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 2017 there were only 6 small plants. Two of them had tap roots growing too deep for me to clear. Any regrowth from that depth will probably take a year to surface. The sign posted in July 2017 by ISCMV is bogus. There were no plants still there.
  2. This is a marshy area beside the trail with only speckled sun. 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. This single plant behind the benches, against a tree, also gets only speckled sun. I believe I got all the root.
  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 cutting down new growth, the root will be exhausted.
  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. I am waiting for the summer dry season to allow better access to finish. There are easily a dozen plants. 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.
  7. This spot is just south of the steps. The chemicals have worked on one plant, with another almost dead but still sending up weak shoots. I dug up a new plant about a yard away.
  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 all over it. Only one plant was killed by the chemicals. I dug up the rest, leaving behind root in only one place. I left the hole not filled in so that digging farther will be easy. It is sending up shoots which I will knock back.
  10. I could find no remaining evidence of this spot near the lookout above the gun tower. The chemicals must have worked.
  11. I could find no remaining evidence of this spot near Prospect Point Park. The Blackberries there would out-compete anything else. The signs posted by ISCMV in two places in July 2017 are bogus. There were no plants still there. Hopefully they did not gratuitously spray just to validate the sign.

None of the sites in Stanley Parks' west side would be considered 'extensive'. They are at most multiple individual plant. No plants have been 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 at site (9) were big enough to leave a hole, but still I only dug with a cultivator, scooping out soil with my hand.

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. The ISCMV, during their July 2017 visit, evidently refused my idea to drill holes for chemical injection.

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.