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

Pulling out some of the seedlings, usually along a row, so the remaining seedlings are spaced further apart. It reduces overcrowded, which can hinder their growth.

Examples of such plants include:

Trees and shrubs

• Cherry laurel (Prunus laurocerasus)
• False acacia (Robinia pseudoacacia)
• Kerria japonica
• Leyland cypress (× Cuprocyparis leylandii)
• Poplars (Populus spp.)
• Sorbaria
• Sumach (Rhus typhina)
• Symphoricarpos × doorenbosii

Climbers

• Passion flower (Passiflora caerulea)
• Russian vine (Fallopia baldschuanica)

Bamboos, sedges, reeds and grasses

• Sasa palmata (see our bamboo profile for a fuller list of invasive bamboos)
• Phalaris arundinacea
• Phragmites australis
• Weeping sedge (Carex pendula)

Herbaceous perennials

• Bear's breeches (Acanthus)
• Chinese lantern (Physalis alkekengi)
• Golden rod (Solidago canadensis)
• Houttuynia cordata ‘Chameleon’
• Japanese anemone (Anemone × hybrida cultivars)
• Macleaya spp.
• Soapwort (Saponaria officinalis)
• Yellow loosestrife (Lysimachia punctata) 

Crevice plants

• Mind-your-own-business (Soleirolia soleirolii)

Edible crops

• Blackberries
• Raspberries
• Horseradish
• Jerusalem artichoke
• Mint

Ground cover plants

• Comfrey (Symphytum spp.)
• Creeping Jenny (Lysimachia nummularia)
• Euphorbia cyparissias
• Hypericum calycinum
• Leptinella squalida
• Periwinkle (Vinca major and V. minor)
• Pratia pedunculata
• Rubus biflorus
• Snowberry (Symphoricarpos albus)
• Yellow archangel (Lamium galeobdolon) 

Bulbous plants

• Allium paradoxum and A. triquetrum
• Arum italicum
• Lesser celandine (Ficaria verna subsp verna (syn Ranunculus ficaria)) cultivars
• Nothoscordum borbonicum
• Oxalis culitvars

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.

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, chives, fennel (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