Garden thugs: potential nuisance plants

Most gardeners are aware of the problems caused by weeds, but there are garden plants - readily available to buy - that have the potential to become a nuisance. Gardeners may buy these 'thug' plants unaware that, once established and given the right growing conditions, they can run amok.

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Japanese anemones can become invasive as times. Credit: RHS/John Trenholm.
Japanese anemones can become invasive as times. Credit: RHS/John Trenholm.

Quick facts

Five 'thug' plants commonly available:
  • Leyland cypress
  • Japanese anemones
  • Mind-your-own-business
  • Blackberries
  • Mint

What are garden 'thug' plants?

Garden thugs are those plants that can quickly get out of hand in the garden, even though they are not regarded as weeds and are commonly sold in garden centres.

Think carefully about introducing these plants to your garden, and be prepared to carry out judicious pruning and digging or

thinning out as required.

Examples of such plants include:

Trees and shrubs


Bamboos, sedges, reeds and grasses

Herbaceous perennials

Crevice plants

Edible crops

Ground cover plants

Bulbous plants

Pond plants

There are a number of aquatic plants that can easily get out of hand in a garden pond and are considered true weeds. Ideally these should never be introduced to the pond, though they sometimes come unwittingly with other pond plants.

The problems

Trees like the Leyland cypress and climbers such as Russian vine can grow so quickly that they are soon much too big for the garden.

Trees such as poplar and sumach have a tendency to sucker, sending up shoots all over the garden and even in neighbours’ properties.

Many ground cover shrubs like the snowberry or Hypericum calycinum spread via underground stems (rhizomes), sending up new plants and gradually taking over the border. Some bamboos also behave in this way, becoming a constant source of regret for the gardener.

Potentially invasive herbaceous plants and grasses, such as Japanese anemones and Phalaris arundinacea, form ever-enlarging clumps that require frequent division. Others, such as golden rod or weeping sedge also spread by seed, with seedlings popping-up in unexpected places where they are not wanted.

Bulbous plants such as Oxalis can produce tiny new bulbs, or offsets, which are scattered every time a clump is dug up, spreading the problem rather than controlling it.


First, consider whether this can be done using non-chemical means such as digging out or suppressing with mulch. Where these methods are not feasible, chemical controls may need to be used.

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Cultural control

Hoe off or hand weed seedlings when small. Better still, try to remove dead flower heads regularly to prevent seed dispersal. Other garden plants that can become prolific self-seeders include Anemanthele lessoniana, camassia, chivesfennel (Foeniculum vulgare), Nectaroscordum siculum, sisyrinchium and Verbena bonariensis.

Dig or fork out established unwanted plants. Suppression under a layer of cardboard topped with a 10cm (4in) layer of organic matter is an alternative but could take several growing seasons to be effective. 

Beware putting invasive plants and their seedheads on the compost heap, as this is unlikely to reach a high enough temperature to kill off seeds, tough roots or underground stems. Instead, place them in the municipal green waste, as this is composted on an industrial scale, where tough weeds should be killed off. Burning may also be appropriate, but check your local Council guidelines.

Weedkiller control

The RHS does not support the use of weedkillers and recommends that alternative control methods are used. However, we do note that when gardeners struggle to control plants with cultural methods, regulated weedkillers/pesticides for home gardeners are available for use legally. Garden centres and large retailers selling weedkillers have trained staff who can advise on suitable products for your needs.

Weeds: non-chemical control

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The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.