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.

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

Climbers

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.

Control

Non-chemical 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, chives, fennel (Foeniculum vulgare), Nectaroscordum siculum, sisyrinchium and Verbena bonariensis.

Digging out unwanted plants may work for a while, but is only likely to be a temporary solution. Suppression under black plastic or weed membranes is an alternative but again 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 (it is all right if they have already been killed off with a weedkiller). 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.

Chemical control

For herbaceous weeds, try a programme of spraying using a systemic herbicide containing glyphosate – Roundup and Tumbleweed are common brand names of such products. For woodier plants, choose triclopyr (SBK Brushwood Killer) or glyphosate formulated for stump killing (e.g. Deep Root Ultra Tree Stump & Weedkiller).

Download

Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 1a and 4)

Links

Chemicals: using spot and broad-scale weedkillers
Chemicals: using a sprayer
Chemicals: using safely and effectively
Weeds: non-chemical control

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