Invasive Plants, Continued

Last year, we published a blog post about invasive plants in the UK, but it focussed on plants that grow in the wild that may occasionally encroach on our gardens, and it was like we’d opened the floodgates! There were no tales of mass intrusions from these particular plants, fortunately, but what we did hear were accounts of unwitting purchases of garden plants that had caused similar issues. We promised to cover some of these plants in another blog post, and here it is:

The fact that these plants are readily available in garden centres (though not necessarily here), suggests they’re not as big a problem as those that affect the landscape outside of our boundaries, but given our gardens are noticeably smaller than the countryside surrounding them, the damage they can cause cannot be underestimated, especially as it often comes with a sizeable price tag and can take years to completely eradicate the offenders.

Our previous blog post covered the five main culprits – all non-native plants – and it was easy to choose them, but when it comes to garden plants, there are simply too many to cover in a few hundred words! We may need to address this by revisiting the subject once again, listing all the invasive plants we can find, along with procedures for dealing with them, so watch this post…

We’ve chosen ten from the extensive list, but this is not to suggest they’re the worst contenders; they are, however, some of the most common:

Allium
There are many, many varieties of Allium, and in general the ornamental ones will cause no problems; the wild varieties, however – Allium paradoxum (few-flowered garlic/leek), Allium triquetrum (three-cornered leek), Allium ursinum (wild garlic), Allium vineale (wild onion) – are prone to spreading prolifically, and can become difficult to eradicate completely. Native to Europe, Asia and North Africa, these plants were all introduced to the UK in the 18th century and some of them can also be found growing in swathes in the wild, particularly in woodland. Their scent is unmistakable: onion/garlic! Whilst every part of these plants is edible, it would be wise to do some research before eating them to ensure you’re not picking something similar but toxic. All plants except Allium vineale have white flowers; vineale has dark red/purple flowers that are hairy. Ridding yourself of them can be quite a task! Digging them up will alleviate some of the problem, but there’s a chance small bulbs will be left behind, and when disposing of them, care is needed to prevent any bulbs escaping and taking up residence in the wild, something you could be prosecuted for. You can cover the plants with a weed-control membrane, topped-up with mulch, but you will need to keep adding mulch and it could take a number of years to destroy all plants; chemical control – never the preferred method – could be the only option but to only be used with great caution.

      

Bamboo
Clump-forming bamboos don’t usually pose a threat, but running bamboos send out rhizomes underground that spread in all directions, and it seems nothing can stop their growth. Stories of bamboo growing up through floorboards are not as uncommon as one would like to think, so if bamboo grows anywhere near your home, the potential for damage is very real. Your neighbours may not be aware of the difficulties bamboo causes, so it would be sensible to alert them to it and ask they do all they can to prevent it invading your own property; if they fail to act and damage is caused, you could make a legal claim against them; not ideal for relations, but consider the cost of removal, repairs and, when appropriate, the effect on the sale of your property. Bearing in mind that the rhizomes can spread around 4.5m in a year, the problem can quickly get out of control, and enlisting the help of a professional may be the only way to ensure the plant is removed completely. Digging it up will work, but that could mean disturbing patios or decking, and you will need to ensure all rhizomes are removed; any left behind will continue to grow and shoot. Again, weed-control membranes – along with bamboo barriers – can help if some have been missed, but only if there are very few. Chemical control is not as effective as digging the plants and roots up, so if you choose that route, be extra vigilant for the plant’s return; professional help may be the best option.

      

Bramble
Whilst most would associate bramble with country walks and picking wild blackberries, raspberries – less common in the wild – are also classed as bramble, and both can cause immense irritation in the garden. Aside from the thorny aspect to the plants, their ability to spread is admirable, although extremely frustrating. If you grow either blackberries or raspberries voluntarily, each cane can easily multiply tenfold each year, spreading under the ground in all directions, so be sure to restrict their growth if you want to prevent a coup; those invading from the wild will be unsupported, and as well as runners spreading underground, the canes will bend, and wherever they come into contact with the ground, the stem will take root. Removing them is a precarious task, given the thorny nature of the stems, and if canes are snapped off, they will simply regrow. Dealing with bramble in your own garden is your choice, but when if it encroaches from neighbouring land, whatever you remove will need to be offered back to the owner.

              

Cherry Laurel
Often grown as hedging, Cherry Laurel is tolerant of just about everything! It’s evergreen, with shiny leaves, resistant to drought, shade and mild frosts, and it grows quickly, competing very successfully with other, more sensitive plants and shrubs, muscling in and taking over; it’s seeds are dispersed by birds eating the berries, so particular care needs to be taken when planting near woodland. Although birds may well enjoy the berries, all parts of the plant are toxic to humans and pets; it does, however, make a good hedge, so remains a popular choice. Pruning can keep it in check, but due to its toxic nature, gloves are advisable. If you want to remove it completely, the plants should be fed into a chipper rather than burned to avoid releasing the toxins.

      

Japanese Anemone
Tall, striking plants, Japanese Anemones offer pink or white flowers with vivid yellow centres, and as late bloomers, they provide colour when many other plants have finished flowering. Runners spread underground – particularly in lighter soils – allowing the plant to invade all parts of the garden, often overwhelming established plants. The runners make them more difficult to eradicate completely, but careful digging – the rhizomes are quite thin and easy to miss – will do the job. Dividing the clumps regularly will help to keep them under control if you want to retain some plants, but you can prevent the spread completely by planting in pots instead of directly in the soil.

      

Mind-your-own-business
This is an evergreen, ground-cover plant, seemingly discreet because of its tiny leaves and even tinier flowers, but the pale green or pink stems creep across the surface of the soil, rooting as they go along. Although it prefers damp, shady areas, it’s not too fussy and can be found in most places, often in cracks in paths and walls, creating a lush green carpet that can provide refuge for many small insects. Removing it can be tiresome as the slightest piece of stem left behind can start the whole process again; when growing in lawns, cutting the grass will send fragments of stem in all directions, creating many more pockets of the plant. That said, removing it is relatively straightforward as the roots remain close to the surface: remove gently with a trowel or hand fork – hoeing or digging could send small pieces of stem to other areas – and cover with a thick layer of mulch to block the light.

Mint
No matter how tasty it may be, mint can become a menace in the garden – most varieties – if planted directly into the soil; the alternative is to plant it in pots, but if you have a particular spot in mind in a herb garden, you can plant it in a large bottomless pot or bucket and bury that in the soil to keep the plant in check. Digging it up can remove it if its not too dense, but there is, of course, the potential for regrowth from a tiny piece of missed root, so check frequently for regrowth and deal with it swiftly. Boiling water can work, but it will kill anything else it may come into contact with, so once again, caution is necessary; smothering the plant, however, can be very effective, but it may take some time.

      

Passion Flower
The most popular species of Passion Flower, Passiflora caerulea, can become invasive if left unchecked. Once again, underground rhizomes spread out, allowing new shoots to form away from the main plant; untrained shoots – either new ones or original – will latch on to and around to anything in their path. Careful and regular pruning will keep the plant under control, but if you want to remove it completely, you will need to dig it out. New shoots will be easy to pull up, but the main plant is likely to have deep roots, and most will need to be removed to ensure it doesn’t return.

        

Periwinkle (Vinca major and V. minor)
Another resilient plant, often used for groundcover, that will still flourish in difficult areas of the garden, but Greater Periwinkle (Vinca Major) in particular can become extremely invasive. Lesser Periwinkle (Vinca Minor) spreads across the ground, its shoots rooting as they come in contact with the soil, forming a stunning carpet of purple and green; it’s ideal for filling gaps absent of other plants and will help prevent weeds. Greater Periwinkle creeps along the ground in much the same way, but it also produces long shoots that arch and take root, and if that happens to be amongst other plants, removing it can become problematic. Planting it alone in a more inhospitable part of the garden would for better observation and control methods, should it get out of hand. Regular pruning will prevent an invasion, but be sure to dispose if in garden waste bags/bins, rather than composting, as the plant could potentially take root there.

    

Yellow Loosestrife
A tall, striking perennial, Yellow Loosestrife, produces yellow flowers that are popular with bees and other pollinators. As it spreads with underground rhizomes and via seeds, so it will fill a gap very quickly, often to the detriment of other plants. Poor soil and shade will slow it’s growth, so if you have a suitable spot to fill, it’ll do you proud; in full sun and rich soil, and can quickly take over, but dividing clumps will help to keep it under control.

This list is just a snapshot of invasive plants, and, indeed, the issues caused by them. It’s a subject we have previously covered and one we may well address again in the future. If you have any concerns about what to plant in your own garden, speak to one of our experts; not only will it give you peace of mind, it could save you a lot of time and money.

Some photos curtesy of Pixabay