Pretty Intruders: Water Hyacinth and Other Invasive Flowering Pond Weeds


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Purple loosestrife is beautiful, but it crowds out native species. Photo: Muffet / CC by 2.0

What’s that plant flowering in the pond? It seems so healthy and abundant, yet you can’t remember planting it there. Gradually, the plant seems to sprout up everywhere around the pond, and you realize that it is an invasive flowering weed. These plants may be sold in nurseries, but they can easily take over the home garden and may spread into adjoining wetland areas as well, crowding out native species that support local animals and maintain native ecosystems.

Water Hyacinth is a Pretty Purple Pond Invader

Water hyacinth (Eichhornia crassipes) is a beautiful weed that has become naturalized in much of the southern United States. It is originally from South America. Water hyacinth has lavender flowers on a long stalk. The plant can grow to be 3 feet tall, and it has dark green leaves and a thick, branched root system under the water. This makes it difficult to remove water hyacinth. In a large pond, it is quite possible for the leaves of the water hyacinth to cover the entire surface of the water. Cold water, salty water, and fast-moving water are all unpleasant environments for the water hyacinth, but a slow warm pond is a perfect home for this pretty invader.

Purple Loosestrife Spreads With Roots and Seeds

Purple Loosestrife (Lythrum salicaria) is a very invasive weed throughout much of North America. It originated in Europe and came to North American in the 1800s. From a distance, purple loosestrife is beautiful. It has somewhat heart-shaped leaves and has bright purple flowers on a spike, similar to foxgloves (Digitalis spp). Unfortunately, loosestrife is excellent at reproducing, and each plant will create millions of seeds every year. The seeds are tiny and spread on the wind and water, while the roots of the plant create a mat that prevents other plants from growing. Hand-digging or cutting the flowers of the plants in the summer before they set seed is one way to control purple loosestrife, but if you do this, bag the plants well so the the seed does not spread to other areas.

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