Japanese Knotweed – just the name sends terror through people. Introduced by Victorians as an ornamental plant that could stabilise riverbanks and railway embankments it has managed to find its way into all sorts of corners of our towns and countryside costing the UK economy around £150 million per year in control measures. Successfully eradicating knotweed from the Olympic park in London cost £70 million (getting on for a pound per person living in the UK) and took several years! There are companies whose sole businesses is its removal, councils employ teams or officers to attempt to eradicate it and if it grows in the garden of a house you want a mortgage on, forget it. It is common on sites that are disturbed by human activity – railway lines, old rubbish tips and derelict land, being spread with loads of rubble, soil and rubbish. It also spreads along watercourses and on machinery and vehicle tyres. Growing 3 centimetres per day, it displaces other plants and is and able to break through concrete! This is about as close as to triffids as we get! Watch time-lapse photography of Knotweed growing a metre in three weeks here.
Why mention it in a foraging blog? Of course you can eat it – but. Yes – a few big buts:
1. It is an offence under the Wildlife and Countryside Act 1981 to introduce Japanese Knotweed to the countryside. Just a small fragment of root can spread the plant. Handle it responsibly.
2. To control it, sites may be sprayed with herbicides.
To avoid falling foul of either of these points:
1. The plant is spread during ground disturbance and fly tipping. However, it is recommended that any waste (stripped leaves etc.) should be boiled / burnt and then binned – not put in your compost!
2. Check for any notices showing it has treated and look for signs of unhealthy (wilting / yellow spots etc.) vegetation.
You should also note it is rich in oxalic acid and if you suffer from gout you should only eat small quantities of it or avoid it.
If you have still want to eat it what are you in for? It is rather like rhubarb – “Rhubarb but nicer” I’ve heard from many I have fed it to; less tart than rhubarb.
If it gets too big it will be stringy and not good eating. Aim to pick it around now. You should be looking for bits that are about 30 cm high or just the last 30 cm of taller bits. Cut them off with a knife. Back in the kitchen, strip any leaves and scrape off the papery tissue that divides the sections of the stem. Tough pieces will need peeling.
Among the things you can do with it:
- Vegetable – stir-fried, braised
- Puddings – Knotweed Crumble, Fool, Cobbler, Ice Cream..
- Fruit leather
- Knotweed muffins
- Jam, jelly, marmalade
Japanese Knotweed is also rather good for you containing high levels of vitamin A, vitamin C, certain antioxidants, potassium, phosphorus, zinc, manganese and resveratrol, the substance in grape skins and red wine that lowers cholesterol and reduces the risk of heart attacks!
If Japanese Knotweed is continually cut (and eaten) it will eventually give up – a far better way of controlling it than gallons of chemical sprays. In fact, some US authorities have given up trying to eradicate it and instead run annual Japanese Knotweed festivals!