20 plants that should come with a health warning

A picture of a bamboo that had muscled its way through a living room wall and threatened to engulf the sofa grabbed my attention. That was just an initial flick through a copy of the recently published Invasive Bamboos by Brian Taylor, Jim Glaister and Max Wade (Packard, £35).

But bamboos are not the only garden space invaders. Many other garden plants that are widely sold can become problematic. Some are attractive plants that were originally chosen to fulfil certain roles, but were subsequently found to run amok in average garden conditions.

As a cohort of new gardeners – prompted by Covid lockdowns – takes up gardening, now is a good time to look at the garden plants that should come with a health warning. Understanding plant growth habit is key, in addition to following “right plant, right place” principles.

Common plants that should come with a health warning

Invaders we can learn to live with

Gardeners have their own tipping points when it comes to deciding when a desirable plant has become a thuggish nuisance. The RHS list, Garden Thugs: Potential Nuisance Plants includes edibles such as blackberries and raspberries – but that shouldn’t put anyone off growing them. Mint is also listed – although growing it in a pot easily contains its spreading tendencies.

Many self – seeding plants are potentially invasive, but in many cases (eg viola and erigeron), their attractiveness tilts the balance away from nuisance. Gently intervening in the seeding process prevents plants from becoming a problem – for example deadheading (cutting off faded flower heads before they set seed). And, once you have learned to recognise them, just pulling up excess seedlings.

Many gardeners are happy to tolerate all of these plants because it’s easy to remove excess seedlings:

• Alchemilla mollis

• Aquilegia

• Erigeron karvinskianus

• Euphorbia characias subsp. wulfenii

• Linaria purpurea

• Lychnis coronaria

• Muscari armeniacum

• Stipa tenuissima

• Verbena bonariensis

• Viola riviniana Purpurea Group (labradorica)

Invasive plants and the law

The Wildlife and Countryside Act 1981 lists plants that must not be planted or caused to grow in the wild. You must not import, transport, keep, breed, sell, use or exchange these plants. But, confusingly, you do not have to remove these plants or control them on your own land. It is allowing a listed plant such as Japanese knotweed to invade anyone else’s property that can lead to a community protection notice or prosecution.

The Act originally listed only Japanese knotweed (Reynoutria japonica) and giant hogweed (Heracleum mantegazzianum). Other well known baddies include Himalayan balsam and Rhododendron ponticum. The list was increased to 36 plants in April 2010, and in 2014 the top five most invasive water plants were banned from sale.

Currently, no specific legislation covers the sale, planting or spread of bamboo, or any of the plants above, into adjoining properties or the wider environment. For guidance, visit gov.uk and search “invasive plants rules”.

What about nuisance hedges?

The Anti-social Behaviour Act, 2003, covers high hedges but it does not cover shading or garden plant invasion. Where plants cause damage to neighbours’ gardens and properties, as in the case of bamboos, the Anti-social Behaviour, Crime and Policing Act, 2014, enables local authorities and police to issue community protection notices when it is shown beyond doubt that the individual in question has persistently acted in a way that has a detrimental effect on the quality of life of those around them.

That said, nature can still outsmart even the most diligent gardener. Sometimes you just have to go with the flow, provided plants are not harming your home or invading your neighbours’ property. Most gardeners have their own list of charming rogue plants that, despite some anti-social habits, they wouldn’t want to be without. Below, I’ve selected 20 real pests and ten nuisance-but-nice plants to watch out for.

Invasive plants to be aware of

Bamboo

Appeal: attractive stems, evergreen foliage, good for privacy screening.
Problems: powerful roots with the potential to damage buildings and cross garden boundaries.
Options: Spartium junceum – good stems; Leucothoe fontanesiana – an arching evergreen; Stephanandra tanakae – good foliage.

Yellow archangel (Lamium galeobdolon)

Appeal: covers ground in shade, suited to wildlife and meadow areas.
Problems: Coarse, smothering growth; grows anywhere.
Options: Plant only in wilder areas and meadows. ‘Silberteppich’ (‘Silver Carpet’) is not invasive and makes a more compact plant.

Plume poppy (Macleaya spp.)

Appeal: tall, no staking, attractive foliage nearly to ground level.
Problems: robust running roots – strong enough to span beneath a paved path in my garden.
Options: M. cordata is more compact. Plant in large containers to prevent spread.

Mind your own business (Soleirolia soleirolii)

Appeal: fast-growing, evergreen mat of bright green ground cover.
Problems: extremely rapid spread soon reaches infestation levels.
Options: in sun, try mat-forming evergreen thyme (Thymus serpyllum); in damp soil London pride (Saxifraga umbrosa) is unfussy.

Canadian golden rod (Solidago canadensis)

Appeal: prairie native, useful in meadow-style planting.
Problems: has escaped into non-cultivated land all over Europe.
Options: S. rugosa ‘Fireworks’ (AGM) – more elegant, slow spreading, hardy. S. caesia and S. ‘Queenie’ – less common, the latter is more compact.

Hypericum calycinum (Rose of Sharon)

Appeal: reliable evergreen spreader for banks and slopes, large yellow flowers for many weeks, autumn berries, attractive to wildlife.
Problems: fast spreader, self seeder.
Options: Waldsteinia ternata – mat forming, semi-evergreen, yellow flowers in spring.

Kerria japonica

Appeal: arching ornamental green stems sometimes used as a bamboo alternative, bright yellow flowers.
Problems: vigorous suckering growth quickly forms large thickets.
Options: ‘Picta’ – variegated and compact; ‘Pleniflora’ (AGM) – double flowered; Forsythia x intermedia ‘Lynwood Variety’ or ‘Week End’.

Sumach (Rhus typhina)

Appeal: excellent autumn colour, architectural shape, fine foliage.
Problems: suckering growth habit – each shoot turns into a new plant.
Options: ‘Dissecta’ – more compact, remove suckers in winter to prevent spread. Cotinus coggygria ‘Royal Purple’ and Disanthus cercidifolius – good colour, lower maintenance.

Pheasant berry (Leycesteria formosa)

Appeal: ornamental green stems sometimes used as a bamboo alternative, graceful pendulous flowers.
Problems: spreads from self-sown seeds (and also spread by birds).
Options: autumn tidying can prevent seedlings; try Fuchsia magellanica for masses of pendulous flowers.

Bear’s Breeches (Acanthus mollis)

Appeal: architectural glossy foliage, striking flower spikes, tolerant.
Problems: strong growth expands from a central clump; tiny root segments can produce new plants.
Options: cut off outer sections of clump to reduce. Spinosissimus Group; A. spinosus are less thuggish.

Passion flower (Passiflora caerulea)

Appeal: showy flowers, an exotic climber to clothe a wall or fence.
Problems: vigorous growth can swamp a garden. Will die off in cold winters but bounces back in spring.
Options: large-flowered clematis, e.g. ‘Sieboldii’ and ‘Taiga’, can be cut back to 30-45cm in spring.

Weeping sedge (Carex pendula)

Appeal: curving stems, graceful flower heads, evergreen, suited to watersides and woodland edges.
Problems: seeds freely.
Options: C. secta – evergreen, lower growing; Miscanthus ‘Abundance’ – mounds of narrow foliage with masses of flowers.

Gardener’s garters (Phalaris arundinacea var. picta)

Appeal: upright stems with showy white-striped leaves, any soil.
Problems: roots make a dense clump, hard to reduce or remove.
Options: ‘Arctic Sun’ – more compact, less inclined to spread, good variegated foliage; ‘Feesey’ (AGM) – not as invasive.

Soapwort (Saponaria officinalis)

Appeal: masses of campion-like flowers for weeks.
Problems: invasive roots, untidy.
Options: plant among shrubs able to resist encroachment. Campanula lactiflora ‘Loddon Anna’ and Phlox paniculata ‘Monica Lynden-Bell’ are both better behaved.

Japanese anemones (Anemone x hybrida cultivars)

Appeal: easy to grow, floriferous, no staking required, perennial.
Problems: invasive once established, hard to remove.
Options: A. hupehensis ‘Hadspen Abundance’ (AGM) – clumping/more gently suckering pink form; ‘Splendens’ – compact form.

Montbretia (Crocosmia x crocosmiflora)

Appeal: Many weeks of hot colour flowers, upright foliage and habit.
Problems: invasive without regular splitting and thinning – and congested plants also flower less.
Options: Cultivars such as ‘Lucifer’ (AGM) and ‘Emily Mackenzie’ are found to be less invasive.

Wood sorrel (Oxalis cultivars)

Appeal: attractive clover-like leaves, some have pretty flowers.
Problems: spreads by self-seeding and/or tiny bulbils; easily spread by digging; can stay dormant for years.
Options: O. oregano – mauve spring flowers; Epimedium x versicolor ‘Sulphureum’ – elegant woodlander.

Chinese lanterns (Physalis alkekengi AGM)

Appeal: bright orange-red lanterns, good autumn colour at border height.
Problems: roots are invasive.
Options: Grow in pots to curb spread; display cut stems in pots in ground. Or grow dwarf tomatoes, e.g. ‘Balconi Red’ or ‘Orange Beauty’ for colourful, late season fruits.

Cypress Spurge (Euphorbia cyparissias)

Appeal: attractive ground cover with feathery foliage, many weeks of lime-green flowers, unfussy.
Problems: vigorous roots make it a quick spreader and hard to remove.
Options: E. epithymoides – compact, tidy habit, bright yellow spring flowers, burnished autumn tints.

Yellow loosestrife (Lysimachia punctata)

Appeal: easy to grow, good for naturalistic planting.
Problems: invasive creeping growth.
Options: Grow in pots sunk in ground to curb spread. L. ciliata – more refined, pale yellow flowers; ‘Firecracker’ – purple-tinted leaves and pale lemon flowers.