When I was 10 years old living in the southeast corner of Missouri, I learned the fine art of picking up a hoe, the trade of chopping cotton and soybeans and the definition of a weed.
My father would drive down the turn row and ask if I saw any plants that were not cotton. I’d reply that I saw maybe 10. He would reply, “Well, that’s 10 too many!” Our banker who gave us the crop loan would drive by to see if we were living up to our side of the bargain and keeping the unwanted plants (or weeds) down so that the cotton could get the maximum benefit of nutrients.
Fortunately, the days of getting to the field at 6 a.m. to chop down anything that was not cotton are long gone. But every year, reports of nuisance outbreaks occur because an enthusiast wants to rid their pond plant population by dumping unwanted plant material into canals or bodies of water, where the growing environment is conducive for rampant, unchecked growth. Total eradication of some plants is nearly impossible once they have started growing.
Prevention & Containment
Above all, think prevention and containment. Consider aggressive plant species like a sunburn. The easiest way to avoid the hassle is to stay indoors and prevent the sunburn altogether. Once you have a sunburn, all you can do is contain what you have and not making the burn any worse. Many of these plants are considered invasive because they are difficult to eradicate and can thrive in contaminated environments. Excess nutrients and fertilizer runoff spill into local waterways, causing the water to become nutrient-rich environments for certain species of invasive plants, while contaminating the water for other plant and animal growth.
Plants to Keep in Check
Hydrilla verticillata is a submerged plant that can be as much of a problem as nut sedge is in your lawn. It is a plant that can grow in water just a few inches deep, all the way down to 30 feet deep. The leaf has a saw-tooth edge, and the underside is rough, unlike other submerged oxygenators such as elodea or anacharis. It was introduced as an aquarium plant in Florida during the 1960s. One particular batch was deemed unsatisfactory and dumped into a canal, where it rapidly flourished. This plant can tolerate freezing-cold temperature as well as lake drawdowns. It grows aggressively, even choking out other species of plants by reducing the oxygen and nutrient levels. It is spread by fragmented pieces drifting into other bodies of water. It has been found as far south as Texas and as far north as Canada.
Cattails are aggressive plants that multiply by rapidly growing rhizomes and seed. There are two main varieties: Typha latifolia, the broad-leaf variety, and Typha angustifolia, the narrow-leaf variety. They grow in shallow bodies of water generally 1 1/2 feet or less in depth. These plants can grow from 3 to 10 feet quickly. It is common to see them take over entire streams and ponds. They can be found from the bays of the Great Lakes down to Texas.
Water canna (Canna flaccida) is known for its large, flat, green leaves that unfurl from long stems, which typically grow between 6 to 9 feet tall. They are topped by large, brightly colored red, orange and yellow flowers. It multiplies by rapidly growing perennial rhizomes. It grows submerged in muddy or sandy areas that protect the rhizomes from freezing-cold air temperatures.
Water lettuce (Pistia stratiotes) is a floating plant that is composed of thick, green leaves that grow in a rosette shape around long, white roots that are submerged under the water surface. They reproduce asexually, which means the plant quickly makes multiples of itself by sprouting several daughter plants that are connected by short stems called stolons. Once the stolon is cut, the daughter plant becomes a new, independent plant that produces several daughter plants of its own, and so on. These are highly aggressive plants that can easily overtake a lake or stream within months! This nuisance species thrives on water contaminated with sewage and fertilizers and eventually strangles out other plant and animal life by blocking sunlight, causing oxygen and nutrient depletion. If all that wasn’t enough, they are known havens for mosquitoes and mosquito larvae.
Umbrella palm (Cyperus alternifolius) has long, thick stems that can grow up to 8 feet tall. They are topped with a tuft of leaves that look like umbrellas. This plant has survived many winters in Arkansas while continuing to proliferate. Our garden center planted a single gallon of this plant, and seven years later, it had to be removed from our pond with a forklift. The original pot had disappeared, while the plant seemed to free-float in water. This one plant weighed more than 1 ton when it was removed.
Water clover (Marsilea mutica) resembles a four-leaf clover, but this invasive species is actually a fern. This plant grows thick tufts of clover that thrive in boggy, muddy and sandy areas. It multiplies by producing spores and spreading its thick vegetation across an area. They are aggressive growers that will overtake other plant life by smothering them out.
The lotus, or Nelumbo, is a favorite of many pond keepers, with its lovely, large foliage and colorful blooms. Left unchecked, this plant can rapidly grow and take over an entire pond. We regularly use this plant, but we keep it in check in a large plastic or net pot.
Most waterlilies today are hybridized varieties, such as the wild waterlily (Nymphaea odorata). These varieties generally remain in check because they reproduce asexually. Wild seeds from the bloom of the Nymphaea odorata are viable. Considering that the plant will have one to two blooms per week with seeds, it can shortly overtake any waterway.
The yellow flag iris (Iris pseudacorus) has long, thin, flexible leaves that stand tall above the water level, resembling an ornamental grass. It has bright-yellow, three-petal blooms. These aggressive plants multiply by rapidly growing rhizomes and dispersing them into the surrounding environment. It can easily overgrow a waterway within months.
Lizard’s tail (Saururus cernuus) grows long, red stems covered in large, green leaves that can reach up to 4 feet tall. It produces a soft, white bloom that is long and curved, resembling an animal’s tail. They are native to North America and can thrive in shallow or deep waters.
Evergreen water celery (Oenanthe javanica) is one of the few water plants that is prolific even in the winter. It can grow quickly enough to choke any waterway if not controlled. Fortunately, the plant is a favorite of koi. It can grow in our area at a rate of up to 2 feet per week!
Horsetail reed (Equisetum hyemale) grows long, green, vertical, hollow stems with rough, black bands about every 2 inches, indicating the joint. They multiply by producing spores and creating long runners underneath the soil that can grow under or around concreted areas, producing new stalks as it goes. It can thrive in small spaces and is very popular in Asian-inspired designs. This plant can withstand most winters and has been found across North America.
Parrot’s feather (Myriophyllum aquaticum) grows long vines that are covered in tiny, green, feather-like leaves. It can grow up to 2 feet above the water level and will spread as far as it can. It has been known to smother out other plant life by blocking sunlight and causing oxygen and nutrient depletion in waterways. It can also clog up streams and other waterways with its dense foliage. They multiply from its perennial rhizome or from segments of the plant that have been cut off, so trimming the plant back will actually cause new plant growth. It tolerates most herbicides and thrives in nutrient-rich, warm water. This plant is most often found in the southern United States, but it has been found as far north as Massachusetts.
Pickerel rush (Pontederia cordata) has long, green stems surrounded by green, shiny leaves that reach up to 6 feet tall. It produces a cone flower that has many small, purple blooms. They multiply by perennial rhizomes and seeds dispersed into the surrounding environment. This plant can thrive in unfavorable environments where other aquatic plants cannot.
Water poppy (Hydrocleys nymphoides) has shiny, green leaves that rest upon the water surface, along with soft-yellow blooms. It grows aggressively in warm, wet climates and can overgrow the water surface within months. They multiply in fragments, starting new plant growth. They are found in the southern parts of the United States.
The important thing to remember is that invasive species are easily controlled if you follow these two steps: prevention and containment. If you can prevent the plant growth in the first place, there won’t be any need to control overgrowth or seed and spore dispersal.
But if you’re like me and enjoy these beautiful species, the other step is containment. Place your invasive plant species into pots or containers, and that will create a physical barrier between the plant’s reproductive rhizome or runners and the surrounding environment. If you plant these species into your soil, gravel, bog or other warm, wet environment, they will grow unchecked and can overtake the surrounding waterway within months. Also, once many of these species have established their rhizomes or root systems, they are nearly impossible to contain, since the rhizome is protected from surface temperatures and herbicides. Others have seeds or spores that can remain dormant until the ideal growing environment is achieved, and then they begin new growth without the aid of humans. As long as the invasive plant species are properly contained and managed, they make a beautiful addition to any water feature that will last for years to come.