Three-cornered leek identification

Read through our Three-cornered leek identification guide below. If you are still not sure, email us your photos and we’ll confirm whether it’s Three-cornered leek for FREE.

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What does Three-cornered leek look like?

Three-cornered leek (Allium triquetrum) is a perennial bulbous plant in the Alliaceae family, commonly known as the onion family. Referred to by alternative names such as “Three-cornered garlic” and “Angled onion”, this species originates from the Mediterranean region but has extended its presence globally, particularly gaining invasive status in the UK.

Its name is derived from the unique triangular structure of its stem. Characterised by narrow, three-angled leaves, the plant bears white, star-shaped flowers arranged in clusters resembling an umbrella at the apex of the stem. Emitting a distinct garlic or onion fragrance, Three-cornered leek is edible. All parts of the plant, including the leaves, flowers, and bulbs, have a mild garlic or onion flavour. It is often foraged and used in culinary dishes, adding a subtle and unique twist.  However, exercising caution is crucial when foraging for this plant, given the potential for confusion with toxic counterparts like bluebell bulbs.

Is Three-cornered leek an invasive plant?

Yes, Three-cornered leek is considered an invasive species in many regions. Native to the Mediterranean region, it has become a problem in the UK. The invasive characteristics of Three-cornered leek include rapid reproduction, both by seed and bulb division and adaptability to a wide range of environmental conditions, thriving in a wide range of environments. 

Like many other non-native invasive plants, Three-cornered leek is detrimental to ecosystems.

The plant not only outcompetes native plant species for resources but also alters soil composition, through the decomposition of its leaves, reducing biodiversity.

Also, Three-cornered leek may be edible, but its nutritional value for wildlife may be limited compared to native plant species. This could impact herbivores and invertebrates alike, which may rely on diverse plant sources for nutrition.

Those negative ecological impacts of Three-cornered leek highlight the importance of managing and controlling this invasive plant species to preserve health and diversity of ecosystems in the UK.

What does Three-cornered leek look like in autumn?

In autumn, Three-cornered leek undergoes a noticeable transformation as part of its natural growth cycle. The strap-like leaves, often exhibiting a three-angled structure, begin to wither and die back during this season. The vibrant green foliage of the plant gives way to hues of yellow and brown, showing the approach of winter. As the leaves deteriorate, the plant redirects nutrients from the foliage to other vital parts, and this process is a crucial preparation for the colder months.


How do you identify Three-cornered leek in the winter?

As winter progresses, the strap-like leaves of the plant, which may have withered and turned yellow or brown in the preceding autumn, typically die back completely. The above-ground foliage recedes, leaving the plant in a more dormant state during the colder months. The visible signs of life become subdued as Three-cornered leek prepares to endure the winter chill.

While the above-ground parts of the plant may appear dormant, the below-ground bulbs play a crucial role in the winter survival strategy of Three-cornered leek.

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How does Three-cornered leek grow?

  • Three-cornered leek starts its life cycle as a bulb. The bulb contains the necessary nutrients for the initial stages of growth. Under favourable conditions, the bulb germinates, and the first shoots emerge from the soil.
  • As the plant establishes itself, it produces strap-like leaves that are often three-angled, giving the plant its name. The leaves grow in a basal rosette, forming a cluster close to the ground. These leaves are green and contribute to the plant’s ability to photosynthesise and produce energy.
  • Three-cornered leek typically flowers in spring and early summer. The plant produces tall stems with umbrella-like clusters of small, star-shaped white flowers. The flowers are arranged at the top of the stem, adding an ornamental quality to the plant.
  • Following pollination, Three-cornered leek produces small, black seeds. The seeds develop within the flower structures and contribute to the plant’s reproductive strategy. Seed production is one of the ways in which Three-cornered leek spreads and colonises new areas.
  • The mature seeds are dispersed by various means, including wind, water, and human activities. This dispersal mechanism enhances the plant’s invasive potential, allowing it to establish itself in diverse environments.
  • Three-cornered leek also reproduces vegetatively through bulb division. The bulbs multiply, giving rise to new shoots and allowing the plant to spread within its habitat. This method of reproduction contributes to the plant’s ability to form dense colonies.
  • In winter, above-ground parts of Three-cornered leek may die back, and the plant enters a period of dormancy. However, the bulbs beneath the soil remain active, storing nutrients and energy to support the plant through the colder months.

Interesting facts about Three-cornered leek

  • Introduced to the UK from The Mediterranean region, including Spain and Portugal, in the 19th century, when many exotic and non-native species were brought over for botanical gardens, Three-cornered leek has recently become problematic.
  • Three-cornered leek was reportedly used as part of Greek and Roman mythology and religious festivals as it was believed that the plant had purifying properties.
  • When crushed or bruised, the plant gives out a strong garlic or onion scent. This aroma is a common feature of many plants in the Allium genus, which includes onions, garlic, and chives.
  • Three-cornered leek is edible. The plant has a mild garlic or onion flavour, and its leaves, bulbs, and flowers are sometimes used in culinary applications. However, caution is advised, as it can be easily confused with toxic plants like bluebell bulbs.
  • It is an offence under Schedule 9 of the Wildlife and Countryside Act in England and Wales to plant or otherwise cause to grow this species in the wild.
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Is Three-cornered leek a problem?​

In short, the answer is Yes!

Just like other invasive plants, Three-cornered leek is extremely resilient, meaning it can grow pretty much anywhere, regardless of the soil or weather conditions.

The robust growth of the plant raises environmental concerns as it outcompetes native plants, causing imbalance in ecosystems. Its invasive nature leads to habitat disruption, adversely affecting biodiversity and constraining resources available to native flora and fauna. The absence of natural predators, coupled with its formation of dense colonies, amplifies the potential harm it poses to the local environment.

This is why the plant is currently under Schedule 9 of the Wildlife and Countryside Act in England and Wales, meaning it is an offence to plant or otherwise cause to grow this species in the wild.

What can you do?
Three-cornered leek removal methods

Once established, Three-cornered leek can become a real nuisance and can be difficult to remove. Large areas can be effectively tackled by a professional invasive weed company, which will use various tactics dependant on the size of the infestation and requirements of removal. As the plant is listed on the Wildlife and Countryside Act, all plant material and associated soil that may contain seeds or bulbs is classed as controlled waste and can only be removed by a licenced contractor to an authorised waste facility.

  • Hand pulling.
  • Mulching.
  • Herbicide application.
  • Excavation.


Depending on the size of infestation, multiple techniques can be undertaken to control or eradicate Three-cornered leek from your property.

Find out more by visiting our Three-cornered leek removal page.

Start fixing your invasive plant problem today by requesting a survey

Rest assured, where invasive species are identified at an early stage and tackled correctly, problems can usually be avoided. Our specialist consultants complete thorough surveys to identify the extent of the problem. Our plans aren’t one-size-fits-all; they’re customised to tackle the invasive species at your property effectively, taking account of all of your requirements. 

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