Japanese Knotweed

J A P A N E S E...K N O T W E E D (Fallopia japonica )

How to Identify Japanese Knotweed

Edible

Botanical Name:
Fallopia japonica

Known Hazards:
Oxalic acid and oxalates are mild nephrotoxic acids that are abundantly present in the stem and leaves of Japanese Knotweed (as well as such plants as fat hen, rhubarb and sorrel). They won’t cause an issue in regular amounts, but could cause a problem if eaten on mass.

Could be confused with:
Giant Knotweed (Fallopia sachalinensis) or hybrids between the two species. However these are all similarly edible too.


Range and Distribution:
Throughout the entire UK and mainland Europe from Northern Italy to Norway.


Habitat:
Roadsides, railway banks, rivers, ‘waste’-ground, and similar areas, especially in urban and suburban landscapes.

Physical Characteristics:
Japanese knotweed is a hardy, herbaceous, rhizomatous perennial.  Plants are fully dioecious, with all individuals of the UK clone being functionally female. 

Rhizomes measure up to 10cm in diameter, bearing nodes at 1-2cm spacings, and extend generally up to 7 metres from the parent plant (though distances of 20 metres have been recorded).  The rhizome penetrates downward to a depth of 2 metres or more. 

Stems can reach 3 metres high and are stout, hollow and bamboo-like with erect bases that eventually branch.  Stems are sometimes red-brown, but often green and are smooth, with thinly membranous sheath. 

Leaves are wide at the base with the tips abruptly tapering to a point.  The leaves measure 5-12cm wide and 5-15cm long, petioles 1-3cm long and stipules 8-15mm long. 

The female flower is greenish-white and drooping.  Flowers are 2.5-3mm across in dense, branched, auxiliary panicles, which are 5-9cm long.


Edible Use:
Root: (Sept- March) Starch can be extracted (with caution) and used as a thickener like cornflour.
Stem: (April-May) Young tender stem tops can be eaten raw or cooked and used as a
rhubarb substitute for crumbles, pies, sorbets, sauces, pickling, and in both sweet and savoury dishes.
Flower Buds: (May-Aug) Can be used for wine, beer, tisane making.

Herbal:
The roots of Japanese Knotweed are used to help treat Lymes Disease.


Tips and Observations:

To ensure you pick only the tender stems gently bend back the stem from the top of the plant. Like asparagus, it should snap at the tender point leaving you with a piece between 2-20 cm long. Finally, it should be noted that it is illegal to cause the spread of this plant. Therefore all off-cuts should be burnt, boiled or allowed to rot before composting – not thrown in the bin.

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