Removing Invasive Plants from Stanley Park

   Vancouver, British Columbia, Canada

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Knotweed and Bindweed

Knotweed - results unknown

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 annual 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.

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

The 2011 Ecological Action Plan (page 10) funded $12,000 for a three year course of chemical herbicide. In spring 2017 most all the sites still had healthy growth. Digging up the roots of one plant with a hand cultivator showed very minimal root, so in mid-June I dug up all the outstanding plants numbered on the map below. Most I believe were completely cleared. In only a few spots did I knowingly have to leave behind root.

As with most of invasive plants, information on the web is full of doom and gloom, predictions of failure (to eradicate), and excuses for inaction. For example ..."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. Digging up the roots seems the most obvious first line of attack, that Parks never tried. The obvious course of action for those roots I knowingly leave behind, is to drill holes in the exposed root and inject with herbicide. But Parks would never let me near the chemicals. I am checking the numbered sites below weekly during the summer.

Stanley Park invasive plants - Japanese Knotweed
  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 6 small plants and 2 more showed in later summer. Two of the spring plants had tap roots growing too deep for me to clear. One right beside the pavement, sent up new growth in late summer. The sign posted in July 2017 by ISCMV is bogus. There were no plants at the time.
  2. This is a marshy area with only speckled sun just beyond the trail paving. The 4 plants had barely any roots at all. The signs posted by ISCMV in July 2017 are bogus. There were no plants still there. Hopefully they did not gratuitously spray just to validate the sign.
  3. Behind the left bench, against a tree, I believe I got all the root of one plant. A second plant to the right, I left root in the hole.
  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 other roots still sending up sprouts, that are too big to dig up. I am hoping that by exposing as much of the roots as possible, and weekly knocking back new growth, the root will be exhausted. My July '17 request that ISCMV drill holes in the roots and inject chemicals was refused.
  5. This area is between the first 1bench/2bench combo. The chemicals have worked on the main clump at the north end. But a young plant was growing half way between. I believe I got all the root.
  6. This is the wet grotto. I dug up some plants growing in dry soil at the entrance, and also a half dozen higher on the open ledge. I am waiting for the summer dry season to allow better access to finish. There are easily a dozen plants in the wet grotto. I will leave a second plant at the entrance for ISCMV to kill with chemicals. Its roots are hidden inside a steep bank protected by a log. Cutting away the log would destabilize the bank. ISCMV sprayed in July when the plants were dripping wet (off label) but did not spray on their second visit when it was dry (even though they were on site to take down their flagging tape).
  7. This spot is just south of the steps. The chemicals have killed two plants in front. I dug up a new plant in between the two. But in early summer a third almost-dead plant growing out of the cliff sent up a spindly shoot. ISCMV sprayed, and I later attempted to dig out the root. I could not budge it from the rock, but I did remove as much as possible of the earth that must be sustaining it in the crack.
  8. I could find no remaining evidence of this spot beside 3rd Beach. The chemicals must have worked.
  9. Just around the corner from the top of 3rd beach is an area with 9 plants growing in early summer and 3 more showing in late summer. Only one plant had been killed by the chemicals. I dug up the rest, leaving behind root in only two places. I left 6 holes not filled in so that digging farther will be easy. Counting from the north, the holes with root still at the bottom are #1 and #4. My July '17 request that ISCMV drill holes in the roots and inject chemicals was refused. They did not spray the 3 late sprouting plants on their second visit.
  10. I could find no remaining evidence of this spot near the lookout above the gun tower. The chemicals must have worked.
  11. There were originally two spots identified, B and C. This year ISCMV spotted a third site A - a large grove of about a dozen mature plants at least 10 feet tall, a bit back from the path up the hill. Their spraying brought down the front rank of plants but did not touch the deeper plants. Their fall spraying will probably do that.

    Stanley Park invasive plants - Japanese Knotweed

    Spot B, back from the trail, is now grown up with Blackberries. I have not investigated. The Blackberry root systems will make clearing the Knotweed roots much more difficult, is not impossible.

    At spot C past SPES efforts have created a criminal mess. It seems that long ago a few layers of landscape fabric were laid over a very large area ..... and then nothing was done to follow up. 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 top 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 topsoil 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. This 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. I dug down about a foot without finding the bottom. So this plant must be attacked with chemicals, or a shovel is necessary for deeper digging. There were new shoots growing when ISCMV made their second visit but they did not spray it.

Most of the sites in Stanley Parks' west side would not have been considered 'extensive' (except #11 and #1). They are at most multiple individual plant. I have found no plants connected by roots, with the possible (?) exception of site (4). Most all root systems were very small - not even large enough to leave a hole in the ground. A few plants were big enough to leave a hole, but still I only dug with a cultivator, scooping out soil with my hand.

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

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 false. 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.

In reality, 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 6 years later. I would not suggest using a spade because the roots are pulpy and easily broken. Even the forces created by tilting a spade are sufficient to break the root - leaving you to fish around for what was left. Young plants have a straight tap root. Simply pulling it up will cause the tip to break off. Better to grasp the crown and twist in a circle to loosen the soil first.

For those plants with roots too large to dig up, there is plenty of web advice saying that weekly knocking back of new growth will eventually exhaust the plant. I am finding at sites (4) and (9) that new shoots were originally created and fast growing weekly. But a month later it is mostly just the suggestion of a red bud showing after a week. I am very hopeful this will work. Since the seawall is regularly walked by dozens of 'regulars' this can be continued even if not by me.

Hedge Bindweed (Morning Glory) - all cleared within my territory

There are two types of Bindweed - both in the Morning Glory family. I believe it is Hedge Bindweed, Calystegia sepium, that is in Stanley Park. The arrowhead leaves look similar to the Field Bindweed, except not so pointy at the trailing edge. Like all Morning Glory this plant twines around anything vertical. It prefers sun so I am hoping it will not thrive in the shade of my territory. The extensive root system makes clearing difficult. Any pieces left behind can and will start new plants. You can scratch backwards along the root when it is growing in loose soil. But when growing among other plants, their roots prevent access to the bindweed's roots.

Stanley Park invasive plants - Bindweed Stanley Park invasive plants - Bindweed

Bindweed is spreading mainly from the cultivated gardens on the West side of the park, along the Seawall clockwise. I have found only two small spots within my territory - on the north edge of Hollow Tree park and north of the hydrant on Bridle Path. I have cleared both but return regularly to find one or two new shoots.

Stanley Park invasive plants - sites cleared of Bindweed

In May of 2017 I decided to try to protect what I thought at that time, was perfectly clear seawall going clockwise from Siwash Rock. To make Siwash Rock a 'hard stop' I decided to clear south to the 3rd Beach exit road. This would be the 'no-fly zone'. It would provide a cleared boundary to the huge wild west half of the park. In June, after the higher sun reached the shady north slopes, I found two spots of bindweed already beyond the Rock. I felt there was no choice but to give up the no fly zone idea. IMO the idea of protecting such a huge area of wild, with so little work would be worth the effort, IF those two spots could be cleared. But one would require cutting down and digging up the roots of about 15 - 20 feet of bushes. It would not be difficult for Parks. The real politic is that they will never do it.