Where did Knotweed Come From?Japanese knotweed was introduced to the UK as an ornamental plant and as a fodder plant. A specimen was sent to Kew Gardens around 1855 although the London Horticultural Society apparently obtained a specimen around 1825 (under the scientific name Houttuynia cordata). This date is supported by an article in the French journal Revue Horticole (1858) which reports that Japanese knotweed 'has been cultivated for twenty years in the garden of the Horticultural Society of London'. This specimen apparently came from China and was planted in an artificial swamp at Kew. Japanese knotweed was soon discovered to survive on dry ground and was recommended as a plant for the back of the shrubbery or as an isolated specimen in a part of the lawn. By 1850, the plant had been given the scientific name Polygonum cuspidatum (Siebold and Zuccarini). The invasive nature of Japanese knotweed was soon observed and by 1905 the Journal of the Royal Horticultural Society no longer advised such planting unless it was 'most carefully kept in check'.
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Why is Knotweed so successful in the UK ?The simple answer is that Knotweed has no natural predators to knock it back and compete with it here in the UK. In Japan and other Asian countries it's assaulted above ground by aphids and has to compete with fast growing grasses and bamboo stands while below ground it is often attacked by native fungi. In the UK Knotweed is such a fast grower that it quickly overpowers native flora simply by its aggressive growth strategies. It quickly shades out slower plants and its root system allows it to overwinter successfully and re commence each season.
Why Knotweed is like an Iceberg?They say that 90% of an iceberg is visible beneath the water surface and in this sense knotweed has the characteristics of an iceberg. A large amount of the biomass of a knotweed stand is hidden beneath the surface and these roots are highly resistant to damage and attack. You'd be forgiven for thinking that knotweed spreads by broadcastings it's seeds each autumn and then they germinate each spring. Not so with Knotweed. Due to the nature of the varieties of knotweed in the British Isles reproduction by seed is not possible as all of the viable Japonica Fallopia plants are female and the only viable male plants discovered so far have been hybrids, so this blocks the seed route of reproduction in the British Isles. So how does it spread then? The answer is vegetatively, through its roots. The root system of a single knotweed stand can reach 7 meters/23ft horizontally and 2 meters/6.5ft vertically. The biomass of a knotweed stand can weigh as much as 14,000 kgs in a hectacre/2.5 acres . Spreading underground isn't the only means of transmission. These roots or to give them a better name of Rhizomes are 'infectious' in the sense that fully viable knotweed colonies can establish from a really really small fragment of a single rhizome. This is the principal reason why anyone dealing with knotweed should be very aware of the risk of accidentally spreading knotweed with your spade, hoe, rotavator or by carrying fragments of the Rhizomes on your boots and 'wellies. These rhizomes have been responsible for the spread of knotweed throughout the UK and Ireland. Above ground stems are also capable of regenerations with tests proving that 8-12 inch lengths of cut stems can regenerate successfully
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Can Knotweed damage my property?This is a complicated area in terms of trying to quantify the damage knotweed can do. Let's separate fact from fiction for a moment ?. Can knotweed crack my foundations, rip through reinforced beams and possibly cause my home or building to crash to the ground? No or at least in all the projects we have ever attended to we've never seen major structural damage caused by knotweed. Can knotweed invade cracks in my foundations, penetrate openings in drains and ducts, block drains, spring up through cobbles, spread along my lawns and flower bed, cross from my grounds into neighbouring grounds with alarming speed and stealth and store up potential liabilities for a property owner? Yes indeed it can.
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