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Tuesday, September 29, 2015

It takes a plant community

Sometimes it feels like we’ll never get ahead of opportunistic nonnative plants. Especially with woody plants like Japanese knotweed (Fallopia japonica), it seems once they’re in your garden, you may never see the end of them. 
            In his book Gaia’s Garden, Toby Hemenway argues that opportunistic plants grow where we’ve given them an opening in disturbed ground and will naturally die off as stable plant communities take over (Hemenway prefers the term opportunistic to invasive, which he considers too emotionally loaded. I’m using his terminology). This is a nice idea, but considering how much Japanese knotweed I see in the course of a week’s driving, I wondered how likely Hemenway’s scenario was in my area.
This Japanese knotweed's underground rhizomes could be as much as 60 feet long. It propagates by seeds but is also capable of regenerating from root or stem fragments.
          This week I was pruning dead branches out of a dwarf mugo pine, (Pinus mugo 'Paul's Dwarf') planted eighteen years ago that is now partially shaded by a nearby magnolia. It occurred to me that this could be an example of Hemenway’s point. The branches that were in full shade were dead, with clinging brown needles, whereas the side of the little tree that was still in sun was looking good and producing green needles. I hadn’t shaded out this pine on purpose, I’d just failed to imagine how big the two trees were going to grow and planted them too close together.
Mugo pine reaching for sunlight outside the shade of a taller magnolia

            If the magnolia had cast its shade over an unwanted shrub like Japanese knotweed, I suppose it too would have dwindled. The problem, Hemenway points out, is that suburban landscapes, even our parks, offer so many sunny edges that favor fast-growing plants like the knotweed.
            Of course, shade isn’t the only condition that discourages opportunistic plants. The goal is to replace a plant that you don’t want with one, or ideally some, that you do. If you just remove the offender, you leave open soil for opportunists to take over again. Growing together, a group of native plants that have evolved to cooperate can succeed in grabbing the resources an opportunist needs to survive, not just sunlight but also water, soil nutrients, and room to grow.
            While I wait for my growing collection of native plants to knit themselves into anti-opportunist communities, I’m still cutting a couple of knotweeds at the fence line to the ground every couple of weeks, hoping they’ll eventually run out of stored energy and give up.
I cut it down, but this deceptively frail-looking Japanese knotweed, center, keeps coming back up. Will encroaching smooth Solomon's seal help to curb its growth?



  1. I do have a Japanese knotweed that sends up a sprout a couple times per growing season in my garden. I'd say we're at an impasse. It's not giving up the ghost, but it's also not conspicuously crowding anything else out and (unlike other parts of my garden) I'm able to keep up with it.

    I might get more serious about eliminating it if I hadn't read that it's one of the richest sources of resveratrol -- a phenolic that has some interesting pharmacologic properties. (The jury is still out, as far as I can tell, on whether resveratrol will live up to any of the hype). And more importantly, my friend Helena with Incredible Farm in Todmorden (Yorkshire) calls it her "superfood." She posted last year, "Japanese knotweed....a plant close to my own heart.... This is a highly valuable food plant... The new super food! The Japanese use it a lot.... Generally anything under 8-12 inches is good to use before it goes a bit stringy!" Helena cooks and eats it as you would asparagus.

    Maybe this is a good place to apply a bit of "gardening mindfulness" -- noticing and taking proportionate action based on what's actually going on in your garden (as opposed to what's going on in your head or in other people's gardens as reported in dramatic reports... as seems to have happened here:

    1. Could this be a new mental disorder, fear of invasive plants, emerging in the UK because of superior plant awareness? In the US too we've gotten into a panic about non-native opportunistic plants. Eating them sounds like an ideal response.