The 12 Most Difficult Weeds to Eradicate
Dealing with weeds is a frustrating, time-consuming, and inevitable part of gardening. While some are easy to get rid of, others can be a serious problem. Join gardening expert Melissa Strauss to identify some of the more difficult weeds to eradicate.
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What is a weed? By definition, it’s a wild plant that grows where it’s not wanted, and is usually in competition with cultivated plants. These plants, built for survival, are able to thrive in a wide range of conditions. They typically need no assistance to do so.
Some weeds, the native ones, tend to have their value in the local ecosystem. Many of them feed pollinators or provide food for wildlife. In their element, they sustain life, and they are adapted to thrive in those places with no intervention. Not all weeds are native, however, and even some of the ones that are can be frustrating.
These difficult weeds usually grow quickly, spread easily, and tolerate difficult conditions that would kill other plants. Many of them germinate and grow quickly, overtaking those they surround and depriving them of resources. Let’s talk about some of the most persistent and most difficult weeds in North America.
These are some of the most difficult weeds to eradicate, for various and exhausting reasons.
Field Bindweed
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botanical name Convolvulus arvensis |
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sun requirements Full sun to partial shade |
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height 2’-6’ |
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hardiness zones 2-10 |
Field bindweed is a plant in the morning glory family, and one of the most difficult weeds you may face. It’s delicate and pretty with white or pink flowers, but it’s a survival expert. It has a deep, extensive root system that can reach up to 20 feet deep. Even a tiny fragment of a root can regenerate a new plant.
This weed spreads by rhizomes and prolific seed production. The seeds remain viable for up to 50 years, which is an exceptionally long time. Pulling these up can create a bigger issue by leaving root fragments that grow into new plants. It’s also resistant to many herbicides. In addition to its other issues, field bindweed is poisonous.
What to Do:
Be persistent; you’ll need to treat it for several years in a row. Smothering can be effective, using thick mulch or weed fabric to block sunlight for entire seasons. Hand removal can work on small infestations if you catch them early. Dense ground covers that compete with it can help to reduce its energy over time.
Dandelion
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botanical name Taraxacum officinale |
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sun requirements Full sun |
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height 2”-24” |
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hardiness zones 2-12 |
We all know this one and can spot it from a mile away. The cheerful yellow flowers are actually great for pollinators, and the greens are tasty and nutritious. Dandelions are also one of the most tenacious lawn and garden weeds around. They can survive almost anywhere, and they’re perennial, so the same plant comes back each year.
Dandelions have a deep taproot, and even a small part of it left behind can turn into a new plant. Each individual flower can produce up to 200 seeds, and they travel far and wide on their tiny parachutes. They germinate, grow, and flower quickly, within weeks.
What to Do:
As soon as you notice young plants, pull them out. Make sure to pull only when the soil is damp so that the entire root comes out. Mowing will prevent spreading, but won’t kill the existing plants. However, this is a generally decent control. Dense turf grass will crowd out seedlings.
Chamber Bitters
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botanical name Phyllanthus urinaria |
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sun requirements Full sun to full shade |
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height Up to 2’ |
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hardiness zones 6-11 |
Chamber bitters are the bane of my gardening existence. I don’t remember when they showed up, but I know now exactly how tough they are to get rid of.
These warm-season annuals mature quickly. They also reseed aggressively. Tiny seed capsules form beneath every tiny leaf, and before you even know it, they drop those seeds everywhere.
One plant can produce hundreds of seeds in a season. They can go from seedling to flowering in about a month, and the seeds can live for several years. They will continue to germinate throughout the summer season, not just once a year. Every solid rain produces more plants, and the cycle is hard to break.
What to Do:
Mowing doesn’t help, and herbicides aren’t particularly effective. It’s best to pull them while they’re young, before they are two inches tall, if possible. If you are vigilant about removing them, in two or three years, you can eradicate them. A thick layer of mulch can help by blocking the light.
Canada Thistle
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botanical name Cirsium arvense |
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sun requirements Full sun |
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height 2’-5’ |
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hardiness zones 4-7 |
Canada thistles are notoriously one of the most difficult perennial weeds. The issue is their root system, reproduction method, and aggressive persistence. They grow from extensive underground rhizomes that grow up to ten feet deep and 15 feet horizontally. Tiny root fragments can form new plants.
These don’t just spread from roots; they reseed prolifically as well. A single plant can produce tens of thousands of seeds, and they remain viable in the soil for up to 20 years. Cutting and mowing don’t help, and Canada thistles are exceptionally tolerant of stress. It competes aggressively with nearby plants for resources.
What to Do:
Be persistent. It takes multiple years to eradicate this difficult weed. Repeated cutting, every two to three weeks during the growing season, can starve the roots. However, you have to do this consistently for two to three years. Herbicides are somewhat effective if you use them in late summer and early fall. Smothering can be effective, but do not till; this will make it worse by scattering root fragments.
Quackgrass
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botanical name Elymus repens |
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sun requirements Full sun to partial shade |
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height 1’-4’ |
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hardiness zones 3-12 |
Quackgrass is another difficult weed to get rid of. At first glance, it looks like ordinary turf grass, but it’s not. It quickly spreads out, choking other plants and surviving every removal attempt. It spreads through aggressive rhizomes that reach several feet in every direction. They are tough and brittle, and any small fragment can form a new plant.
This is a fast grower, and while rhizomes are the primary method of spread, they also produce seeds. Those seeds remain viable for several years and spread easily. Quackgrass is exceptionally tolerant of cold, heat, drought, and lack of nutrients. They are also tolerant of light deprivation.
What to Do:
Don’t pull or till, as pieces of rhizome left behind will split and grow into new plants. Herbicides aren’t particularly effective, and mulching is typically ineffective. You can smother them over time with thick tarps. It takes an entire season to do this. Targeted herbicides can be useful, but you must apply them repeatedly. Consult your local extension office and follow the label if you choose to go this route. Some dense ground covers can outcompete it.
Pigweed
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botanical name Amaranthus retroflexus |
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sun requirements Full sun |
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height 3’-6’ |
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hardiness zones 3-11 |
Pigweed ranks among the most difficult weeds to eradicate for several reasons. It’s incredibly aggressive and can take over spaces quickly. When it comes to seed production, this weed takes the cake. A single plant can produce up to 500,000 seeds in a single season. The seeds also remain viable for up to 40 years.
Pigweed is a fast grower and can go from germination to seed production in as little as one month. Hot weather speeds the process. It’s not bothered by heat, drought, or lack of nutrients. It’s also resistant to herbicides, and seeds germinate in multiple flushes throughout the season.
What to Do:
Mowing and cutting don’t work. Tilling just buries the seeds deeper, and one-time herbicide use won’t cut it. Pull seedlings when they are under two inches tall. Prevent seed production at all costs. Using cover crops will help to reduce open soil exposure.
Lamb’s Quarters
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botanical name Chenopodium album |
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sun requirements Full sun to partial shade |
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height 3’-10’ |
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hardiness zones 2-11 |
Lamb’s quarters is also called wild spinach, because it is a nutritious, edible plant. That’s where the perks end, though, as it is one of the most difficult weeds in the garden. It’s fast-growing, and a single mature plant can produce 70,000 seeds in a season. The tiny seeds travel easily and can remain viable in the soil for up to 40 years.
Seeds germinate in more than one flush, and the plant can grow as much as an inch per day. It thrives in just about any soil type and shades out other plants. It’s tolerant of heat, drought, and a wide range of pH levels. It germinates early, so it’s difficult to crowd it out.
What to Do:
Remove it early, when it’s less than four inches tall. Never let it go to seed. Mulch heavily to deprive it of sunlight, and monitor it for the entire season. One-time control is not enough, and pulling it late allows it to go to seed.
Nutsedge
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botanical name Cyperus rotundus |
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sun requirements Full sun |
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height 6”-48” |
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hardiness zones 3-10 |
Nutsedge looks like grass, but it’s not. It’s a sedge, and it’s one of the most difficult weeds to deal with in lawns, gardens, and fields.
Its resilience, reproduction, and resistance to control are what make this one hard to manage. Nutsedge spreads through tubers on its rhizome. It can produce hundreds of them in a season.
The rhizomes spread several inches per week, and they can pop up through mulch, dense turf, and plastic. It’s incredibly difficult to get rid of all the tubers, and it thrives in both wet and dry conditions.
What to Do:
Pulling and tilling don’t work because they don’t remove the tubers, and they break up the roots to create new plants. Mowing doesn’t work, and herbicides don’t kill the tubers.
Targeted herbicides made for sedges can be effective. Mulching heavily is helpful, but the best way to get rid of them is by carefully digging up as much of the rhizome and tubers. Watch for re-growth and remove new plants before they produce tubers.
Creeping Charlie
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botanical name Glechoma hederacea |
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sun requirements Full sun to full shade |
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height 4”-16” |
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hardiness zones 3-10 |
Creeping Charlie, or ground ivy, is one of the most stubborn and difficult weeds because of its aggressive spreading. It’s also resistant to most controls, and once established, it is relentless. It spreads in three ways. It produces above-ground runners, creeping underground rhizomes, and seeds as well.
Any small amount of root left underground can regrow a new plant, so breaking the roots apart is counterproductive. It can outcompete turf grass and just about anything else. It doesn’t mind shade, compacted or poor soils, and survives mowing and drought. It’s also fairly resistant to herbicides.
What to Do:
Overseed your lawn to reduce compaction and crowd out the creeping Charlie. Loosen soil and remove as much of the root as possible when you can. Use broadleaf weedkillers in the fall and spring, and use thick landscape cloth and mulch to suppress growth.
Poison Ivy
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botanical name Toxicodendron spp. |
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sun requirements Full sun to partial shade |
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height 1’-4’ |
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hardiness zones 2-11 |
Poison ivy is one of the most difficult weeds, not only because of its persistence, but because of the health risks it poses. It’s perennial and spreads aggressively if not controlled, persisting for years. It grows as a vine, a shrub, and a groundcover.
Poison ivy has deep, tough, woody roots, and small fragments can regenerate new plants. They spread laterally, and plants can pop up far from the parent. It reseeds, and birds eat the seeds, so they can turn up anywhere. Pulling can cause a terrible rash, and burning it is even worse.
What to Do:
Always protect your skin and eyes when dealing with poison ivy. If possible, dig up the entire root system of small plants. You can cut the stem at the ground and apply herbicides right away; repeated use may be helpful.
Molucca Bramble
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botanical name Rubus moluccanus |
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sun requirements Full sun to partial shade |
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height 7’-19’ |
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hardiness zones 9-11 |
Molucca bramble is related to raspberries and blackberries, and is a seriously invasive weed in many places. It’s particularly difficult in hot, humid climates. Brambles in general are difficult to eradicate, largely due to their thorns, and this one is no exception.
It has a deep, woody crown that sends out a network of spreading roots. The roots can send up suckers far from the crown and form additional thickets.
The canes that make up the above-ground portion of the molucca bramble are long, and when they touch the ground, they root at the tips. They also produce berries that animals enjoy eating, and they disperse the seeds in their droppings.
What to Do:
The canes are dense and prickly, which makes removing them difficult. They regrow rapidly as well. Mowing and cutting simply encourage faster growth and spreading. Cut and paint is effective. This involves cutting at the ground and applying targeted herbicides. Removal of the woody crown is also effective in small infestations. Monitor and prevent the spread for two years by cutting away any fruiting canes.
Ragweed
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botanical name Ambrosia spp. |
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sun requirements Full sun |
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height Up to 17’ |
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hardiness zones 2-11 |
Ragweed is one of the most common seasonal allergens and one of the most difficult weeds to eradicate. It’s stubborn and highly competitive.
Its competitiveness comes from its massive seed production. One plant can produce tens of thousands of seeds in a season. They are small and easily dispersed, not to mention that they can remain viable for up to 40 years.
It germinates later in the year, so it’s often missed by early mitigating processes. It’s a fast grower and develops deep tap roots, so it’s a survivor in tough climates. Ragweed can grow in just about any circumstances, and one-time removal doesn’t address the seed bank issue.
What to Do:
Target seedlings early, before they are four inches tall. Mow repeatedly to keep them from going to seed. Mulching and cover cropping can be effective, as shade reduces germination. You’ll need to work at controlling it for several years because of the seed bank.
