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. These are not a result of root pieces left behind after digging, because they have sprouted in the areas where no work has been done other than chemical spaying. I don't know if these become bamboo stalks in a second year.

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 dire 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, three years later.

............. 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 in my three years 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. Now in my third season this has worked on only some roots. 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 many 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.

Covering large areas with a plastic tarp accomplishes the same thing as knocking back - it limits the plants ability to photosynthesize with leaves. Parks has refused my request for landscape fabric, and the one spot they previously used fabric (#11) was never maintained, so I cannot say whether it works better than knocking back. Obviously it has to be maintained by pulling back at least yearly to clear soil and plants from growing through and on top, and to knock back growth occurring below.

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

Their one visit in 2017 shows that they have no game plan for the individual sites. They won't dig up plants. They won't inject chemicals into either the stems or roots. They won't use landscape fabric. Their Graham Watson tells volunteers to NOT clear because physical work needs to be 'sanctioned' (and they says only one site in the Lower Mainland is). 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.

They never showed up in 2018. In late summer I had found a new plant and had to decide whether to dig it up or leave for spraying. I requested confirmation they would visit, and was told they would. So I left it and it regained all the vigor I had been trying to deplete.

In 2019 there are remaining plants that absolutely need yearly injection/spraying ...... not just sporadically after plants regain their vigor.
At #1 Spray the exploratory plant outside the ring, by the pillar, that has re-appeared after I dug up a previous year. Produce a game plan for the plant growing through the tarmac of the path close by. It needs to be marked and protected from traffic so that there ARE leaves to spray...... or else coordinate with volunteer to knock back (who will actually do so).
#3 Spray the plant growing from under the tree that cannot be dug up. Check for any exploratory plant off to the right.
#4 Spray the regrowth from the vertical face of the slope, where digging would de-stabilize the slope.
#6 Check if there is growth on the outside slope of the bank, that can be sprayed, where digging would de-stabilize the slope. Produce a game plan for all the plants within the dripping wet grotto.
#7 Produce a game plan for the root within the rock cleft, since Parks repeatedly vandalizes my light-blocking solution.
#11 Check yearly for regrowth at A and B and respray without waiting for huge growth. Leave a path through the blackberries so others can check it is being done - instead of prior decisions to pull the blackberry branches back over the access.


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. By spring 2017 there were only 8 individual shoots. One was outside the circle. Two were sprouts from roots too deep for me to clear. Six had root systems I believe I cleared

    In 2018 and 2019 there were limited new sprouts in different locations, some exploratory plants from a thread, some with roots that could be cleared, others from large roots below (not crowns) that evidently had been dormant. I have been knocking back and digging up as they occur. 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. This might be just an exploratory shoot, but I decided to leave it for chemical treatment.

    The major problem now is that the plot has been colonized by Bindweed, which is just as much a problem. The spot 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 they 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. This can only be cleared with chemicals. There was an exploratory shoot in each of 2017 and 2018 off to the right side in the ivy.

  4. This area has huge, extensive roots growing into the bank. I cleared two plants from up the gully and another two from the bottom. But there are two other roots still sending up sprouts, that are too big to dig up. My July '17 request that ISCMV drill holes in the roots and inject chemicals was ignored.

    I am hoping that by exposing as much of the roots as possible, and weekly knocking back new growth, the root will be exhausted. 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. So I just knock back the sprouts and hope the plants keeps trying at same spot. I am using salt on the horizontal sprouting sites.

    In spring '18 two new sites sent up shoots from cut roots that I had not cut the year before, so others must have tried clearing here before I started. In spring '19 one sprout is coming out from the vertical hill side. It has a slab of tarmac over it so I cannot access the root. I am leaving it to grow and get the chemical treatment in the fall.

  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 '19. I dug up and cleared the root. Another crown half way between sprouted in 2017 and I dug up all the root.

  6. This wet grotto is a major problem. In spring 2017 I dug up some 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, so I finally pulled out the shoots. So far in 2019 they have not re-appeared.

    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.

    There is nothing more that I can accomplish at this site.

  7. This spot is just south of the steps. The chemicals have killed two crowns in front. 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. I could find no remaining evidence of this spot beside 3rd Beach. The chemicals must have worked. My request to Parks for confirmation the site had been cleared was ignored.

  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 am trying to kill them by repeated breaking off of shoots and rock salt. About 3 of the 6 seem to be dead, but 3 continue sprouting. There have been about 3 exploratory shoots that have not reappeared. My July '17 request that ISCMV drill holes in the roots and inject chemicals was ignored.

  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, a bit back from the path up the hill. ISCMV sprayed in 2017. There was no regrowth in 2018. In 2019 there is too much other growth to see what is happening on the ground.

    Stanley Park invasive plants - Japanese Knotweed

    Spot B, back from the trail, is now grown up with Blackberries. I have not investigated because access is difficult. You can see where the plants used to be because no other plants have been able to grow on the sprayed site.

    At spot C past SPES efforts have created a criminal mess. It seems that long ago landscape fabric were laid over a very large area ..... and then nothing was done to maintain it. The Knotweed grew through the fabric, leaves fell and created new top soil, grasses and blackberries colonized the new soil. So now we have fabric I cannot pull up. Under the one edge I found there are healthy Knotweed still growing .... but I cannot get access to dig out.

    There are also Knotweed growing from crowns in the new soil, sending out roots sideways because they cannot go down. And also Knotweed growing through the fabric. I believe I have cleared all the plants living in the new soil and the accessible plants under one edge. 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.

    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.