How to Kill Problem Watercress

Watercress is tasty but invasive.

Nutritionists and health-conscious consumers endlessly extol the virtues of watercress as a healthy, low-calorie vegetable. They encourage planting it in the garden as an inexpensive home-grown staple. But what many often neglect to mention is that watercress can be a problematic, invasive weed. They grow year-round, and cutting them back only makes them grow more thickly. To get rid of watercress for good, you must get to the root of the problem.

Things You'll Need

• Trowel

Instructions

1. Dig the watercress up before it flowers. Remove as much of their root system as possible. If you can manage to temporarily drain or block their access to water, it will make digging easier.

2. Remove the dug watercress from the area. If left in place it will re-root.

3. Keep digging any watercress that re-sprouts. Watercress puts down a lot of seed. Those already in the soil will begin to germinate once the larger plants are gone. Keep pulling the young plants out roots and all and the patch will dwindle and eventually disappear.

4. Change the water flow if possible. Watercress grows best in low, flowing water. Damming small creeks to keep the watercress' foliage flooded will inhibit its ability to grow back. Drying out the soil beneath the watercress will eventually kill any remaining plants.

5. Block the watercress's access to sunlight. A temporary shade of two-by-four legs and a wire mesh roof with a cardboard layer to block out the sunlight will do the trick until the watercress no longer grows back. Or, for a more permanent solution, plant water-loving trees with thick canopies near the infested site.

Tips & Warnings

• As an alternative to digging, treat your watercress with a broad-spectrum herbicide. However, you run a serious risk of polluting the water supply. The International Commission on Irrigation and Drainage recommends using herbicides that contain 2-4,D or glyphosate. Instead of spraying the herbicide on, dip a paintbrush in the herbicide and paint it directly on the leaves to avoid contaminating the water. April, May and June are the best months to apply herbicide. However, the herbicide will not control the seed already in the soil.

References

• University of Florida; Watercress; James M. Stephens; 2009
• University of Hawai'i at Manoa; Predicting Watercress Yield; Kent Kobayashi et al.;
• Utah State University; Watercress in the Garden; Trudy Kendrick et al.; February 2008
• International Commission on Irrigation and Drainage; Aquatic Weeds & Their Management; March 2002