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Japanese knotweed

 
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Hello everyone, I recently bought a plot of land I plan to cultivate a small native plant nursery on. Unfortunately the edges are overgrown with black locust and Japanese knotweed. does anyone have any advice on clearing this land?
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gardener
Posts: 289
Location: Central Indiana, zone 6a, clay loam
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Hello Colin! Congratulations on the new land! Ah, the Japanese knotweed. It is a powerful plant, but it can be managed. How large is the area where the knotweed is growing? How large is the property overall?

What do you think the knotweed and black locust might be telling you about the soil in that area?
On our land, we found the greatest density of knotweed in the most compacted, clay heavy soil. It even broke a rock it wanted to grow through!
Since it sounds like the knotweed is on the edges, I would just mow or machete it frequently. It will take time, but if it never gets the chance to photosynthesize, it will weaken and die eventually.

Its roots can extend quite a distance from where you see shoots. I would be extremely cautious about transplanting other plants in the vicinity to elsewhere, lest you inadvertently spread knotweed to other properties. Maybe make a habit of either growing in containers or removing all soil from the roots of plants grown in the ground and checking for knotweed roots before sending them elsewhere. I would highly suggest familiarizing yourself with what the roots look like so you can be sure you aren't spreading them. They can regrow from very small root fragments.

For perspective, the land where I live has quite the Japanese knotweed presence. Probably about a 40 foot diameter circle of it. We are unwilling to use poison and it doesn't sound like it works that much better anyway. We have tried several tactics over the past two years we've been managing it. It is still present, but we have learned a lot and it does seem to be weakening considerably. We chose to site our garden where it grows, partially because it would encourage us to stay on the knotweed removal. At first, we tried eating it. Tasty, but couldn't eat much before the high oxalic acid content became apparent and unpleasant. We picked tons of shoots in the early season and sold them to a fancy restaurant. We cut down their stalks as often as possible, but definitely before they could flower. We eventually decided to dig out the largest clusters of them and then burned them along with all the honeysuckle we cut over the spots we dug them from. We spent a lot of time tracing the smaller roots and digging them too. Since all that, we have just been pulling the shoots as soon as we see them to stop them from photosynthesizing. If I had it to do over again, I wouldn't have wasted my time with tracing down smaller roots. I do think digging out the largest clusters of roots was worth it. Though I really wish I'd either dried them or made them into a tincture, as Japanese knotweed root has many medicinal properties. Honestly, I think that continual cutting is the best strategy. Surprisingly, growing pumpkins over it was quite helpful in setting it back too. They out competed it for resources enough that it rarely got above the pumpkin leaves. It seems too that the more we let other "weeds" grow that break up compaction, the less successful the knotweed becomes.
 
Colin Dodge
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Thank you, the total size of the property is about 1/2 acre. The part I just bought is a 1/4 acre behind my house that's the  part I'm using as a nursery field. It's separated from my home and yard by a concrete alley that's about 15 feet wide. so far the knotweed has not been able to cross this barrier. I bought the land from the city, they had been mowing it with hug tractors but they couldn't get close to the alley or fence lines do that is where the knotweed and locusts are coming up.
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pollinator
Posts: 180
Location: Japan, roughly zone 9b - wet and warm climate
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Apparently goats love it. We call the plant itadori here. My friend has a goat and happily took the cuttings from some growing in our lot to feed it.

For us humans, you have to process it to eat it safely, but it's a decent vegetable companion to serve with meat and rice. Here's a recipe for the basic preparation in Japanese. https://cookpad.com/recipe/2668885

You can use Google translate to get a decent translation.

Very roughly summarized: cut off the tops. Make an incision in the skin and split/peel it with your fingers. Boil it in barely boiling water for three to five minutes until it changes color as pictured in the link. Then take it out and cool it in water, changing the water until it's cooled. Then leave it in the fridge overnight.

It doesn't say so in the recipe here because it's "common knowledge" but you usually only harvest the young shoots that are the size of typical grocery store asparagus.
 
Colin Dodge
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I was thinking about clipping it down to the root and then seeing if chickens will tear up new shoots as they sprout does that sound like a good plan?
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