Removing Invasive Plants from Stanley Park

   Vancouver, British Columbia, Canada

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Knotweed


Knotweeds (Polygonum spp.) are an economically important problem because they can grow through concrete, streets, and foundations. They grow an extensive thick root system which regenerates plants from cut segments. Digging up those roots may be impossible because they grow under rock and concrete. The plant looks like a bamboo, with jointed hollow stalks growing from a crown, that dry out in fall. The roots can be identified by their red colour. The floppy heart-shaped leaves are also easy to spot. Those in Stanley Park have a concave base with red veins in early spring. Their exact species is debatable, probably Bohemian.

Stanley Park invasive plants - Japanese Knotweed Stanley Park invasive plants - Japanese Knotweed

Never mentioned on the web, are the low tussocks of tightly packed leaves,that grow without any upright cane. At most they have foot-long trailing stems. These leaves are much more narrow and pointed but the concave base is the same give-away. Many times there is no single tap root, but a mass of tiny roots. Other times, along with the mass of tiny roots, there is a single thread leading down to a deep larger rhizome.

The 2011 Ecological Action Plan (page 10) funded $12,000 for a three year course of chemical herbicide. In spring 2017 (six years later) all sites still had healthy growth (I could not find sites #8 and #10). Evidently either chemicals don't always work or their application by Parks was too inefficient.

The inter-intra-city organization created to deal with the really bad invasives (ISCMV) produced a Knot On My Property brochure for the public. I believe its advice is very bad. They tell you to attempt nothing yourself. Their only solution is to hire professionals with access to chemicals. Why? (1) Because supposedly you are incapable of collecting and disposing of plant material, and (2) because they imply that all root systems are too large to dig out. I think both arguments are garbage and counter-productive.

With most invasive plants, information on the web is full of doom and gloom, predictions of failure, and excuses for inaction. Example for Knotweed ..."Reproduction can occur from as little as 0.7 grams of stem or root tissue. Buried rhizomes can regenerate from depths up to 1 m, and are able to remain dormant for many years." For other species I have found a big difference between claims that something 'can occur' and what actual does occur. But I am finding that the warnings are indeed correct for Knotweed. I found a one inch piece of thoroughly rotted root sending out a healthy shoot after lying exposed on a rock, in heavy shade for a year. I am still finding new shoots from apparently dead plants, after three year's dormancy.

............. How to Clear ..................

Your first step should be to use a hand cultivator to see just how large the root is, and dig it up if possible. A few minutes and the job is done ... while ISCMV is still repeatedly spraying the same plants 7 years later. At least half the plants I have dug up, had roots small enough to remove intact. I would not suggest using a spade because the roots are pulpy and easily broken. Even the force from tilting a hand trowel is sufficient to break the root - leaving you to fish around for what was left. Yes there is the possibility that you leave a bit of root behind, but so what? Dig up the much smaller resulting plant when/if it appears.

I have found many plants that I think of as 'exploratory'. They are single stems rising from a very thin tiny thread of a root that can travel long distances from the nearest established plants. I think these are last ditch attempts by a stressed plant. I saw no reason to not pull up these plants along with as much of the root I had patience to dig. Only twice has there been repeat growth. I have been leaving rock salt used for winter de-icing in the hole, to stress the remaining root. (Documentation has shown some success from flooding plants with sea water.)

For those plants with roots too large to dig up, the second choice is to inject chemicals either directly into the root, or into the hollow base of the bamboo-like shoot. Spraying chemicals is obviously far less effective and more dangerous. It does have an advantage though, when there are dozens of stalks. The application rules limit the chemical per area, so that limit is quickly used-up when there are multiple stalks to inject. Wiping the leaves uses less chemicals/stalk than injection. In Canada, access to and permission to use these chemicals is restricted to those who complete an extensive training in the use of all chemicals. So this method cannot be used by the pubic.

There is plenty of web advice saying that weekly knocking back of new growth will eventually exhaust the plant. This is mostly true but be prepared for a 3 or 4 year program. Originally new shoots were fast growing and re-sprouting. That slowed within the first summer. Some plants gave up after one or two years, but others continue to sprout. Now some roots only show growth once in the spring. Leaving rock salt at the sprout points definitely helps. I leave any root partially dug up exposed to the sun in order to create stress and dry it. This allows me to spot new buds of growth immediately. I am guessing that the only thing accomplished by breaking off the root would be to trigger the remaining plant to expand in another direction. I found that slicing off the top of the crown delayed re-growth, but I worry that by doing so the root is more likely to sprout elsewhere.

Covering large areas with a tarp, landscape fabric, or old carpet, accomplishes the same thing as knocking back - it limits the plants ability to photosynthesize with leaves. Parks has refused my request for landscape fabric at spot #6. The one spot they previously used fabric (#11 a decade? ago) was never maintained. But after I cleared the limited growth through the fabric, there has not been any re-growth. Obviously this method requires maintenance. I believe Park's refusal to use it now, is based on their self-determined failure at #11.

............. ISCMV Chemical Spraying ..................

ISCMV's last visit was in 2017 and even then they seemed more interested in erecting big signs extolling themselves. They have no game plan for the individual sites. They won't dig up roots, saying " there is only one site in the lower mainland that is sanctioned for mechanical control by the province." They tell volunteers to not knock-back growth because we cannot be trusted to continue for the necessary time period. They won't inject chemicals into either the stems or roots - just spray. They won't use landscape fabric where spraying is obviously pointless.

They are being paid to simply show up and spray without thinking, caring or taking responsibility ..... a waste of taxpayers' money, with the huge downside cost of allowing politicians to wrongly believe the problem is being taken care of.

In 2020 there are remaining plants that absolutely need a program I cannot provide - salt and tarp at #6, and repeated blackberry clearing at #8. The problem is that ISCMV does not show up most years, even when Parks tells me they will. So after leaving a plant to grow (producing leaves for the spray to work on), I was left with a newly re-invigorated root system that will take another 4 years to kill. ......


Stanley Park invasive plants - Japanese Knotweed

............. Work at Specific Sites ..................

  1. This area is the circle created by the equestrian bridge ramp. It was a huge infestation at the start. Since spring 2017 when I started, there have been about a dozen different attempts at re-growth, in different years, at different spots. Six had root systems I believe I cleared. At others I could not clear the root, but there has been no re-growth.

    Two exceptions. There is one problem plant outside the circle by the pillar. This was an exploratory plant, but after digging it up in 2018 it has reappeared in 2019. It needs chemical spray. Also in 2019 shoots have pushed through the tarmac path. I decided to leave these for chemical spray, but of course the sprayers never showed up.

    The major problem now is that the plot has been colonized by Bindweed, which is just as much a problem. Spot #1 is right in the middle of a huge wild area (both east and west of the causeway) that is otherwise clear of Bindweed. So this point source of further contamination is a major problem. If ISCMV did indeed spray chemicals in July '17 (as their sign said, but no evidence) the chemicals did nothing to kill the bindweed.

  2. This is a marshy area with only speckled sun just beyond the trail paving. It spends many winter months under water. Each year I have found sprouts attached to roots never more than 6 inches deep. Each time the root seemed to be isolated. Two were individual tussocks, but the others were short lengths of root - as if they had broken off from some other larger root mass.

  3. Behind the left bench, against a tree, one plant is growing from a root that I believe travels under the tree root to the right. There have been exploratory shoots every year, off in different directions. I am digging up the partial roots I can, and leaving salt in the holes.

  4. This area has huge, extensive roots growing into the bank. Originally I cleared two plants from up the gully and another two from the bottom. But there were two other roots still sending up sprouts, that were too big to dig up. I left as much root exposed as possible and knocked back growth weekly. I am using salt on the horizontal sprouting sites. Now they are sending up shoots, if any, only once in spring.

    But there are remaining small roots underneath the tarmac on the slope, that continue to send up sprouts. These should be treated with chemical spray, but since that won't happen, I continue knocking back weekly.

  5. This area is between the first 1bench - 2bench combo. The chemicals had worked on the crown at the north end, until it re-sprouted in 2019 after at least 2 years of dormancy. I dug up and cleared the root. I dug up all the root of another crown half way between the benches, in 2017.

  6. This wet grotto is a major problem. In spring 2017 I dug up individual plants growing in the dry soil at the entrance. There are also exploratory plants developing out of the dry bank. Their roots are hidden inside the steep bank protected by a log. Cutting away the log would destabilize the bank. ISCMV sprayed in 2017, but there was regrowth in 2018. ISCMV never turned up that year after promising to. I continue knocking back weekly.

    The inside of the area is dripping wet all year round. Chemicals are pointless (and off label) unless injected but ISCMV still sprayed in 2017. In late fall '17, after three months without rain, most of the dripping had stopped, so I did a comprehensive dig to remove all possible roots. The 'soil' remained sodden. This makes it impossible to see or feel the roots. In some places the roots have traveled through cracks in the sandstone rock. Pulling away the rock could compromise the cliff, so I don't feel free to do so without permission (which I know would be refused). I knowingly left behind lots and lots of roots.

    Landscape fabric should be used - all other methods have been tried - but that method seems to be on ISCMV's 'we don't do' list. I requested that Parks drop off a bolt of fabric for me to install. They refused. In the spring of '18 the roots I had dug the prior fall and left to dry in a pile, were clearly still viable and sprouting, so I bagged them, leaving the bags for Parks to pick up for disposal. Parks dumped out the contents of the second bag in spitefulness and took away the bag itself.

    There is nothing more that I can accomplish at this site. It needs a) rock chipped off to get at hidden roots, b) a layer of salt, and c) a tarp.

  7. This spot is just south of the steps. The chemicals had killed two crowns in front when I took over. I dug up an active third one in between the two. In July 2017 ISCMV sprayed a fourth plant growing from a crack in the rock wall. In spring 2018 there was healthy new growth. I knocked a lot of the root out of the crack, but not all of it. This would be the obvious place to simply block off sun to prevent regrowth. But Parks vandalized my packing 3 times, even though I left notes asking them to leave it and identifying myself.

  8. Originally, I could find no remaining evidence of this spot beside 3rd Beach - just north of the bike rack. I thought the chemicals must have worked. My request to Parks for confirmation the site had been cleared was ignored. In spring 2020 Parks weed-whacked the blackberries back a few yards, exposing about a dozen plants. I dug up about half complete with roots. I have no idea what Parks has planned for the rest. They certainly won't maintain access through the blackberries, either for knocking back growth or for spraying. They could use a shovel to expand the holes I have dug - no downside. But Parks just doesn't do physical stuff like that.

  9. Just around the corner from the top of 3rd beach is a grassy area with multiple plants throughout, but mainly at the south end. I dug up about 6 plants successfully, roots and all. Another only sprang to life in 2019, after 2 summers of dormancy. Another 6 had roots too big to dig, so I repeatedly knocked-back new growth and used rock salt. I believe they have now given up.

  10. I could find no remaining evidence of this spot near the lookout above the gun tower. The chemicals must have worked. My request to Parks for confirmation the site had been cleared was ignored.

  11. There are three sites here. Site A is a large grove of about a dozen mature plants at least 10 feet tall, back from the path up the hill and inaccessible behind blackberries. ISCMV sprayed in 2017. There has been no regrowth as of 2020.

    Stanley Park invasive plants - Japanese Knotweed

    Spot B, back from the trail, is a void surrounded by Blackberries. You can see where the plants used to be because no other plants have been able to grow on the evidently sprayed site. It appears that the chemical spraying worked.

    Spot C was covered in landscape fabric at some time in the past. But it was not maintained. The Knotweed grew through the fabric, leaves fell and created new top soil, grasses and blackberries colonized the new soil. There was also Knotweed growing from crowns in the new soil, sending out roots sideways because they cannot go down. The blackberries then prevented any maintenance.

    In 2018 Parks weed-whacked part of the blackberries, giving me access. I cleared all the plants living in the new soil and the accessible plants outside two edges. Unlike any other spots, the plants growing above the fabric are connected, not by rhizomes, but by old hollow stems. This might be because the area was used to pile salvageable logs during the windstorm clean up. Those logs may have pushed stems down into the ground, prompting them to root themselves. That would mean the fabric was laid before the 2006 storm.

    In 2019 Parks weed-whacked more of the blackberries. I cleared the plants in this north area, except for three outside the area of fabric. One is far under a fir tree behind a bank of blackberries so I had to leave untouched. One at the back, behind blackberries, I cleared as much root as possible, but I don't think I got it all. The third at the front/north I could not clear, so I made my own cardboard barrier to prevent regrowth. The regrowth of blackberries may prevent my maintaining it.

    Further back behind spot C, under a large fallen tree, one plant is still sending up healthy shoots (only a few weeks after ISCMV sprayed so they must have forgotten this plant). I dug down about a foot without finding the bottom. After it got missed in the 2017 spraying, I initially covered it with a dark-out bag. When that did not stay put, I broke off the end of the root as low as I had dug. So far in 2019 it has not re-sprouted.