Knotweed: the opposition

Local man battles Japanese Knotweed in his yard


OLYMPIA –– Even in human time, it hasn’t been long.  From the beginning until now, it’s been a bit more than two months.  The battlefield is the empty portion of the lot we live on.  Until it was purchased last year and cleared, it had been the home of a well-entrenched patch of blackberries and much larger, thick patch of tall, Japanese Knotweeds (our words –– I don’t know what the Japanese call them).  The knotweed patch is about 40 feet by 70 feet.  This spring, both the blackberries (20’ by 40’) and the knotweeds came back with gusto.

I had prior experience with knotweed at our place in Mason County.  We sought the assistance of the County Extension Agent.  She had me clear the patch we had, cutting the 45 bamboo-like stems off at the ground.  She then came around and with a large syringe and injected each stem base with a chemical.  After a few weeks, she came back, checked the plants, and told me I could now start a low fire on the injected stem bases and keep it burning for a couple of days.  It worked. 

Now, five years later, I live in Olympia.  When I checked with Thurston County, I learned that they did not allow chemical removal of weeds.  The master gardeners suggested we pull out or cut the new growth at ground level and place a plastic tarp over the plants, preferably two tarps one on top of the other with weights around the edges.  Then, wait two years and they would be dead. 

When I called the City of Olympia Waste Management Office and asked them for advice about what to do with knotweed detritus, a very helpful woman said, “Please do not put it in your Yard Waste bin. You must dispose of knotweed only as garbage.  You can put it in your garbage bin or you can haul it to the waste management site and dump it in the proper hopper.  It all goes into a landfill.” I decided to dig it up.

I bought a shovel for the job and spent three hours a day for ten days, digging up the knotweed.  I started at one end of the patch and worked back and forth across it.  Early on I was digging on the border between our place and the neighbor’s.  I saw there were some knotweeds growing on his side and thought I would do him a favor.  About twenty minutes later, Tom came out of his house and asked me to stop.  

“The first thing you should know is that you’ll never get rid of ‘em,” he told me. “Besides, I just planted grass seed here and you’re digging it up.’

I was only trying to help. He then suggested that I do what he does.  

“If you mow it once a week or so, it’ll keep them down,” he said. “Trust me.  You can’t beat ‘em by digging ‘em.  They just keep comin”.

I apologized once again and, since his lot had maybe 15 or 20 shoots coming up and we had hundreds, I went back to digging on my own turf.  By the time I had cleared all the knotweeds in that first 10-day run, I dug up about 750 pounds of shoots and roots.  I also felt like I was well on the way to being a hands-on knotweed “expert.” 

By the time I was done with this first assault, new shoots were four or five inches high at the end where I started and of lesser heights up to two-thirds of the way to where I had finished.  Three weeks later the entire space I cleared was covered with a healthy new crop from two to fifteen inches tall. 

This may be an appropriate place to admit what may have already occurred to some of you.  Knotweed eradication became at a minimum a minor obsession.  Every day for ten days, I had been out there continuing my attack.  Now, as I surveyed the new community bursting forth, I vacillated between thinking of myself as a determined conqueror and a quite successful knotweed nursery manager. 

On one hand, I was deciding how tall to let the new crop get before I launched a second assault.  On the other, I was both pleased with the new growth and amazed at how resilient the plant is.  If good-hearted human beings were this persistent and this determined, maybe, by now we would have put social inequities behind us.    

What to do? I waited another week and then started the second assault.  I found that some of the taller shoots in the reborn group had as much stem under the ground as above it.  It meant that they were there the first time and I had missed them.  So, I went deeper.  This attack was more intensive, because I was going deeper –– 15 inches, and leaving no visible bits in the ground. 

It took longer this time because my digging was interrupted by my birthday and father’s day, but as of today, with only about 10 square feet of the reborn remaining, another 630 pounds plus half of two garbage cans have gone to the landfill.  I would guess the total will be approximately 1,200 to 1,300 pounds.  I have been visiting friends in Eugene for a few days.  Tomorrow, I will finish the job.

It has taken a little more than three weeks to get this far and, Shazam, the second rebirth of the modern era is well underway.  So, my strategy changed.  The current plan after I clear the remaining reborn patch, is to: 1) pull up as many as I can; 2) rake the soil; 3) plant the whole area with grass seed: 4) pull out the most aggressive knotweeds while the grass is growing and until it is high enough to mow; and 5) adopt Tom’s model of knotweed management – mow the enemy down!

There is one niggling little concern, however.  If the tops of the plants are mowed off, the stem lives on and a new shoot grows.  Mow it repeatedly and the in-the-ground stem just gets bigger in girth and more firmly entrenched.  Patience is another of its virtues and it will wait.

With about 80 hours of knotweed digging, pulling and hauling experience spread over three months, I developed a profound appreciation for their persistence and resilience.  Although I may be kidding myself, I am prepared to say that with the combination of hands-on engagement and with some pretty well developed observation skills, I think I have learned quite a lot about these truly incredible plants. 

Below is some of what I think I know:

  •   Knotweeds have the capacity, like fungi growing on different trees and logs, to grow from a number of different kinds of plant roots.  In my recent study, their favorite adoptive root is that of the blackberry plant.
  •   With knot weeds, root size doesn’t matter. I dug up a root about a foot long and about 3/16” in diameter.  At one end, lined up so they were touching each other, were seven shoots.  At the other end was a single one.  I have photos of two pieces of root; one is a little over two inches long, the other just over three inches, both about half an inch in diameter.  Between them they had 17 shoots straining for the sky. 
  •   Casual observation shows one that knotweeds have segmented stems a bit like bamboo.  However, the two are not related.   The fibers in knotweed stems are softer than, and not as strong as, bamboo (flooring, if it could be made from knotweed stems, would not last like bamboo does). There are three main varieties and, while some produce seeds, they may not be viable. 
  •   It seems to me that some sort of airborne bits (seeds or stem parts) carried by birds or the wind, have to be part of their distribution scheme. We know they regenerate from roots in the ground. We know they were brought here , quite likely as decorative plants.  Bits could be purposely or unknowingly carried from one place to another by humans or animals (we have regular visits these days from a doe and a fawn, who like knotweed leaves very much). However, when they are young, and especially while still in the ground, any stem segment of a shoot can become a plant.
  •   Knotweed leaves fall off in autumn.  Bamboo leaves grow and fall off throughout the year in irregular patterns depending on the weather.  In my experience with black stem bamboo, more fall off in winter than at other times.
  •   Cutting a shoot (technically, a rhizome) off at the surface or pulling the stem out of the ground without separating it from the root does not kill it.  As long as a shoot remains connected to a root and that root remains in the ground, it will grow a new plant. I am not certain if individual segments that break off from a stem and fall back into the ground can grow a plant.  I don’t take any chances.  In the second sweep, I carried an old five gallon paint container just for the little bits and pieces.
  •   Shoots can grow one from another.  A new shoot can start from a segment of an existing shoot shortly after the first shoot starts growing and has just two or three segments.  New branch segments can be launched later as the parent shoot seeks the sky. I found branched shoots from close to the root and anywhere else along the way to the surface.  

To know your enemy, first, know yourself. I still have some work to do on myself and on the knotweed. 

After more than two weeks without digging, today the last little square is gone.  Two friends came by and they did the corner, and I went after maybe a hundred random plants.  Remember, some of these began returning just days after my assault left their area “clear” of any plants. Others returned in the last two weeks. And they survived an above-ground weed wacker attack by Terry, who mows the lawn every week. 

For the dedicated eradicator, every intimate interaction with knotweeds turns into a learning experience.  Hence, the following addition:

  • Going deep and leaving any knotweed remnant or random root bit in the ground, even the most innocent looking, small piece of who knows what plant root, means that the next wave of arrivals, and there will be one, will get their start close to the surface.  Today I found most of the ones I did dig up for “scientific purposes” sprung from root bits less than five inches below the surface.  If you are serious, you have to take all the would-be-knotweed root bits. 
  • As though I were an archeologist digging through ancient ruins, I was slow and gentle with the spade.  As a consequence, I found several left over random bits of whatever root with a Skyfinder shoot extending four or five inches to the surface and beyond and, departing for the same bit, a nutrient-seeking root shoot of the same dimensions, (which I named ‘Groundholder’) driving its way down into the depths.  They were clearly intending to stay.

Phase whatever-it-is begins tomorrow with clover seed, watering, precisely targeted individual Skyfinder removal missions, and, when the grass is up, weekly mowing for the rest of time.


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