Roots and Shoots: Aquatic Superpowers

Between the time I wrote the first draft of this column and my deadline a few days later, I counted another 23 plants in the pond, in addition to the 30 already there. Several yards away, below a thin pane of ice, shone the pops of chartreuse foliage. 

Watercress grew and spread quickly in my pond during winter. Photo by P. Doan

Watercress grew and spread quickly in my pond during winter. (Photo by P. Doan)

I noticed the first plants shortly after the New Year and used my plant app, Picture This, to ID them as watercress (Nasturtium officinale). Maybe it was swept downstream during the heavy storm over the holidays when the pond flooded a dam built on the stream by a previous owner. Or maybe the seeds had been in the pond floor and the heavy flow moved them enough to germinate. It’s probably here because someone planted it upstream. 

Watercress is a popular, peppery-flavored green that is harvested and sold and foraged because it can grow in many settings. Native to Europe and parts of Asia and Africa, in the U.S. it’s considered by the Forest Service to be “invasive and noxious” in 46 states, including New York. 

Clearly, watercress is a hardy plant. While temperatures have been mild this winter, germination information on retail sites that sell seeds list it as needing a temperature of at least 45 degrees. Generally, I’ve found that shallow streams like this one follow surface air temperatures, rising and falling within hours, or a day. The plant wasn’t getting much insulation from its aquatic habitat, but here it is! Some of the plants have grown tall enough in a month to rise above the water. 

While watercress is considered an invasive in New York, seeds are widely available. The plant is sought after by gardeners and foragers for its high nutrient value. 

Watercress is a Tier 3 invasive species, meaning the New York Natural Heritage Program, a conservation agency, has found it to be a “highly invasive species in medium abundance with a management goal of containment.” The system has four tiers (Tier 3 is one below the severest) and Abby Bezrutczyk, conservation area manager of the Long Island Invasive Species Management Area, clarified that watercress is being monitered and encouraged me to submit it to iMapInvasives, which I had already done.

“Its ecological impacts aren’t fully known and documented, aside from taking up nutrients and somewhat altering stream flow if it grows in a larger mat,” she said. “That’s part of the reason it’s classified as having a moderate ecological impact in New York.”

Watercress is a significant issue on Long Island but not as much in the rest of the state. When I discussed my pond with Sam Beck-Andersen, a director of invasive species programs in the Finger Lakes region, he said: “Hand-pulling is a good method for controlling it at this stage. Leaving it allows more opportunity for it to fragment and continue downstream.” Watercress spreads by seed and parts of the plant can root and grow, too. 

I could harvest it but after reading about the possibilities for ingesting liver fluke and Giardia, parasites that can live on the plant, I am going with a hard “no.” When I initially tried to track down information about watercress, most of the sites I found were about foraging. As with any free salad found in a waterway, eat at your own risk. 

Gardeners can plant watercress in containers and keep it out of waterways, where it can grow into 10-foot mats, disrupt the ecology of the pond or stream and continue downstream. In this stream, the water flows into Trout Creek, then Wiccopee Creek and Fishkill Creek, a 34-mile tributary of the Hudson River. That’s a lot of potential watercress habitat. 

My pond is primarily a frog habitat. I love to watch the cloudy balloon egg sacs become tadpoles and listen to the chirps and croaking. I’m not eager to see what impact the watercress will have on them but I might not have a choice. This will be a work-in-progress that will have to wait for warmer days. If you’ve got a wet suit and a will to pull weeds, I could use the help.

Leave a Reply

The Current welcomes comments on its coverage and local issues. All online comments are moderated, must include your full name and may appear in print. See our guidelines here.