THE DAY OF THE GARDEN TRIFFIDS
They can cause £10,000 of damage and make it impossible to sell your home
JAPANESE KNOTWEED
THIS fast-growing plant has the ability to grow four inches in a day and its roots are so destructive it can dig into home foundations.
If you have Japanese knotweed (Fallopia japonica) in the garden you must get it treated straightaway. This pernicious plant is not shy and it is easy to spot the bamboo-like knotweed as it can grow to more than 7ft.
It is recognisable by a lime green bamboo-like stem speckled red and purple.
The leaves are heart-shaped and sprout with a reddish tinge before turning lime green. It produces a cluster of cream flowers in the summer. Jo Mullet, who runs Knotweed Control Swansea, says: ‘The plant spreads through underground stems known as rhizomes – allowing it to pop up all over the garden if it is not treated.’
If you only have one or two plants you can treat them yourself. This usually involves powerful glyphosate-based weed killers such as Roundup Tree Stump & Root Killer or Bayer Garden Super Strength Weedkiller, costing about £15.
Treatment involves cutting back the plant in the summer leaving just an eight-inch hollow stem. You then drip feed the weed killer into the hollow so that it sucks up the poison and kills all growth underground.
Japanese knotweed is classed ‘controlled waste’ by the Environmental Protection Act 1990 so you cannot throw it on the compost or in a recycling bin. You must dispose of it at a licensed landfill site. Mullet says: ‘If you find a lot of knotweed, it is time to call in the professionals. This can involve deep soil excavation and return trips to ensure all the rhizomes have been removed.’
Although this can cost up to £5,000 it will be worthwhile because if the garden is overrun with knotweed a house can become unsellable – some lenders will not offer a mortgage.
The roots can damage foundations, drainage systems and walls, costing £10,000 to fix. This is rarely covered by buildings insurance.
The current epidemic is a far cry from when Japanese knotweed was introduced to Britain in 1825 as an exotic ornamental plant.
GIANT HOGWEED
THIS noxious weed (main picture) grows up to 18ft high and if touched, you can pick up a nasty burn and blisters. In rare cases it can cause blindness.
It is often mistaken for the smaller native species cow parsley and is part of the same carrot family.
Giant hogweed (Heracleum mantegazzianum) has clusters of white flowers that spread out like umbrellas the size of dinner plates and a four-inch wide hairy green stem that is spotted with purple.
If you think you have stumbled on a giant hogweed, leave well alone. The toxic sap within the leaves and stem does not just burn the skin but can make it more sensitive to sunlight. The area of the body that touches the hogweed is more likely to burn in the sun for up to ten years. If you touch it, immediately clean the affected area with soap and water. To get rid of it, dig up the plant and then put it in a plastic bag or burn. You should be fully covered and wear both gloves and safety goggles.
Hogweed originates from the Caucasus Mountains in Southern Russia and was brought over to Britain as an ornamental plant in 1893 by Victorian explorers.
HIMALAYAN BALSAM
THIS bully will take over a garden if you are not careful, causing expensive destruction of previously well-tendered flower beds.
The Himalayan balsam (Impatiens glandulifera) can grow to 10ft in height. It has attractive pink orchid-like flowers that spread out to look like a trumpet, earning its nickname ‘policeman’s helmet’. It has oval leaves with pointed teeth around the edge.
The plant is often found on riverbanks as seeds can germinate floating in water. It regrows if cut down but it is easy to pull out as it has shallow roots.
Seeds survive up to 18 months so it is important to keep an eye out for potential regrowth.
It originally came to Britain in 1839 from the Himalayan foothills of India as an exotic greenhouse plant.
WATER FERN
THIS plant goes under a variety of names including mosquito fern and fairy moss. It spreads like wildfire
across water ponds. The fern (Azolla filliculoides) is recognised from the thick floating rosettes that grow across water in a carpet that chokes out other species and waterways.
Although it is usually green it can also have red tinges and grows at an alarming rate with cover as much as doubling in size in three days.
The dense cover blocks out light and makes life difficult for airbreathing insects, preventing them from reaching the water surface.
Gardener Henry Macaulay, from Brighton in East Sussex, says the water fern can be dangerous. He says: ‘People can walk on Azolla assuming it is damp ground. This can prove particularly dangerous for those with small children.’
One of the best – and environmentally friendly – ways to control water fern is to rake or skim it off the surface of a pond or other affected water.
But there is also a beetle known as the azolla weevil (Stenopelmus rufinasus) that can eat the plant. Specialist pest controllers such as AzzollaControl – part of the not-forprofit organisation Centre for Agriculture and Biosciences International – sells groups of weevils from £100. The fern came from South America and was first recorded in Britain in 1883. It has since clogged up many canals, ponds and ditches.
COMMON RHODODENDRON
THIS large evergreen shrub is a deceptively attractive enemy, camouflaging its true thuggish nature with large violet-purple flowers and lush leaves.
Behind the friendly façade is an aggressive plant capable of squeezing the life out of anything else in the flowerbed if given half a chance. The shrub (Rhododendron ponticum) can grow to more than 16ft in height. It spreads out with a thick leafy canopy allowing no other plants to grow nearby because they are starved of sunlight. It also poisons the soil for other plants.
Where horizontal branches touch the ground they will root, continually spreading out the cover area.
Macaulay says: ‘Do not be fooled by its pretty bloom. The plant is a monoculture that just wants total control.’
Getting rid of this garden bully is not easy. A good fork and spade are essential, but you may need more. You could pay a professional £100 to do your dirty work.
Guy Barter, chief horticulturalist at the Royal Horticultural Society, says: ‘You can spend the better part of a day getting out this shrub, digging a 2ft trench around it and then levering it out. To avoid breaking a favourite spade, a crowbar can come in handy.’
If a stump is too big to pull out you can paint it with herbicide containing glyphosate, such as Roundup Tree Stump & Root Killer. It will be £15 well spent.
This rhododendron was first imported from the Mediterranean in the 1760s. It provided excellent cover on country estates organising game shoots of partridge and pheasant.
RUSSIAN VINE
THE vine is seen by many homeowners as a quick fix for a bare garden or to block out a view of the next-door neighbour. It can be bought from a local garden centre for about £20.
The plant (Fallopia baldschuanica) has the nickname of the mile-aminute vine, and can grow by as much as 13ft in just a year.
It is easily recognisable due to its long clusters of creamy white small flowers that cover the plant over the late summer. But while it looks attractive the foliage can take over the garden, choking all the energy from other blooming plants.
Guy Barter says: ‘An awful lot of Russian vine grows in people’s gardens. If you pull it up do not throw it on the compost heap or over the fence because it could take root.’
Introduced in 1884 as a climber it proved popular among gardeners in the 1980s and 1990s.
Unlike other non-native species it is gardeners that do most of the spreading of this fast-growing vine.