The Invasive Race
Puddock Hill Journal #65: There’s more than one race for a backyard steward to worry about.
“The Invasive Race.” How’s that for a loaded headline? But I’m not talking about a race of people—or a race of anything for that matter, if by race we mean a group of individuals with common features.
I’m talking about a race against time—the time it takes the seeds of invasive plants to set.
Darwinian competition is at bottom a contest of reproduction. Under pressure from limiting forces—say, a shortage of nutrients or changing climatic conditions—species that reproduce slowly in small numbers have a disadvantage in relation to those that reproduce fast and prolifically. Humans may be the exception to this rule, but there’s a lot of extinct large fauna to prove the case. The rodents won.
Some invasive plants produce huge numbers of seeds that often germinate early, thus outcompeting slower-seeding natives attempting to occupy the same niche. One of the things that has made garlic mustard so successful as an invader, for example, is its ability to flower even after having been cut down, which is why the preferred chemical-free method of fighting it is to pull it up by the roots.
I don’t have the resources to stub the preponderance of invasives at Puddock Hill, so I am forced to use the string trimmer or, when I need to do so selectively, a hand pruner to cut them as close to the ground as possible. While I’ve been doing this since early spring, the game gets more complicated as native perennials come into their own and invasives hide in their midst.
This week, I waded into the wet meadow, where I noticed some porcelainberry vines had begun to set fruit. Fortunately, that fruit was still far from maturing. I cut and pulled them as best I could, being careful not to kill the native competitors that I hope will continue to compete with them for water and sunlight. And I’ll be back in that meadow many more times in coming weeks.
Angiosperms, which constitute the majority of plants we see, must flower prior to producing seeds—sometimes in a showy manner but more subtly in other cases. Either way, to allow an invasive plant to set seed is to cede the field to its offspring in future years. (Yeah, I guess I made that pun on purpose.)
So when summer arrives, our vigilance should double.
Fighting invasives in high grasses, such as we have in our no-mow areas, is a pretty simple matter of seek and destroy. But among woodlands or meadows of well-established perennials and other herbaceous plants, this becomes more difficult, especially when the invasives are vines (or plants that can behave like vines) such as Asian bittersweet, multiflora rose, mile-a-minute, and porcelainberry.
From a stewardship perspective, one of the hazards of fighting vines with a string trimmer in an area with established plants is that you can take out too many friendly competitors in an effort to get to the bottom of the vine.
When I went out a couple weeks ago to attack a large patch of invasive crownvetch (Securigera varia) that was in full bloom, I soon realized that its low vine habit meant wiping out hordes of well-established goldenrod (Solidago spp.) that I hoped would outcompete it.
The matter was made more challenging by the number of multiflora rose canes that I kept seeing poking their heads above five-foot-tall native goldenrod and Joe Pye weed. In my experience, one can start attacking a multiflora rose cane in one place only to find it originates many feet away. Thus, in most cases, it is a bad idea to chase these invaders with a string trimmer in thick vegetation.
And then there was the porcelainberry, which betrayed its presence by attempting to reach over other herbaceous plants but sent its tendrils from woody runners along the ground that had eluded March brush hogging.
In this case, it dawned on me that I didn’t have the time to do it right. One option would be to go scorched earth with the mower, but, thinking of the pollinators that gorge themselves on late-blooming flowers in that meadow in September, I decided to attack the problem in a more responsible if expensive way. I stopped what I was doing and engaged a couple workers from the lawn service to pick through the barn meadow and extirpate these weeds by hand as best they could, thus preserving the native competition.
I’d love to be able to do this in the wet woods, the big pond embankment, the woods above the big pond, the wet meadow, the east woods—even the tenant meadows that we’ve had to mow this year because the invasives got so bad. But that’s a long list, and I don’t have the resources to comb the entire property digging up bad guys one at a time. The alternative is to pick them off just before they flower or fruit, at least to put a check on the invasive seed bank, and that’s what I’ll have to keep doing.
Meanwhile, Japanese stiltgrass has already started to crop up in patches. Although I sometimes cut it down out of frustration, unless mowed very often it will grow back in no time. Best practice, for those of us who do not spray, is to let it expend its energy all summer and only then cut it back—you guessed it—just before it sets seed.
The stiltgrass is the hare and I am the tortoise. We know who should win that one.
Native blazing star (Liatris spp.) blooms in the patio garden:
Native brown-eyed Susan (Rudbeckia triloba) has cropped up for a second year in the no-mow area behind the garden shed:
I’m glad we planted native tickseed (Coreopsis spp.) this spring in the patio garden:
Coneflower (Echinacea spp.) cultivars naturalize (I hope) in the slope meadow by the house:
Naturalized Old World native Queen Anne’s lace (Daucus carota) grows by the springhouse, looking toward the wet woods:
