How to Identify Invasive Pond Plants

Written by carol sarao
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How to Identify Invasive Pond Plants
Duckweed can deplete oxygen from your pond's water (duckweed image by Oleg Tarasov from

Invasive pond plants--non-native aquatic plants that spread aggressively--can create a big problem in your water garden or pond. They may be attractive or even beautiful, but invasive plants are pushy intruders that over-compete with native species, deplete oxygen and form floating mats that block sunlight. If your pond has been besieged by invasive plants, you need to determine what they are so you can effectively remove them.

Skill level:

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  1. 1

    Identify the common reed, a perennial grass that grows in shallow water at the edges of lakes, ponds and streams. Note its spear-shaped, light-green blades. If the fluffy flower heads of the grass are blushed with a tint of purple or grey, the grass is likely to be a common reed. Another clue is the reed's towering height; this grass can reach 15 feet tall. Common reeds form dense thickets that block sunlight.

  2. 2

    Distinguish the flowering rush, another invasive perennial grass that grows in shallow water, by looking for pink petals held up in clusters. If the blades are erect and a bright, clear green, the plant is probably a flowering rush. There may be bulblets (new flowering rush plants) forming near the roots. Like the common reed, flowering rush creates dense thickets and can crowd out native plants.

  3. 3

    Recognise Eurasian watermilfoil, an aquatic plant, by noting the dark green, feathery, fern-like leaves growing on long branching stems that can reach 10 feet long. The stems are reddish-brown. Another clue that the plant might be Eurasian watermilfoil is the location, for this plant thrives in sunny parts of the pond.

  4. 4

    Identify duckweed by noting a dense mat of round, tiny, light-green plants that don't exceed 1/8 inch long. According to the Texas A&M University Extension, duckweed depletes oxygen by covering large areas of the pond surface.

  5. 5

    Recognise hydrilla--also called Florida elodea and star vine--by looking for a submerged plant with long, branching stems that have reached the surface and are floating in a dense mat on the top. To further identify the plant, touch the underside of a leaf. If it feels rough, the plant is hydrilla, which has "teeth" on the undersides of the leaves.

  6. 6

    Examine the flower spike to identify purple loosestrife. The blooms, purple with five or six petals, appear from June through August. If the plant is not blooming, look for long leaves with smooth edges arranged opposite one other in pairs.

  7. 7

    Look for bright yellow flowers to identity the yellow iris, also called yellow flag. Examine the flowers to see if they are green-speckled toward the centre. In the absence of flowers, look for sword-shaped leaves standing upright. Yellow iris, a beautiful yet invasive plant, can upset the ecology of your pond by crowing out desirable aquatic plants.

Tips and warnings

  • Wear gloves if you are trying to pull yellow iris by hand, as this plant can cause skin irritation.
  • To avoid introducing invasive plants into your pond, purchase only native plants from reputable nurseries.

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