Have tall stalky weeds invaded your garden? Most weeds are easy to spot, especially if you maintain your garden or yard.
However, tall weeds are another thing altogether. Due to their height and thick stalks, they look like actual trees. As such, you are likely to let them continue growing.
But make no mistake! Despite their appearance, large weeds that look like trees can be highly invasive. If left to grow, you risk creating an uncontrolled infestation in your garden.
On top of that, some of these plant-like weeds can be very aggressive – by depleting nutrients for your garden plants.
It is, therefore, necessary to identify any unknown giant weeds growing in your garden. You can choose the most appropriate solution for eradicating them by doing so.
Below, we have compiled a list of some of the most common tall weeds with thick stalks you will likely encounter in your garden.
1. Paulownia tree (Paulownia tomentosa)
The paulownia tree, also known as the princess or empress tree, is a fast-growing plant from the Paulowniaceae family.
The plant is native to Asia and was introduced to other parts of the world for its ornamental benefits. However, it is considered an invasive weed due to its fast growth.
Paulownia is a tall-growing plant, one of the tall weeds that look like trees – it can reach as high as 30 meters when mature. It has large leaves and a thick stalk even when young.
Another distinguishing feature of the empress tree is its flowers – there aren’t many tall weeds with purple flowers.
2. Pokeweed (Phytolacca Americana)
Pokeweed, also known as American pokeweed, is a perennial weed that is common in the North American region and Europe, and Asia.
It is an invasive weed with an extensive taproot system, making it challenging to eradicate. The plant is also highly poisonous to humans, animals, and pets.
Pokeweed is a tall-growing plant – reaching up to 10 feet. It is one of the most common weeds with thick herbaceous stalks.
As such, it resembles a shrub or a young tree. You can identify the weed by its reddish stem, small, white flowers, and green, lance-shaped leaves.
Another unique feature of the weed is its berries. When unripe and young, the fruits are green. As they mature, they turn into a dark shade of purple.
3. Bittersweet nightshade (Solanum dulcamara)
Bittersweet nightshade is an herbaceous, perennial vine plant. It grows in a wide range of areas, from gardens to hedges, marsh areas, woods, and other areas.
It is not considered a weed in some areas but can be invasive – spreading through seeds, creeping stems, and root systems.
Bittersweet nightshade is a high-growing tree that can reach up to 30 feet tall. It tends to climb over small trees, shrubs, and plants. Its branches can also grow low, forming a horizontal thicket.
Bittersweet nightshade has large, green leaves with purple tinges. It produces purple flowers (blooming around May to September) with a yellow stamen.
The weed plant also bears egg-shaped berries, which turn from green to orange and then red as they ripen.
4. Castor bean (Ricinus communis)
Castor bean plant, also known as the castor oil plant or Ricinus is a tall, fast-growing shrub-like plant. It is native to the African and Asian regions but has spread worldwide – introduced to new areas as an ornamental plant.
Ricinus plant grows pretty high, reaching heights of 12 meters. It has a thick stem with a purple-to-reddish color. It also sports huge leaves, whose shape appears like an open palm.
The leaves are shiny and have a dark reddish or purple color, which transforms into dark green as the plant matures.
Castor oil is not considered a weed in some areas and is even grown for its beauty or medicinal properties. However, it can establish itself in a place and become invasive.
Furthermore, the highly toxic plant produces a poisonous ricin compound that can seep into the soil and interfere with other plants.
5. Japanese knotweed (Reynoutria japonica)
Japanese knotweed, also known as Asian knotweed, is an herbaceous plant originating from the Polygonaceae family (knotweeds and buckwheat). It is native to Asia but is found worldwide, particularly in Europe and North America.
The Japanese knotweed is one of those tall weeds with thick hollow stalks that can reach up to 4 meters high. The stems are green in color and have raised nodes – just like in bamboo stems.
The leaves are large, green, and heart-shaped but with a truncated base. In the summer and fall seasons, the weed also produces small, white, or cream flowers that shoot from upright stamens.
If you find this weed in your garden, follow this removal guide if you prefer natural methods or use any of these chemicals.
6. Western dock (Rumex occidentalis)
The western dock is a flowering plant that is native to the North American region. It is perennial, grows from a robust taproot system. It has medicinal uses, and the leaves and stems are both edible.
Western dock grows primarily forms a single, upright, reddish-brown stem that can reach up to 6 feet. The leaves are bright green, triangular, and blade-like in shape and have a truncated base.
They are somewhat similar to curly dock weed, except it is longer, pointed at the apex, and not as wavy. Instead, they are pretty identical to leaves from some species of spinach.
While the western dock plant is pretty beneficial, letting it grow in your garden might not be the best idea. It produces several seeds, which can cause a massive infestation.
It is also tough and can resist harsh climatic conditions once it reaches maturity. Therefore, if unchecked, eradicating it can be a monumental task.
7. Wild lettuce (Lactuca virosa)
Wild lettuce is the common name given to several lettuce species closely related to cultivated lettuce.
The most common of these species is the Lactuca virosa plant, which goes by several local names – bitter lettuce, opium lettuce, and great lettuce, among others.
Wild lettuce is native to Africa (northern regions), Asia, and Europe but has naturalized worldwide. It is one of the large weeds, reaching heights of up to 2.5 meters.
It has a single, thick, erect stem, which becomes pretty robust as the plant matures. The stalk is green in color but can range from brownish red, greyish green, and purple, depending on the species.
You can also identify wild lettuce by its leaves. They are green in color, thick, and elongated. They also have serrated edges and a strong vein along the midline.
The plant produces a white sap with analgesic and sedative properties, hence the opium lettuce.
8. Butterfly bush (Buddleia davidii)
Butterfly bush is a fast-growing flowering plant native to Asia and the Americas but common in most parts of the world.
It is a deciduous plant with arching bushes that can reach up to 15 feet. Therefore, it is one of those weeds that look like small trees.
Butterfly bush has green hairy stems when young and grey-brown and peeling as the plant matures. The leaves are dark green to blue-grey and usually have short hairs on the underside.
However, the most distinctive feature of the weed is its flowers. It produces showy flowers that grow spikes at the stem’s end.
They come in various colors, from pink to white, dark purple, orange, and yellow.
Butterfly bush can be cultivated as a flowering plant due to its attractive blossoms. However, it is an aggressive plant that can tolerate harsh conditions. If uncontrolled, it can overcrowd and overwhelm native plants.
9. Indian Hemp/dogbane (Apocynum cannabinum)
Hemp dogbane is a herbaceous perennial plant that is common in North America – throughout the US and southern parts of Canada.
It is a highly poisonous plant, particularly to dogs and livestock, but it can even be fatal if ingested by human beings.
It goes by several local names – Amy root, Indian hemp, Indian psychic, and rheumatism weed. The phrase “hemp” is used due to its similarity to the cannabis plant as a source of fiber – it does not have psychoactive properties.
Hemp dogbane is a large weed plant that grows as high as 2 meters. These weeds have thick, reddish stalks and produce a milky sap that can cause skin irritation. Its leaves are large, lanceolate-shaped, and grow in an opposite formation.
They are green in color with a smooth top surface and hairy underside. Hemp dogbane also produces large white flowers that bloom during summer.
10. Creeping thistle (Cirsium arvense)
Creeping thistle is a perennial flowering plant native to Asia, Europe, and northern parts of Africa.
However, it has been introduced to several regions worldwide for its ornamental properties. The plant goes by several local names, such as California thistle, corn thistle, field thistle, and Canadian thistle.
Creeping thistle is a tall, herbaceous weed plant that can grow up to 150 cm high. The plant starts growing in a basal rosette formation before transforming into upright, branching stems.
The creeping thistle produces dark green, oblong-shaped leaves that grow in an alternate formation on the stem. They have irregularly shaped edges, which are spiny.
The upper part of the leaves is smooth, while the underside is hairy. Another feature of the plant is the small, pink to purple flowers, which form at the top of the stems.
Creeping thistle is an aggressive weed plant that can invade pastures, fields, and gardens. It spreads quickly through seeds and its creeping tap root system.
On top of that, it is pretty tough and can withstand harsh climatic conditions, not to mention that it is resistant to most herbicides.
11. Wild sunflower (Helianthus annuus)
Sunflowers are not considered to be a weed by most people. They are grown commercially for oil, have aesthetic flowers, and even extract toxins from the soil.
However, despite these benefits, wild sunflowers can be pretty aggressive. They have a rapid root expansion and thus can spread very fast.
They are also very competitive and can be resistant to herbicides. Therefore, they can be a nightmare, especially if they start growing in crop fields and gardens.
The wild sunflower is a bushy plant that grows up to three meters tall with stout, hollow stems. It has greyish-green leaves, which grow in an alternate formation from the stem.
They are ovate to orbicular in shape, large (up to 10 cm long), and have toothed margins and fine hairs.
You can also identify the plant with its large, conspicuous yellow flowers with a sun-like shape – hence the name.
12. Giant hogweed (Heracleum mantegazzianum)
Giant hogweed is a perennial flowering plant native to Eurasia but was introduced to several parts of the world as an ornamental plant.
It is considered to be a noxious weed in most places – it spreads very fast, overcrowding other plants, and produces a toxic sap that is toxic to human beings.
Giant hogweed is one of the big weeds – hence the name – with the potential to reach up to 5.5 meters high. You can identify it by its thick, green stalks with purple blotches and coarse hairs at the base from where leaves emerge.
It also has large, deeply incised, and loved leaves that grow in an alternating pattern.
However, its most unique feature is the large white flowers, which form an umbrella-like design at the top of the plant.
13. Thickhead (Crassocephalum crepidioides)
Thickhead is a herbaceous weed plant that is native to sub-Saharan Africa but widespread worldwide.
It goes by several local names, such as fireweed, redflower ragleaf, and hawksbeard velvet plant. It primarily grows in crop fields, forestry plantations, gardens, parks, roadsides, waster areas, etc.
The thickhead weed plant has tall-growing, erect stems that grow up to 1.5 meters high. They can be hairless or have small amounts of hair.
Leaves shoot out from the stem in an alternate formation, and they can grow pretty huge (up to 20 cm long and 10 cm wide). These leaves are ovate-shaped, have a toothed margin and a pointed apex, and are usually lobed.
The final identifying feature of the thickhead weed is the flowers. The plant produces clustered flower heads, which grow at the top. They range in color from orange to reddish, purple, or pinkish.
14. Common mullein (Verbascum thapsus)
Common mullein, also known as the great mullein, is a biennial plant native to Africa, Asia, and Europe. It commonly grows on roadsides, hedgerows, railroads, pastures, gardens, meadows, and more.
Common mullein is not considered highly aggressive; it is not as competitive against other plants. It is also easy to eradicate using mechanical (hands) or chemical (herbicides) solutions.
That being said, it produces several thousand seeds and has a deep taproot system. As a result, it has the potential to spread very fast, becoming quite a nuisance.
As one of the most common weeds with thick stalks, the common mullein grows in a single upright stem that reaches up to two meters. It has large, oblong-shaped leaves that reach up to 50 cm long.
They grow in rosette formation during the first year, and after that, they grow in an alternate shape.
The plant’s leaves are greyish-green in color, with a smooth upper side and a hairy underside. Besides that, you can identify common mullein by its small, yellow flowers that group densely in a spiral formation up the stem.
15. Himalayan balsam (Impatiens glandulifera)
Himalayan balsam is a large annual flowering plant native to the Himalayan region. However, it spread to several areas after being introduced as an ornamental plant.
Himalayan balsam is considered to be an invasive plant in several areas. It is aggressive, proliferating quickly through seed dispersal (one plant can produce up to 800 seeds). It is also very competitive and tends to crowd out and out other vegetation.
Himalayan balsam is a tall-growing weed plant that reaches up to 3 meters high. It has large, broadleaf leaves (up to 23 cm long), lanceolate-shaped.
They are bright green and shoot out from the red-tinged stem. The plant also produces a cluster of pink to purplish flowers, which bloom between June and October.
The above are some tall weeds with thick stalks that you can find in your garden. Hopefully, they can help you identify the plants you are dealing with and whether they are invasive or not.
However, several more weeds fit the criteria. If the plant you are dealing with is not in the list above, there are a few other ways of identifying it.
For example, you can look up its features (stem, leaves, and flowers) on the internet. You can also take a picture and use a plant identification app to find its name.
IW’s Chief Editor and a lover of green spaces.