Some plants are model tenants at first. They fill a gap fast, dress up a bare fence or bring colour to a dull corner, but then they keep growing. Roots spread, seedlings appear between paving slabs and climbers make their way over into next door.
Fast growth isn't necessarily a reason to rule out a plant, but it is worth considering how much space it will need once established and whether it suits your garden.
Ahead, we spotlight five popular plants that need the right space and a little upkeep to stop them taking over.
1. Mint
Mint may look harmless in the pot you bought it in, but plant it in open soil or a raised bed and it can spread well beyond its original spot. Its roots send out runners, allowing new growth to appear some distance from the plant.
Lindsey Chastain, experienced gardener and homesteader, warns: “Mint can spread everywhere very quickly. It won't stop spreading until it runs out of soil.”
Keeping it contained from the outset is the easiest option. Christine Saah Nazer, a container and small-space gardening expert and founder of The Blooming Deck, says: “In a small garden, I think it's much easier to keep mint in a pot where you can control the roots. That's what I do and advise.”
How to keep it in check: grow mint in a container, or sink a bottomless pot into a border if you want it in the ground. Check occasionally for roots escaping over the rim.
2. Wisteria
Wisteria is prized for its cascading spring blooms, but it becomes large and woody with age. Without regular pruning and sturdy support, it can outgrow its space, strain trellises and fences, and crowd nearby plants.
Christine says wisteria is one climber that can catch gardeners out. “Wisteria is another one that can surprise people. It's beautiful, but it can become very large and woody and needs regular pruning to keep it from taking over a trellis, fence or nearby plants.”
She advises particular caution in smaller gardens: “I'd be especially cautious with it in a small space. In fact, I'd only plant this on a large trellis.”
The RHS recommends pruning wisteria twice a year. Cut back the whippy green side shoots in July or August, then shorten them again in January or February to two or three buds. This keeps the plant within bounds while encouraging flowering the following year.
How to keep it in check: plant wisteria only where there is room for a strong, permanent support and be prepared to prune it in summer and winter.
3. Buddleja (Butterfly Bush)
Buddleja produces dense, nectar-rich flower spikes that are popular with butterflies and other pollinators, but some varieties can become much larger than expected. Left unchecked, they can grow several metres tall and wide, while established plants can produce large numbers of light, winged seeds that are carried on the wind.
Lucie Bradley, gardening expert at Easy Garden Irrigation, says: “Keeping buddleja in check requires a three-pronged approach of hard pruning, effective deadheading and targeted root removal.”
For standard Buddleja davidii varieties, Lucie advises cutting the main stems hard back in spring to between 30 to 60cm above ground to prevent the plant becoming an “unruly tree.”
To reduce unwanted seedlings, she recommends removing faded flower spikes from midsummer onwards: “Once a flower head is over 25% faded, you can use your pruners to cut back the stem to about 1cm from a healthy pair of leaves.”
If space is limited, dwarf varieties such as 'Butterfly Candy Little Purple' are a better option. This variety reaches a spread of around 80cm.
How to keep it in check: cut it back hard in spring and remove fading flower spikes through summer before they set seed.
4. Bamboo
According to the RHS, Bamboo has become a popular choice for garden screening in the UK, thanks to its fast growth and evergreen foliage, but some types are much easier to contain than others. The RHS divides bamboo into two main groups: clump-formers and runners. Running types spread more readily, while clump-forming varieties generally stay in a tighter group.
Running bamboo spreads through underground stems, producing new shoots beyond the original planting area. The RHS recommends using root barriers, planting bamboo in containers or choosing clump-forming types such as Fargesia or Chusquea.
Christine also advises caution with running types in smaller gardens. “I’ve seen it take over spaces where I live and it’s costly and a hassle to remove,” she says. “It can spread underground and become very difficult to contain once it gets established.”
How to keep it in check: avoid planting running bamboo directly in the ground unless you have a proper root barrier and are prepared to check for shoots beyond the planting area.
5. Virginia Creeper
Virginia creeper can cover bare walls and fences with attractive autumn colour, but it can grow rapidly and very tall if left unpruned, creating dense growth that can shade nearby plants.
Pieces of growth can root if they are left in contact with the soil, so Lucie warns that “prunings should not be left on the ground where they can take root.” Cut the vine back in early winter after the leaves fall, particularly where it is approaching roofs, gutters or windows.
Take care when removing stems from painted surfaces. Its tendrils form pads with “a sticky resin that anchors the plant in place,” Lucie says, which can strip paint or leave permanent marks.
According to Lucie, Virginia creeper is listed on Schedule 9 of the Wildlife and Countryside Act 1981 in England and Wales. It can still be grown in gardens, but must not be planted or allowed to spread into the wild, and keep it within your own boundaries.
For small gardens, Lucie advises avoiding it altogether: “Ideally you should only grow it where you have plenty of space for it to spread, either as a fast-spreading ground cover or against a large, sturdy wall or fence.”
How to keep it in check: give it plenty of space, prune it away from roofs, gutters and windows, and make sure it does not spread into the wild or onto a neighbouring property.
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