The stories of five Frankenstein plants which have invaded foreign shores causing massive ecological and economic damage.
Innocuous plants, which cause no problems in their natural habitat, can become major menaces when released into the wild in the UK.
A Rhododendron, introduced from the Black Sea area, is now choking native habitat from hundreds of thousands of acres of land in Wales and costing the National Trust a fortune to control.
It's a battle they are losing.Japanese Knotweed knows no boundaries and takes over vast tracks of land creating an impenetrable bamboo-like wall.
Even the sea is under attack.
Japweed came to the UK as tiny filaments attached to oysters bought in France and is now choking British estuaries.
But it's not a one-way traffic.
English cord-grass, not a problem in the UK, is fouling up rivers and estuaries in New Zealand and North America where the conditions and lack of natural predators allow it to grow unchecked.
Tony Russell, one of the Gardeners' Question Time panellists, looks at the battle to repel the foreign invaders and counts the cost of the war for which there are no weapons of mass destruction.
Tony Russell discovers why a single goldfish is blamed for drying up a three hectare lake and causing damage put at millions of pounds.
It's the remarkable story of the pond weed Crassula Helmsii.
In this edition Tony Russell reports on a plant that is marching across Snowdonia, is colonising vast tracts of Scotland and has even invaded Kew Gardens.
Rhododendron ponticum was imported by the Victorians, won prizes at garden shows but is now devastating thousands of acres of important countryside.
Tony Russell reports on how a grass, Spartina, suffered a freak genetic change, crossed the Atlantic and is now causing havoc in the United States.
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Tony Russell explains why poor quarantine procedures in France allowed an aggressive Japanese seaweed, Sargassum Muticum, to cross the Channel and invade waterways from the Solent to the Norwegian Fjords.