Trouble in paradise: Plants to avoid in your garden this summer - which could land you fines of up to £5,000

The warmer weather is a great time to spruce up your garden, removing weeds and adding in colourful new plants to brighten things up.

However, there are a number of plants - including a few garden favourites - that environmentalists are urging green-fingered Britons to pass over when picking their garden plants this year. On top of that, there are a number that actually face legal restrictions under the the Wildlife and Countryside Act 1981, which have been classified as invasive.

These plants can cause massive harm to the British Isles’ ecosystems if they are allowed to spread unchecked, outcompeting or even directly harming native plants and wildlife. More than 50 plants - some of which share the same common name - are listed under the act, and face differing levels of controls. While it is usually not an offence to have these plants growing in your garden and there is no legal requirement to control them, either planting them in the wild or allowing them to spread is an offence. There are also legal restrictions on selling plants classified as invasive.

Here are some of the most common plants covered by the law, and what threat they pose outside the garden - as well as what kind of penalties you could face for letting them spread:

Japanese knotweed

Originally brought to the UK as an ornamental plant, Japanese knotweed has attractive white flowers - and was historically used sometimes in mixed hedges. It’s popular with bees and wild food foragers, but it’s a big problem in Britain.

According to the Royal Horticultural Society (RHS), its bamboo-like stems grows rapidly in the springtime and can quickly reach more than seven feet tall. This chokes out other plant life, and its aggressive growth can even damage structures or buildings. If you are planning to sell your house, you’re also legally required to check for and report knotweed on the property for this reason - potentially devaluing your property.

Unfortunately, controlling knotweed usually requires a professional, as it is hard to remove and illegal to throw it out with your regular garden waste. If contaminated soil or plant material leads to the spread of Japanese knotweed in the wild, UK residents could face a prison term of up to two years, the home insurance team at Compare the Market says. Residents can also face fines of up to £5,000 if they allow it to spread into natural areas.

Giant hogweed

Another once-ornamental escapee, anyone who knows about giant hogweed likely doesn’t want it in their garden to begin with, but this particularly pernicious weed has its ways of getting around. The sap of this cow parsley cousin can cause severe skin burns if you get it on you as it reacts with sunlight, causing blistering and sometimes lifelong scars.

You don’t legally have to control it in your garden. But similarly to knotweed, allowing it to spread outside your property - even to neighbouring ones - is illegal, and according to CEL Solicitors, could be cause for your neighbours to make a legal claim against you.

Rhododendrons

Surely we couldn’t mean the beautiful, flowering trees popular at botanical gardens and parks across the UK? But we do. Rhododendrons - including the popular azaleas - spread via seed incredibly quickly, and are notoriously expensive and difficult to remove.

The Woodland Trust says the plant is capable of wiping out huge swathes of native woodlands, and is particularly dangerous to Britain’s rare temperate rainforests. Imported rhododendrons also frequently carry a deadly plant disease called Phytophthora ramorum, which can be fatal to more than 150 other plant species. In the UK, attempts to control this disease has resulted in large scale felling of larch plantations, which harms the domestic timber industry too.

While it is technically legal to buy and plant these shrubs in your garden, the Trust urges Brits to avoid them for the sake of nature. But if species listed in the Wildlife and Countryside Act - which include Rhododendron luteum (yellow azalea) and the common Rhododendron ponticum and its hybrids - you could be liable for the same hefty fines.

Himalayan balsam

One of the lesser-known plants on the list, the RHS says this flowering plant is a relative of the popular ‘Busy Lizzie’. It was also introduced as a decorative garden plant, known for its helmet-shaped pink and purple flowers and attractive seed pods.

But these seed pods explode - launching seeds outwards up to seven metres - every year, according to the Norfolk Non-Native Species Initiative. The plants form thick stands, particularly along riverbeds, blocking out other plants from growing. They’re particularly attractive to bees, but unfortunately this makes them less likely to visit and pollinate other native plants - leading to the decline of them and other wildlife in turn. When they die back in winter, they also make these riverbanks more likely to erode and collapse, which can worsen flooding issues.

Himalayan balsam is known to spread onto gardens and allotments, and sometimes the seeds are passed along to prospective gardeners by people who spot their pretty flowers. But it is once again illegal to lead it spread beyond your property - and given its explosive nature making this hard to control, it’s probably better to steer clear altogether.

New Zealand pigmyweed

This one is an aquatic plant, one of five water plants added to the ban list in 2014, so decorative pond owners should beware. Only introduced to the UK in the 1950s to help “oxygenate” ornamental ponds and aquariums, it is now effectively banned - and it is illegal to sell this plant at all.

Also known as the Australian swamp stonecrop, this plant is believed to have made it into the wild via people emptying the contents of their ponds or aquaria to clean them out. It’s possible they may still be being spread this way, as well as by boats used in different bodies of water, and possibly waterfowl. According to Great Britain’s Non-Native Species Secretariat, pigmyweed forms dense mats in waterways, actually depleting oxygen and potentially suffocating fish, frogs and insects. A few pet deaths have also been reported, where dogs have jumped onto pigmyweed thinking it to be land, and being unable to free themselves.

Like the other plants on the list, if you do find it growing in your pond or a waterway on your property and you dispose of it incorrectly or allow it to spread, you could still be liable for a hefty fine.