Most gardeners are familiar with invasive weeds, such as dandelions and nettles, which we do our best to control in the garden. But some ornamental plants have the potential to grow out of control, too, which can out-compete plants growing nearby.
You may be familiar with the worst offenders, including Japanese knotweed, Himalayan balsam and Rhododendron ponticum. These are so invasive that there there are now laws in place to limit their spread into the wild, where they can damage local ecosystems. Some of these plants, such as Japanese knotweed, are so rampant that, if you find them growing in your garden, you may have difficulty getting a mortgage (or remortgaging your home), and you will be prosecuted if you allow them to spread into a neighbour’s garden.
However, there are other invasive plants that you might not be aware of. These are readily available in garden centres and are grown as ornamental plants. While not considered so invasive that we recommend you don’t grow them, you may want to think twice about growing them if you have a small garden, or if you’re after a low-maintenance planting scheme.
As with garden weeds, control of these plants includes mechanical removal such as digging the plants out by hand, and use of a systemic weedkiller. Whichever option you choose, you may find that it takes several years to fully remove the invasive plants. The key is to be vigilant and patient.
Browse our list of invasive garden plants, below.
Widely available from garden centres, Japanese anemones (Anemone hupehensis, Anemone hupehensis var. japonica and Anemone × hybrida) are delightful herbaceous plants, bearing pink or white open flowers with bright yellow centres. Flowering late in the season, they provide a good source of pollen and nectar for late-summer insects, when little else is in bloom. However, they can be invasive. Spreading by underground runners, they can quickly become out of control, and are very difficult to eradicate. They tend to be most invasive in loose, sandy soils, so consider growing them in a pot if you’re worried.
Bear’s breeches, Acanthus, (such as Acanthus mollis or Acanthus mollis ‘Whitewater’) is a large, structural plant, bearing enormous, glossy lobed leaves and tall flower spikes of white flowers surrounded by a purple bract. It’s perfect for growing at the back of a mixed herbaceous border and its blooms may be used in cut flower arrangements. While it doesn’t spread, it does grow into a large clump, which is relatively trouble-free unless you want to move it. However, if you do decide to move it, you may find you’re unable to eradicate it from its original spot – its roots are so deep that it’s hard to remove them all when you dig the plant out of the ground. These then quickly grow into new plants, which can prove impossible to get rid of.
There are two types of bamboo: clump forming and running. Clump-forming bamboos include Bambusa, Fargesia and Thamnocalamus. These usually cause no problems in the garden and don’t spread. However running bamboos, which spread by long underground runners, or rhizomes, can be incredibly invasive if not managed properly. These include Phyllostachys (pictured), Pleioblastus and Pseudosasa. If not contained, these bamboos can quickly spread, out-competing other plants. Digging them out can be problematic and you may need to seek professional help.
While our native bluebell, Hyacinthoides non-scripta, is welcome in gardens, the larger Spanish species, Hyacinthoides hispanica, can cause problems. Stronger growing than native bluebells, it seeds more freely, meaning it can quickly invade your garden. What’s more, the Spanish species can hybridise with the native bluebell. This hybrid form can escape gardens and – in rural areas – has the potential to out-compete and even eradicate our native species.
Spanish bluebells bulbs are larger than those of the native species. It’s possible to dig the bulbs out of the soil but it’s likely that it will take a couple of years to remove them completely. Their spreading nature means you may have to dig out other plants to get to the bulbs.
There are several species of passion flower, but the most commonly grown species, Passiflora caerulea, is extremely vigorous and can become invasive. It spreads by long runners and throws up shoots, or suckers, several metres from the original plant.
Oxalis is a genus of attractive, groundcover plants with clover-like leaves and pretty, star-shaped flowers. However some species can be invasive. Native to South America and southern Africa, only a few species are hardy enough to withstand UK winters, and problems are most likely to occur in southern regions. The most problematic species are Oxalis corniculata, Oxalis debilis and Oxalis latifolia. They spread by bulbils, which can remain dormant in the soil for several years, or seed, which is fired from exploding seedpods. Some species, such as Oxalis latifolia, spread by both seed and bulbils.
Bachelor’s buttons, Kerria japonica ‘Pleniflora’, is a delightful spring-flowering shrub, bearing fully double, bright yellow blooms when little else is in flower. Tolerant of sun and shade it can be grown almost anywhere. However it spreads by suckering rhizomes and needs careful management to stop it from growing out of control.
Yellow loosestrife, Lysmachia punctata, is a fantastic perennial, bearing tall spires of long-lasting yellow blooms, which are extremely attractive to pollinators. It’s perfect for a space that needs filling quickly, and is not too much of a problem if grown in poor soil in shade. However, given a rich loamy soil and full sun, it’s hard to control, spreading both by underground runners and seed. Divide large clumps every three years to control the spread, and take care to remove suckers when you see them.
Houttuynia cordata is a low-growing shrub, with dark leaves and simple, white flowers with prominent centres. The cultivar ‘Chameleon‘ has variegated foliage in green, red and yellow. Ideal for growing around the pond edge or in a bog garden, it has a tendency to spread, both by runners and seed. You can restrict its growth by growing in drier soils or a pot.
Snowberry, Symphoricarpos, is a suckering shrub, bearing pure white berries from autumn into winter. It can be grown virtually anywhere, and is tolerant of poor soil. Grow it as groundcover, beneath trees, or even as an informal hedge. However, due to its suckering nature it does have a tendency to spread and can be hard to manage. Its runners are long and suckers can turn up far from the original plant, and can be difficult to eradicate from the lawn. You may find it takes several years to fully eradicate snowberry.