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Gunnera, commonly called Giant Rhubarb or Gunnera Tinctoria is an invasive non-native species in Europe that is threatening the native habitats and gardens. It was first introduced to gardens in England from Chile in the 20th Century and between 1930 and 1980 it became naturalised in southwest England, on the coast of Scotland, on the west coast of Ireland, and spread further to the coasts of California and New Zealand.

Is Gunnera Invasive in the UK, and why remove the flowers?

Is Gunnera Invasive in the UK, and why remove the flowers?

Giant rhubarb is a large-leaved plant and a popular ornamental garden choice. It grows rapidly in temperate regions and frost-free habitats with moderate rainfall. It spreads easily through trimmed, discarded rhizomes and seeds dispersed by birds during the pollination process.

With its vigorous spread and rapid growth, it presents itself as a threat to the native vegetation of the area, so yes, Gunnera is an imvasive plant in the UK and other areas. 

To reduce the threat of native plants and reduce the spread of Gunnera, a European-wide ban was placed on the sale and further cultivation of the plant. However, if you cultivated this plant before the ban, you may keep it as long as it doesn’t spread outside your boundaries. Gunnera is not poisonous and is non toxic to dogs.

Are Gunnera roots invasive?

Gunnera plant grows best when planted close to water, but they can thrive in drier conditions because their roots are capable of penetrating the soil up to 1 metre deep. If you want to divide gunnera read here. The depth to which the roots grow and the growing and spreading characteristics of the plant are some of the reasons why gunnera roots are considered to be invasive

They spread quickly through their root system so trimmed rhizomes and fragments of broken roots can sprout entirely new and healthy gunnera plants. 

How do I get rid of Gunnera?

There is no simple, singular method to get rid of gunnera. Most of the removal methods have to be repeated continuously to ensure the effects are nearly permanent. Regardless of the control method you use, always check back for regrowth and seedlings seasonally and continue the treatment as necessary. The most common methods to get rid of gunnera are discussed below.

  • Chemical Control
  • Stump treatment: Herbicide can be applied as a stump treatment especially when the Gunnera plant is too close to water or other useful plants. Simply cut all the leaves of the plant to just above ground level then apply the herbicide around the exposed wounds and use the cut leaves to cover the herbicide wounds to protect them from rain and the weather. Discard the remaining leaves and seed heads in a recommended manner to avoid regrowth in other surrounding spots. 
  • Spraying: Though stump treatment usually uses more concentrated chemicals to form the herbicide than spraying which just needs more volume of the herbicide, it is considered the most effective method. Spraying, however, requires calm weather because a storm 24 hours after application will render the herbicide ineffective. After spraying, the entire plant needs to be wrapped up until liquid begins to run off, this will prove that the plant is dying away as intended. 
  • If the conditions in your region do not permit the use of herbicides, you can consider the following:
    • Though not the most efficient method, digging out the entire plant is an option to get rid of gunnera. 
    • Removing seeds heads, leaving them in a pile and covering them up to rot.

Is gunnera plant invasive?

We have already established that gunnera plants are invasive and spread vigorously through their root system, however, they also spread through seed dispersion majorly carried out by birds, insects, and running water. 

A single gunnera plant can produce up to 250,00 seeds in one growing season and though not all seeds will be dispersed or will eventually germinate, you can have an idea of how quickly they can spread and form new plants and understand why gunnera is considered as an invasive plant threatening the native species in UK and England as a whole.

In some parts of the UK, the main contributors to the extensive spread of gunnera plants are gardeners that do not understand the invasive nature of the gunnera plant and discard gunnera roots carelessly or building contractors that unknowingly transport the seeds with soil and other building materials. 

How deep are Gunnera’s roots?

Gunnera plants thrive best when planted around water because they need moist and temperate regions to survive. In a situation where a gunnera plant is grown in drier soil conditions, the roots are capable of penetrating the soil up to 1 metre to reach the moisture that they need.

Should Gunnera flowers be removed?

Gunnera is a vigorously growing, non-native plant that is considered highly invasive because of how quickly it spreads outside of its planting location. Because of its invasive nature, a ban has been placed on it in several parts of Europe including the UK. 

Gunnera tinctoria or Giant Rhubarb plant often spreads through their root system or underground rhizome and new, healthy plants can begin growing just from fragments of broken roots. Unsurprisingly, gunnera can often start growing from seeds produced from flower heads after blooming. These seeds are formed in summer around June and ripen between July and October before falling off to the ground where they can germinate and begin growing as new plants.

Based on the information on how gunnera spreads, should gunnera flowers be removed?

To curb the uncontrolled spread of gunnera, experts have advised that the flowers should be removed every summer before they develop seed. To cut the flower heads off without hurting your plant, cut them close to the base with a pruning saw or a sharp gardening knife between July and August.

Cutting off the flower heads is not enough because, without proper disposal, they will be dispersed and still grow in other locations. You can properly dispose of flower heads or seed heads at recycling depots or organic wheelie bins around the city. 

Alternatively, after cutting off the flower heads, you can leave them in a covered pile on the floor and they will rot quickly since they are no longer attached to the parent plant.

Covering the pile will reduce airflow to the seeds and flower heads, catalyze the rotting process, and hide the seeds from birds that are likely to transport them. 

Though removing the flower heads will not eliminate the parent plant, it reduces the prospects of the unwanted spread of gunnera. 

If you would like to read more about Gunnera:



Last Modified: May 19, 2022