When you find tall weeds with thick stalks on your land it’s important to identify them.
Some weed species are invasive and spread quickly, crowding out other plants.
If left unchecked, they can take over your yard. And they’re very hard to get rid of.
Once identified, you can plan an effective method of control.
So in this article, we take a look at 11 of the most common types and how to recognize them.
Ambrosia trifida by Frank Mayfield
This annual weed is a North American native that’s found in many parts of the US, Canada, and Northern Mexico. You can also come across it in Europe and Asia where it’s an introduced species.
It’s widely considered to be a noxious weed. And it’s destructive to other plants in the areas it invades as it outcompetes them for sunlight and puts them in the shade.
This is a tall plant that grows between 3-12’ tall with occasional branching. The thick green stem has a coating of fine white hairs. And the large leaves have 3-5 lobes and grow up to 12 inches across.
The upper stems end in a spike of small yellowish-green flowers arranged in drooping clusters around the spike.
Seed dispersal occurs through spiky burs that people, animals, and water, carry to new locations.
Giant ragweed produces a large amount of fine pollen that’s spread easily by the wind. It’s a significant allergen that affects hayfever sufferers.
You might hear American pokeweed referred to by a variety of names, including phytolacca Americana, poke sallet, and dragon berries.
It’s a perennial weed that’s native to the Gulf Coast, midwest, and the eastern US. And it’s naturalized in some parts of Asia and Europe.
The plant grows tall, usually between 4-10 feet. And produces deep reddish-purple berries that are poisonous to people, pets, and farm animals. But birds like to eat them and are responsible for spreading the seeds.
You can easily identify the plant by its berries. But if it’s not carrying fruit, then look for its thick green-purple stems, green leaves with long petioles, and green-white flowers.
It’s usually thought of as an invasive weed. It forms dense bushes and spreads rapidly. Taking over and affecting the growth of other plants.
Some horticulturlists plant pokeweed as an ornamental. But if you have children, you need to be particularly careful about growing this weed in your garden. The berries may look very attractive, but they can be fatal if you eat them.
As the name suggests, this large perennial plant is native to Japan, as well as other East Asian countries such as Korea, China, and Taiwan.
It was introduced to Europe and the US in the 19th century. And became popular as an ornamental plant because of its bamboo-like appearance and ease of growth.
Japanese knotweed is difficult to identify when young due to the similarity of its stems and leaves with a number of plants.
But it’s easier when it’s mature. The thick stems are hollow and you’ll clearly see the raised nodes. The stems grow tall, and the plant can reach up to 10 ft. when fully grown.
Growing out from the nodes are green shovel-shaped leaves with a pointed tip. The plant comes into bloom in late summer/early fall, and produces small creamy white flowers.
Japanese knotweed is an invasive plant that spreads rapidly through rhizomes once established. Many US states consider it a noxious weed because it crowds out and displaces native plants.
Giant hogweed is a perennial flowering shrub that originated in the western caucasus region of Eurasia, but has now spread around the world. First as an imported ornamental plant. And now as a noxious weed.
In the right conditions the plant can grow 18 ft. tall. With a stiff tall stalk that grows up to 10 cm thick and 13 ft. high. When it blooms, you can see multiple clusters of white flowers growing from short stalks up into the air. They grow out from a central point, resembling an umbrella.
A fully grown plant has gigantic, deeply lobed leaves that can grow up to 5 ft. wide.
It’s sometimes mistaken for similar looking plants such as cow parsnip, woodland angelica, purplestem angelica, lovage, valerian, and Queen Anne’s lace.
But giant hogweed grows much taller than any of these. And the stalk has reddish-purple spots and coarse bristles. None of the lookalikes have both of these.
You should wash your hands immediately if you touch hogweed. The watery sap is phototoxic and can cause serious burns if you expose your skin to sunlight.
Common mullein is a biennial plant that’s indigenous to North Africa, Asia, and Europe. It’s also been introduced to Australia and the US.
In it’s first year of growth it develops a rosette of leaves 1-2 feet across. And then in the second year the flowering stem grows, sometimes reaching over 7 ft. in height.
Other distinguishing features include a hairy stem. And large velvety leaves that can grow to 15 inches long and 5 inches across. The leaves are oval and covered with short hairs.
A highly visible spike at the top of the stem is densely packed with 5 petalled yellow flowers.
Common mullein spreads by seed. Forming a dense ground cover that displaces native plants and wildlife.
It’s considered to be invasive in some US states.
There are many different types of wild lettuce. But the two you’re most likely to come across are Lactuca serriola and Lactuca virosa.
The plant is a biennial or annual herb. It’s also considered to be a weed.
Originally a native of North Africa, Europe, and Asia, it has spread to many parts of the world.
When it’s young, wild lettuce is sometimes confused with a common weed type: the dandelion plant. It’s a member of the same family and has a similar rosette.
But when it’s fully mature, you can find it growing 7-8 feet high in suitable conditions. The thick, strong stem sometimes has a covering of slender prickly spines. And the stem color varies in species between green, brownish-red, and purple.
The green leaves are long with deep notches and spines along the central vein on the underside.
The plant produces a milky sap that some people use for its sedative and analgesic properties.
Creeping thistle gets its name from its creeping lateral root growth that allows it to quickly spread and form dense clumps
It’s an upright herbaceous perennial weed that’s native to Europe, North Africa, and Western Asia. But it’s now found widely around the world in suitable climates.
It was introduced to the US in the 17th century. But 43 states now consider it a noxious weed.
The plant grows up to 5 ft. high. And as its root system expands, it sends up vertical shoots and forms vast clonal colonies.
The thick green stalks are smooth and branched. And the dark green leaves are lobed and covered in sharp spines. The leaves can grow 20 cm long and 3 cm wide, and are larger lower down the plant than on the upper part.
The distinctive flowers are pink-purple and consist of numerous small petals.
It’s aggressive root growth, along with prolific seed production and dispersal, make this a very difficult weed to control.
This large annual herbaceous plant is well known for its flowers and seed production.
But would you recognize it without the impressive flower head?
If not, you can also identify it by its long, thick stem, that grows upright and is coated with fine hairs. As well as the large, green, heart-shaped leaves.
Sunflowers are part of the genus Helianthus which contains about 70 plant species. And sunflowers come in many varieties of varying size and flower appearance.
Birds spread the seeds, so you might sometimes find one growing unexpectedly in your garden. And some people like to plant them as ornamentals in landscaping.
A native of Asia and Africa, ricinus is now grown worldwide as an ornamental plant.
Also called castor oil or castor bean plant, it’s a fast-growing perennial shrub. And when mature, it can grow about 12 ft. tall in the right climate.
As well as its attractive appearance and commercial uses, it’s also well known for containing the deadly poison ricin. You can find this in all parts of the plant, but especially in the seeds.
It’s easy to identify ricinus:
It has a purple-red thick stalk. And big leaves with between 5-11 fingers. The leaves are glossy, and change in color from dark red-purple on a young plant, to dark green as the plant grows and matures.
The fruits are also distinctive. They have a spiny capsule that’s either red or green in color. With each capsule containing the large, bean-like — and highly dangerous — seeds.
Himalayan balsam is an annual herb that’s also known as copper tops, policeman’s helmet, gnome’s hatstand, Indian Jewlweed, and touch-me-not.
As the name suggests, it’s native to the Himalayan mountain range. And more precisely, to the area between Uttarakhand and Kashmir.
It was introduced in the 19th century to Europe and North America as an ornamental plant. But it’s now often considered an invasive plant.
It grows in a range of soil types. But you’re most likely to find it along the banks of rivers and streams. You can also come across it in wetlands, forests, and roadsides. Sometimes, you might even find it growing in your lawn grass.
Himalayan balsam grows up to 6-7 ft. tall. The red-purple stems are smooth and hollow. And they thicken as the plant grows to maturity. There are 5-10 pink or white flowers on each stem, with each flower having 5 petals. Each leaf is large, oval, and pointed at the tip.
The ripe seed capsules are fragile and explode when touched, spreading seeds for several meters. This has earned the plant the alternative name of touch-me-not.
It spreads quickly in areas it infests. Densely covering an area and crowding out the indigenous vegetation. This reduces biodiversity in the area.
The paulownia tree is a native of China. But it’s now found in many parts of the world as its often used as a decorative plant in landscaping.
It’s particularly fast growing, expanding up to 5 meters in a year. And in some parts of the US it’s thought of as an invasive plant
If you find this weed tree growing unexpectedly in your yard you can identify it by its large flat green leaves and tall, thick stalk.
The mature tree grows up to 25 meters tall. And it’s impressive when in bloom, with it’s pink-purple flowers and vanilla fragrance. But when it’s a sapling, it’s easy to mistake it for a large weed.
Other names for the tree include empress tree, princess tree, and foxglove tree.
How Do You Get Rid Of Tall Weeds With Thick Stalks?
You can kill tall weeds with thick stalks by applying a post-emergent systemic weed killer.
First, cut the stalk of the weed so that you only have about 8 inches left sticking out from the ground. Make sure you collect the plant material in a bag for disposal as some weeds can reroot.
Then apply the weed killer to the stump and to any remaining leaves. The weed killer will be absorbed by the plant and travel down to the roots, killing all parts of the weed from the inside.
It’s important to use a herbicide that can kill to the root because otherwise the weed will regrow.
If you prefer to do things the natural way then you can try to pull the weed by hand. But this can be very challenging. The problem?
You often need to remove all parts of the weed to prevent it from growing back again. And some plants have very extensive root and rhizome systems.
Some weeds, such as Japanese Knotweed, can be very difficult to completely eradicate yourself. You can try using the best commercial grade weed killer. But you may need to hire a professional service to take care of the problem if the area is overgrown.