The One Big Thing That Makes Invasives Über Villains

Puddock Hill Journal #60: Spring activities remind me why fighting invasive plants is so important.

I ventured to the porch off the library for the first time this year on the first of May. It was a warm afternoon, and the birds were vocal. I espied a pair of Baltimore orioles chasing one another, perhaps in courtship—or defense of courtship. In the course of a minute, besides the orioles, the Merlin app picked up a red-winged blackbird, chipping sparrow, American robin, song sparrow, northern cardinal, red-bellied woodpecker, and warbling vireo.

Birds provide a good reminder of why we backyard stewards do what we do. Earlier in the week, I spotted a green heron on the big pond. A few days later, a pair of wood ducks had joined the annoying Canada geese, who have settled in with a brood of six chicks, so far managing to elude all predators.

While out and about a few days later, one of the dogs started barking incessantly. When I investigated, I found a medium-size snapping turtle attempting without luck to shimmy under the fence:

I thought about attempting to carry the snapper to the gate with a shovel, but he (or more likely she) seemed none too pleased with that maneuver, so I cut a hole from the inside, then went around and pushed her through. When I returned a couple hours later, she had wandered off, no doubt to one of the ponds, where, forgive me, I hope she might do some damage to the geese.

Meanwhile, fish have moved toward the shallows of the big pond, where bluegill nests abound and I also spotted several bass. In a vernal rill in the wet woods, I came upon a green frog. Later, I saw the first butterflies of the season.

These things were a welcome diversion from the main task that has occupied my time since getting back home: fighting invasives. If you’re a regular reader of these posts, you know I’m at war with invasive plants. If you thought I might have defeated them by now, you were sorely mistaken.

I went out into the wet meadow on a hunt for Canada thistle and multiflora rose, but when I hit the upper bank of the small pond, I found a discouraging amount of Japanese honeysuckle (vines mostly but some young shrubs) and mugwort, in addition to more multiflora. After going through several battery recharges and as many yards of string, I had barely made a dent. Jumping to the sloping meadow below the tenant house, I found so much multiflora and thistle that I resolved to have the lawn service mow it for at least a couple of months. As in any war, one must sometimes know when to retreat.

Many invasive plants sprint out in front of slower-growing natives in early spring, which is one of the ways they maintain a competitive advantage. So I tried to tell myself that the natives would come along and assert themselves. And they might—at least more aggressive ones like goldenrod and dogbane and maybe some of the ferns and sedges. On one bank of the small pond where native phlox has performed well the past three years I could see it growing in thick clumps. But for sheer volume it did not hold a candle to the honeysuckle and mugwort.

More than any other trait, what makes invasive plants über villains is their tendency to form monocultures, crowding everything else out. Mugwort is a notorious player in this regard. We have mown patches of it and string trimmed aggressively, but it spreads by runners. On the small pond bank it had not yet formed a carpet—nor had the honeysuckle vine—but both were present every half step, suggesting it will only be a matter of time. My only hope is for the phlox to outcompete them and for the pawpaw trees above to reduce their vigor with shade. Meanwhile, I selectively string trim, meticulously trying to avoid emerging good guys such as Virginia knotweed (not to be confused with highly invasive Japanese knotweed, which thankfully we do not have—*fingers and toes crossed*).

Similarly, the first response of multiflora rose to mowing or string trimming is to spread out like a carpet, consuming everything in its path. Canada thistle also manifests notable vigor, spreading both by seeds and rhizomes.

One rarely sees a single plant of these species—they appear in droves, closing in on nearby vegetation until, if left unchecked, they predominate. That’s what a monoculture is—one thing and nothing else.

Of course, a tendency toward monoculture is not the only characteristic of invasive plants, but it is the one that matters most, as by this trait they crowd out the natives that nourish our native arthropods, which play an important part near the bottom of the food chain, sustaining our ecology.

So, this time of year, our goal is to prevent them from getting a head start on that dominance. Working without chemicals—which I will only use as an absolute last resort—one can selectively string trim, introduce or promote aggressive native plants that might, if you’re very lucky, outcompete them, or, when all else fails, bring out the mower for a year or more. (Canada thistle, I have read, may require mowing for four years to be defeated.)

But I also must remind myself that it’s early days. Even the threat of frost is not quite yet past—technically May 10 in our area. Many of our most competitive natives are just emerging. The hum of my string trimmer may not die down for a long time, but when it pauses I’ll take much satisfaction in birdsong.

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This beautiful flower, star of Bethlehem (Ornithogalum), also turns out to be invasive in the mid-Atlantic and has begun to crop up everywhere here:

Flowers of native pawpaw (Asimina triloba) by the small pond seem otherworldly:

It may be hard to believe, but both of these pictures feature native sassafras (Sassafras albidum) leaves:

Virginia springbeauty (Claytonia virginica) plants flower between the barn meadow and the wet woods:

The old native azalea (Rhododendron spp.) by the barn has started its show:

Seeds hang heavy on a native red maple (Acer rubrum) by the big pond (looking up to the house):