In general, people consider invasive plants that do not grow naturally in their area. In other words, invasive plants are non-native species that show up outside their natural range habitat and that threaten the local flora and fauna.
This phenomenon is possible due to the direct or indirect introduction of these plants by humans over time. When these plants settle in their new home successfully, whether it is in a natural or controlled environment, they become naturalized.
These plants may end up becoming invasive for different reasons. For example, they have a relatively rapid rate of spread via seeds or vigorous roots. In some regions, it can also be a lack of control mechanisms, such as herbivores or human actions.
In other cases, invasive plants become an issue because they do not encounter real competition with other species, so they manage to absorb more space and resources than their native neighbors.
Although some of these naturalized species do not typically present a common problem for the region they now grow in, there are others that can actually become dangerous (and even annoying). Non-native invasive species tend to spread as they like, competing with native species for space and resources and, very often, winning the battle.
This habit can threaten the local ecosystems, the surroundings of the invasive plants, and even the native flora and fauna. To help you avoid growing these dangerous and fast-spreading plants in your garden, we’ve created a list with a few notable examples.
What Are The Most Common Invasive Plants in the UK?
Himalayan Balsam (Impatiens glandulifera)
Himalayan balsam is a pretty large-growing annual species that originate from the Himalayas. In Europe, this plant was added to the list of Invasive Alien Species in 2017. Himalayan balsam has become naturalized and is quite a widespread plant that thrives on riverbanks.
- People cultivate the Himalayan balsam for its attractive purple flowers that resemble the shape of a policeman’s helmet.
- However, after its blooming period has come to an end, this plant produces seed pods that explode easily when disturbed.
- This is why the plant tends to become highly invasive, as it can scatter the seeds at a distance of up to 23 feet (7 m).
Controlling the spread of Himalayan balsam can be pretty difficult and can make you spend too much time on its caring routine. But if you like the overall look of this plant, the good news is that you can find plenty of non-invasive species that look very similar to it. Some of these are Joe Pye, Foxglove Beardtongue, Pink monkshood, Dictamnus Gas plant, or Meadowsweet.
Japanese Knotweed (Reynoutria Japonica)
Japanese knotweed is a species that will not hesitate to spread rapidly through its vigorous underground rhizomes. This Asia-native weed is, without a doubt, an eye-appealing ornamental. It has managed to successfully settle in many habitats and it appears listed as one of the world’s worst invasive species.
- This plant usually dies back to the ground level during the winter months. But when it comes back, in early summer, its bamboo-like stems will emerge even at a distance of 7 feet (2.1 m) from the main plant.
- This particular habit of the Japanese knotweed makes it a difficult plant to handle and care for.
- With its fast and uncontrollable spread, it can even take the space of other plants that grow around it, affecting their overall health with time.
- Likewise, its invasive and strong root system can damage roads, architectural sites, buildings, and other structures.
There are various plants, woody shrubs, and trees that you can use to replace the Japanese knotweed, such as Bamboo, Guelder rose, Lilac, Houttuynia, Persicaria campanulata, Himalayan honeysuckle, Broad leafed dock, Hawthorn, and Red bistort. These plants are rarely dangerous and you can control their spread much easier.
Giant Hogweed (Fallopia Sachaliensis)
If you want to find out how terrible having Giant hogweed in your garden can be, just know that it can take at least ten years to eradicate this plant. Giant hogweed dies after it produces seeds, leaving dried stems behind with seed heads standing.
- On average, just one Giant hogweed plant can produce 20000 seeds but, depending on the specimen, it can also reach 50000 seeds.
- These seeds typically spread over short distances through the wind. Still, they can travel much longer distances with the help of animals, water, and people.
A few non-invasive replacements for the Giant hogweed would be Blue elderberry, Shield leaf rodgersia, Ligularia, Rodgersia, Wild parsnip, or Angelica.
Green Alkanet (Pentaglottis Sempervirens)
There is much to say about Green alkanet, as this plant is much more than it meets the eye. Besides its ordinary ornamental purposes and bad reputation as an invasive plant, this buddy produces edible flowers.
- It is a popular species for pollinators, and also a great food source for the larvae of some moths.
- Moreover, Green alkanet will basically grow where little else will, so you can find a spot for it with minimal effort.
- On the other hand, that spot will not remain the same size with time. Like many other invasive species, Green alkanet will use its deep, brittle tap roots to spread wherever it wants to.
- This habit makes it a bit tricky to control its growth or even eradicate it completely.
If the vibrant blue blossoms of Green alkanet are the ones that piqued your interest, we have great news! You can replace this invasive species with other interesting ones that look very much like our complicated friend right here. These include the well-known Forget-me-not and Brunnera.
Rhododendron (Rhododendron Ponticum)
In western Europe, Rhododendron ponticum and its varieties enjoy lots of popularity as ornamental plants. And we surely can see why! These flowering plants exhibit stunning curly, violet-purple blooms that often come along with small greenish-yellow streaks or spots for the perfect look.
- Yet, although Rhododendron ponticum is safe to grow in some areas and its spread can be controlled, it tends to be more invasive in the UK.
- This plant is a mix of troublesome, multiplying like crazy through both its roots and seeds.
- It crowds out the native flora and some studies have also shown that its flower nectar can be pretty toxic to European honeybees and other native bee species.
Luckily, you can find lots of similar non-dangerous alternatives for the showy display of Rhododendron ponticum. Look for plants like Rhododendron ‘Cunningham’s White’, Holly, Crab apple, Hazel, Juniper, Wild cherry, or Hawthorn.
Swamp Stonecrop (Crassula Helmsii)
As always, we couldn’t possibly leave our beloved succulents behind, especially when there are so many gardeners out there who grow them outdoors. Also known as New Zealand Pygmyweed, the Swamp stonecrop is native to Australia and New Zealand, but it has been naturalized around the world. In the UK, this succulent is among the five invasive aquatic species which have been banned from sale since 2014.
- Once the Swamp stonecrop establishes in an environment, it will grow vigorously and its spread can become out of control.
- This succulent usually thrives on the muddy margins of ponds. It forms fully-covered carpets that can be totally or semi-submerged in deep water.
In case you have dreamed about a complete succulent collection comprising the Swamp stonecrop, it might be a bit challenging to do it. But do not worry! You can always go on and find many other non-invasive species of succulents that are also easy-going in the long term!
American Skunk Cabbage (Lysichiton Americanus)
The American skunk cabbage has settled nicely in UK’s wet woodlands, where it tends to overcrowd the native plant species. Prized for its absolutely fabulous flowers, this plant also has a very distinctive feature.
Wherever it grows, the American skunk cabbage makes its presence known by emitting a strong skunk-resembling perfume, hence its common name.
Other than looks, people love the American skunk cabbage for its ability to behave nicely in wet areas.
If you do not mind the extra work that comes packed with having this plant in your garden, you can be adventurous and do it!
If not, however, you can opt for alternative species that are more friendly and independent, such as Yellow flag iris or Marsh marigold.
Water Primrose (Ludwigia Grandiflora)
Commonly known as Floating primrose-willow or Water Primrose, these plants thrive in riparian and wet habitats with slow-moving or still water. Ludwigia plants are tolerant of water level fluctuations and they can spread quickly in places such as lake margins, ponds, ditches, bogs, and all types of wetlands.
- When released in the wild, water primroses can cause all sorts of problems. These invasive plants can wreak havoc on native habitats.
- Their fast-spreading habit can quickly outgrow and out-compete native species. Another frequent problem that these plants can cause is clogging waterways and even contributing to flooding.
- Ludwigia plants can easily spread through stem fragments and it can also spread through seeds, so removing it is a difficult process.
- These plants are currently banned for sale in the UK and they are also on the Rapid Response list in the UK, which means that when detected, they are targeted for immediate eradication.
Although Ludwigia water primroses are dangerous, they are quite attractive, so you might want to find a similar plant to grow in your garden. If you want to avoid Ludwigia plants but wish to fill your garden with yellow aquatic blooms opt for Nymphaea, Mimulus, Nuphar lutea, Marsh Marigold, Water Canna, and Orontium aquaticum.
How to Control The Spread of Invasive Plants?
When we are talking about controlling the spread of invasive plants, there are a few essential steps that you should remember. At first, you will have to make sure that your garden is tidy and that you remove the weeds regularly.
- You should not allow weeds to grow and spread as they wish because they can become very difficult to get rid of when left to their own devices. Likewise, you must choose a way to get rid of weeds that will not put human health or the environment in danger. Read our guide on how to get rid of weeds naturally to learn more about this process.
- A great way to control the spread of edgy weeds is by either pruning them regularly or by introducing natural enemies for these weeds. For species that spread through seeds, it is best to cut them back to prevent the seeds from dispersing wherever they wish. The perfect time to do this is right when the flowers begin to fade. This will not allow the weeds to bear fruits, which are usually the source of seed production.
- If you are in a difficult situation and you can’t remove an invasive plant, you might need something that shows results faster. In this situation, it might be best to use a weedkiller product that you can find commercially in markets or nurseries.
- Once you have a suitable weedkiller for your problematic weed, all you have to do is spray it regularly until you see no sign of foliage on it. After you do this, it would be wise to dig out the plant to prevent its underground roots from spreading.
How to Dispose of Invasive Species?
In case you want to get rid of the invasive plants for good, there are several efficient ways to do it depending on the type of weed you are dealing with.
- The easiest and most upfront solution is to pull or dig out the alive, dying, or dead weeds.
- Once you do this, you can also burn on the site to make sure that nothing has been left from the plants. If you do not burn the location in which the weeds have grown, it is possible to miss some parts of their roots which can easily turn into brand new weeds.
- For aquatic species of weeds, you should first apply as much compost as you can around them. Likewise, you can bury them in trenches in your garden. When the weeds have dried out, you can burn them to prevent future unwanted growth.
- If you encounter common invasive weeds, such as the Japanese knotweed, Giant hogweed, or Himalayan balsam, things are a bit different. You must first control their spread with a weedkiller or dig them out and then burn them on the site.
- Under some regulations, these weeds are “controlled waste”, so you will have to check with your local council for the nearest site that is suitable for your issue. Keep in mind that you should not put burnt weeds in your normal household waste!
With other non-native invasive plants, you can do the same regarding the weedkiller control or simply dig the plants up from their growing medium, and then burn them on site. Another great suggested way to dispose of them would be as normal green waste through your local recycling.
How can you protect the local environment while gardening?
Looking after the environment is very important and you should be mindful of the native flora and fauna while caring for your garden. To allow future generations to enjoy a healthy environment, make sure you follow a few simple steps:
- Be familiar with the plants that grow in your garden – Knowing what you grow is an important step towards creating a healthy ecosystem in your backyard. Choosing the right plants for your garden, whether you’re growing a cottage garden, a vegetable garden, a pond garden, or a woodland garden is a great way to lend a helping hand to the native plants and animals. If you know what you grow, you are less likely to introduce or spread invasive species.
- Keep your plants in check – Whether you are growing native plants or exotic ones, make sure you do your due diligence and keep your plants in your garden. A common way in which invasive plants managed to spread is through careless gardening. So, unless you are 100% sure that a certain plant is beneficial to the local ecosystem, keep it within the limits of your property.
- Compost and discard plants with care – As mentioned above, invasive species have many different ways of spreading. Some produce seeds that will easily be carried by the wind, while others spread through underground roots. Therefore, it is very important to be extra careful when it comes to disposing of unwanted plants, including their branches, flowers, seedpods, roots, and other fragments.
Invasive plants can become a real problem when left to their own devices. As gardeners, it is our duty to protect the native flora and fauna by avoiding these dangerous species of plants.
If you come across invasive non-native plants on your property, it’s highly recommended to stop them from spreading before they spread to nearby lands and cause damage to the ecosystem.
If you do not remove invasive species from your land, you could be held responsible for the damage they cause. If you need help, you can find more information here.
If you have any suggestions of invasive plants that should be avoided in the UK, or if you’ve had an interesting experience with such plants, let us know in the comments!