Edible – Japanese Knotweed & nutty knotweed nibbles (recipe)

There is no other plant that separates foragers from gardeners more than Japanese knotweed. This — the number one most invasive plant in the world — was bought to the United Kingdom by Dutchman Dr Phillipe Von Siebold in 1850. It has since sprawled across much of Europe, into Australia and is now spreading its way across the United States.   

A forager friend told me about Japanese knotweed, stating that it was rather like Tesco/Wallmart, “popping up in places it was not wanted and taking over.” If you find this plant growing on your land and you want to remove it before it destabilizes your house or takes over your garden, then you have to dig down at least 32 feet/10m and across around 16 feet/5m, lay down an impenetrable membrane, and incinerate the soil you’ve excavated. Even if you did want to spray it to get rid of it, you would have to use a huge amount of herbicide and inject it right into the plant over a few years.  Cold or heat doesn’t kill it either, as in its native Japan, knotweed likes to live on the edges of volcanoes, meaning it can withstand total extremes of temperature.    

It’s bad news if you do find some in or near your garden. However, if you are a fan of rhubarb, there is some saving grace, as there is a very similar flavor between the two plants, though knotweed is far earthier and without the tang that reminded me of the overdose of the stuff I received as a child. A forager friend let me in on the secret of how delicious it is, and I spent the next few months reading what little I could find about the edibility of it. Steve Brill, the forager famed for being allowed to forage in Central Park, seemed the only other person who was eating it. I made the leap of faith having found a patch a few hundred yards from my home. I harvested as much as I could carry and filled the freezer. For the next few weeks, I tried knotweed everything and fell in love with the flavor. My favorite is Japanese knotweed cobbler, and I served it up with some cooked shoots protruding from the crust as if the cobbler was growing shoots of this invasive devil of a plant. This delighted and horrified my friends in equal measure.

The patch was soon built over and I had to find another. I wasn’t hard, of course, and sure enough the next season I found the mother-load: a patch so big that it appeared someone was living in it, with a sleeping bag and a packet of cookies sat in the middle of this half-acre plot of knotweed. But there was more than enough room for me to respect his or her privacy as I took tours of people around this kingdom of knotweed, feeling rather like Superman showing off his Ice Palace.

Only 10 of the 50 states are free from Japanese Knotweed.  To keep it in check check Connecticut have an outright ban of this plant, whilst other states such as Washington or Oregon have categorized it as a noxious weed and issued a quarantine order on it.       

Back in the Victorian era in Britain the railroad organization known as British Rail decided that they would use knotweed to secure embankments, and it was extensively planted next to the railroad track. I once caught a train in the far west of the UK, in the principality known as Wales, and glancing out of the window I noticed nothing but knotweed growing for at least half an hour. Here knotweed really is king.   

In both the USA and the UK you will see it growing almost anywhere; construction sites are a great spot as are riverbanks, cemeteries and anywhere that someone may have fly tipped soil contaminated with knotweed roots.

However, a word of caution: Japanese knotweed is often sprayed to the point that it’s more chemical than plant. If you spot some and know the landowner of where it is growing, then the best thing to do is ask them if they have sprayed. If not, then look out for signs of singed leaves or clumps of black roots that look like they have been charred. On municipal sites, there should be a notification sign that it has been sprayed (if in doubt call your authority). If you suspect even in the slightest that it has been sprayed, then leave well alone or risk serious illness.

The best time to go out and pick knotweed is in the early spring when you’ll find shoots coming out of the ground looking rather like asparagus or hop shoots. Harvest them quickly, as they will soon become woody and unusable. You’ll still be able to harvest the top 1 foot/ 20-30cm  of the plant until it grows to around 3 feet/1m. And note to gardeners: with repeat harvesting you can keep it in check, and if you dig up the roots constantly over a few years, you may even eradicate it. By eating these recipes you could perhaps be helping stop the spread of knotweed: who’d have thought that biodiversity tasted so good? 

Nutty Knotweed Nibbles

There is a gooey texture and a richness to these knotweed nibbles that has you coming back for more. The first time I ever baked them I sat and ate the whole batch —  think Rocky Road, or Chocolate Fondant but with buttery nuts and a twang of rhubarb instead of chocolate. 

Ingredients

3.5oz/100g butter

3.5oz/100g unrefined golden sugar

3.50z/100g chopped hazelnuts

1 tsp mixed spice

1 cup/6oz/175g light brown muscovado sugar

1 egg

8oz/225g all purpose flour

1tsp baking soda

9.5fl oz/284ml sour cream

10.5oz/300g Japanese knotweed

Method

Preheat oven to 350°f/180°c, put half oz/15g of the butter in a dish, and place it in the oven for 2 minutes until melted. Remove, stir in hazelnuts, golden sugar and mixed spice. Set aside.

Cream the butter, muscavado sugar and egg until fully blended. Cut the knotweed into small penny piece rounds, any larger bits must be chopped in half. Stir all the rest of the ingredients bar the nut mixture together. 

Place in a large round cake tin and spread mixture to be about 3cm/1 inch deep. Sprinkle over nut mix and bake for 40 minutes or until fully cooked. Push a skewer into the centre of the cake and pull it out again; if it comes out clean the nibbles are done.

Allow to cool then cut into nibble-sized pieces.