Rachel Lambert: forager, author, guide
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Japanese Knotweed (Fallopia japonica) is considered a very invasive weed in many parts of the world, including across Europe.

Here I share tips on how to turn this invasive plant into a tasty food, including information on how to do this safely and legally. I share the when, how, what and why of cooking and eating this plant. In the UK you can be fined for encouraging the spread of this plant, but not fined for eating it! Just follow these guidelines first.

Ooh, plus a simple Japanese compote recipe to get you started.

Which part of Japanese knotweed tastes best?
Experiments for Japanese knotweed recipes. Which part tastes best?!
A sign telling where NOT to pick Japanese knotweed
If treated by the council, sites are signposted. Though other sites treated by individuals or companies may not be so clear. Think twice before harvesting and definitely NOT at these sites!

When to harvest

Japanese Knotweed is ready to harvest in Spring. It can grow fast, up to 30 cm a day, so if the tips are too small just return a day or two later.

It is important that you know the plant hasn't been sprayed or treated. Here in the UK, treated sites are often sign-posted to protect people and animals, but this is not always the case. If you are not sure, then don't pick the plant.

How to harvest Japanese knotweed

It is paramount that you don't spread this plant at any stage of processing it. I normally cut the stems and put them straight into a deep, solid bag. A basket isn't appropriate for this plant, as bits may fall out and it can regenerate from a single, tiny piece.

It is best harvested when it is 1-2 ft in height, see notes below on preparing the plant as a food.

Heath benefits of Japanese knotweed

Japanese knotweed is a member of the Buckwheat family and is also known as Donkey rhubarb. Some of its other names include; Fleece Flower, Monkeyweed, Himalayan Fleece Vine, Tiger Stick, Sally Rhubarb, Mexican Bamboo, and Huzhang.

It has a sour flavour, similar to rhubarb, which also tells us it is full of vitamin C. As well as being high in vitamin C, it contains good amounts of vitamin A and may help regulate blood sugar.

How to prepare Japanese knotweed

You'll need 2 containers when you prepare this plant. One for eating, one for disposing of. The leafy tops can be bitter, so are best removed and the very base can be too fibrous. Remember to contain every part of the plant so it can't reproduce. I simmer up the bits I don't use, let them cool, then bin them.

You don't need to peel all of the outer fibre off, just the main bits. Or don't peel at all, and push the cooked stems through a sieve, discarding the fibre afterwards.

So, to summarise, discard the tops, leaves and bottoms, plus fibre (before or after cooking).

Japanese knotweed compote, cake, slice, jam, juice
Japanese knotweed compote (top left)

How to cook Japanese knotweed

Recipes to follow, I promise! Meanwhile, here's are my recommendations for using Japanese knotweed instead of rhubarb compote in recipes.

  • 300 g Japanese knotweed, trimmed and peeled
  • 60 ml (4 tbsp) water
  • 50 g soft brown sugar

Chop the knotweed up into small chunks and place in a small to medium saucepan with the water. Place over a medium heat and simmer for 5-10 minutes with the lid on. Stir if necessary. You'll now have a pulp to sweeten, start with about 50 g of soft brown sugar and stir in until dissolved. Stir into yoghurt or have with hot porridge or alongside a moist fruit cake.

Japanese knotweed recipes

For a few other ideas, such as Japanese knotweed fool, Japanese knotweed muffins and Japanese knotweed crumble, you might want to my this post; Eating Japanese knotweed.

I love to eat weeds. Many weeds are edible, abundant and available as food if we just knew, or remembered, how to use and cook them. Invasive plants are also great to eat. I always think; why curse something when you could be eating it and benefiting from its abundance? In Spring, many weeds are at their best for nutritious food, including Japanese Knotweed.

Here I describe why Japanese Knotweed is good to eat, when not to eat it and share some recipes and images (courtesy of Jake Ryan of Wise Knotweed Solutions).

Japanese Knotweed (Fallopia japonica) is both beautiful, edible and scary stuff that has a bad reputation. It was first brought to Europe in the mid 19th century by a botanist. It has been shared between botanical gardens and garden lovers for decades before the problems related to it were detected. Japanese Knotweed grows at an incredible rate and is capable of significantly damaging properties as it can squeeze through masonry and concrete. It has been known to devalue properties, growing up to 20 cm a day with roots up to 3 metres deep. Japanese Knotweed is classed as “controlled waste” and the law requires it must be disposed of at a registered landfill site. There have been cases where the environment agency have prosecuted people who failed to dispose of the plant correctly. So don't add left-overs to your compost, put it in general waste, or cook it all, then dispose of it.

Fallopia japonica

Turning a problem into a dessert

Depending on how big the weed has grown, it may be possible to add this invasive plant to a tasty dessert. Knotweed has been described as tasting like a lemony rhubarb and can be used to compliment a number of dishes. Japanese Knotweed is an excellent source of Vitamin A and Vitamin C and has also been known to prevent and treat cognitive disorders. When edible, the plant can be extremely complimentary in a number of dishes such as muffins, crumbles and more.

Fallopia japonica

When not to eat Japanese Knotweed

As an invasive weed that can cause significant damage to properties, it is often sprayed with herbicides. Before considering cooking with knotweed, it is important to guarantee that the plant has not been treated with chemicals, and to be absolute certain of this. Don’t let this put you off cooking the plant if it is chemical-free though. So long as the plant is safe to eat and disposed of correctly, it can make a great addition to a number of meals and desserts.

It is also important to remember the tasty invasive weed can only be eaten at certain times of the year. The perfect time to eat Japanese Japanese Knotweed is mid April to May when the first shoots in spring appear, are up to 20 cm in height and tender enough to eat. After that it can become stringy and may need peeling, or just look around for younger shoots. It is important not to eat the weed at other times of the year as the adult plant may cause mouth blisters. Jake Ryan of Wise Knotweed Solutions got in touch with lots of the information (including all these photos) you've just read above and recipes below, as an alternative to chemical treatment.

Fallopia japonica

Japanese Knotweed Fool

Ingredients

  • 300 ml double cream
  • 100 ml greek yoghurt
  • 450 g chopped Japanese Knotweed (leaves removed)
  • Apple juice
  • 5 tbsp unrefined caster sugar
  • Mint leaves to garnish (optional)

Method

Whip the cream until it forms peaks, stir in the yoghurt and put aside. In a medium saucepan place the Knotweed and sugar in enough apple juice to cover it and cook until tender, strain and blend until smooth. Fold in the Japanese Knotweed, pour into glasses or small bowls and refrigerate for 60 minutes. Add mint leaves to garnish.

Japanese Knotweed Muffins

Ingredients

  • 2 eggs
  • 200 ml milk
  • 100 g butter, melted
  • 300 g plain flour
  • 1 tsp cinnamon
  • 1 tsp baking powder
  • 300 g thinly chopped Japanese Knotweed (leaves removed)
  • 100 g unrefined golden caster sugar
  • 2 tbsp brown sugar

Heat the oven to 180°C and line a muffin tin with 12 paper cases. Beat together the eggs, milk and melted butter. Blend the flour, baking powder and cinnamon and pour the egg mixture into the the flour. Stir until well combined. Mix in the caster sugar and thinly sliced  knotweed shoots. Beat the mixture well before dividing between the paper cases. Sprinkle with the brown sugar and bake for 25-30 minutes or until golden.

Japanese Knotweed Crumble

Ingredients

  • 10 Japanese Knotweed stems (leaves removed)
  • 8 tbsp unrefined caster sugar
  • 1 tsp ground ginger powder
  • 4 tbsp water
  • 110 g butter
  • 180 g flour
  • 110 g brown sugar

Preheat oven to 180°C degrees and slice the Japanese Knotweed into 7 ½ cm pieces. Place the knotweed in a 20 cm by 20 cm ovenproof baking dish and sprinkle with the water, castor sugar and ground ginger. Bake for 10 minutes until tender and mix with ginger powder. To create the crumble topping, fold the butter into the flour and sugar and rub together until in resembles bread crumbs. Sprinkle the crumble over the knotweed and bake for 35 minutes. Serve hot with cream or custard, or have cold for breakfast!

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