poison parsnip–is invasive and dangerous. It is native to Europe and Asia and was brought to North America for its edible roots. It has since spread throughout the continent.
- Considered invasive and a noxious weed in several states.
- Causes serious rashes and blistering of human skin and increases sensitivity to sunlight.
- The sap is toxic–especially to pets that might chew or lick the plant.
- Remains viable in soil for up to 4 years.
Small infestations can be dug out. The entire taproot must be removed or it will regrow. Inspect and continue to dig them out every few weeks. Glyphosate or 2,4-D Amine (specific for wild parsnip) sprayed on the leaves kills the plant. Spray before it blooms and forms seeds. Wild parsnip plants reappear every year until all remaining seeds have sprouted.
Do not burn or compost wild parsnip. Let it dry in sealed plastic bags for at least a week, then dispose of them in a landfill.
Mowing gets rid of wild parsnip. Cut it early in the year and clean your lawnmower to prevent spreading seeds. It has to be cut yearly until no seeds remain. Herbicide sprays kill growing plants but do not eliminate seeds. The wild parsnip needs to be sprayed every year until seeds stop sprouting.
Buckthorn
Buckthorn easily outcompetes native plants for light, nutrients, and moisture. Originally used as a hedge, it spreads quickly and is an invasive plant. Many jurisdictions are making concerted efforts to eradicate buckthorn.
- Listed as invasive in many northern and central states.
- Self-seeding. Seeds are also spread by birds after eating the fruit.
- No insects attack it.
- No known plant diseases infect it.
- Spreads quickly and threatens wildlife habitat.
- Serves as a host to crown rust fungus and soybean aphids.
It usually requires several years to completely remove buckthorn from your yard. Small plants–up to 1” in diameter–can be pulled out by hand. Cut anything bigger close to the ground and apply glyphosate or triclopyr herbicide within 30 minutes. Herbicide can also be sprayed on the leaves of smaller plants. It is drawn down into the roots to kill the plant.
A herd of goats can eliminate buckthorn in short order. Not everyone has goats or property to contain them.
Seeds remain viable for up to five years. Whichever method you use, be prepared to deal with buckthorn regrowth for years.
Chinese Wisteria
Chinese Wisteria arrived in the US in 1816 and was used as an ornamental plant. It lives for over 50 years.
- Considered invasive in at least 19 states and some national parks.
- Causes building damage by growing into cracks and holes.
- Wraps tightly around tree trunks and branches–eventually girdling and killing the host.
- Kills native vegetation by denying sunlight and smothering.
The most effective option is a combination of cutting and chemical application. Cut the vine close to the root and apply triclopyr or glyphosate to the trunk. The herbicide is carried into the root system and kills the entire plant in about a week. You can then dig out the roots without fear of any regrowth. Herbicides can be sprayed on the leaves to kill the roots but it usually requires several applications to completely eradicate the plants.
Smaller plants and infestations can be pulled out by hand. You can also dig them out. Both methods require repeated cutting and/or digging because bits of remaining root resprout. Bag and dispose of the cut plants.
English Ivy
English ivy is a beautiful plant used as ground cover and as a climbing vine. It is native to Europe and arrived in North America with early immigrants.
- Becomes invasive.
- Difficult to control.
- Chokes native vegetation and kills trees it infests. Carries bacterial leaf scorch that destroys some tree species.
- Considered invasive in many eastern states and a noxious invasive weed in the Pacific Northwest.
- Leaves and berries contain glycoside hederin–a toxic substance that causes diarrhea, fever, muscle weakness, and coma among other symptoms.
If it grows as a ground cover, mow it short, apply a herbicide, and then cover it with 3” of mulch. You have to be vigilant and repeat the process several times. Any bit of leftover root or tendril will grow again.
To save any trees or your house structure, cut the ivy off about waist height. Pull down the climbing section, bag it, and dispose of it. Apply glyphosate herbicide to the remaining stump. Once the stump and most of the roots are dead, pull them out and dispose of them.
Privet
There are over 50 varieties of privet. They make excellent hedges but are difficult to control once established.
- Highly invasive. Crowds out native species. Taking over woodlands in the Eastern US.
- Form dense thickets with multiple trunks.
- Produce many berries. Seeds spread by birds.
- Very difficult to eradicate.
- Chinese and Japanese privet is considered an invasive species in many states.
Small plants can be pulled out–including the roots. Larger plants can be cut off and the roots dug out. Continually cutting off regrowth eventually kills the root. For truly effective removal cut the stump off at ground level and apply a herbicide to the stump.
Spraying the plant leaves with glyphosate (Roundup) usually kills the plant and roots. You may need to reapply the treatment in one year if it doesn’t kill everything. Once the plants are dead, remove the tree and root. (Glyphosate use is prohibited in some states and countries. The WHO considers it a probable human carcinogen.)
Barberry
There are several Barberry species–Japanese Barberry, Chinese Barberry, Korean Barberry, American Barberry, and European Barberry. They add beauty to gardens and can be used to improve health, make jams, and add taste to foods. They are also:
- Considered an invasive species in several states. Check local regulations before purchasing.
- Encourage ticks that can spread Lyme Disease.
- Out-compete local plants.
- Black stem rust fungus alternates between Barberry and cereal crops. It completes its sexual functions on the Barberry plant. The USDA has spent decades eradicating wild Barberry.
- After decades of eradication, Canada banned the importation of Barberry plants in 1966. It now allows a few species.
Non-invasive Barberry species–such as Crimson Cutie and Lemon Glow–are available.
Choose a time when they have no berries. Cut off bigger branches–then the main trunk. Treat the remaining stump with herbicide. Dig out the root stump. Don’t leave any part of the roots because they will regrow. Inspect the area regularly and dig out any sprouts.
This is a list of some of the worst invasive plants. It is by no means complete. There are dozens of invasive plants in North America that are dangerous, invasive, or annoying. Your personal experience with other species may be worse.
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