It’s summer, and it’s hot. You look into the pond, and what is there? There are no fish in sight, and the pond is choked with weeds. What are they, and how did they get there? Help identify the small weeds that are taking over the pond.
What is a Weed?
A weed is simply an unwanted plant. Weeds tend to grow vigorously, taking over places where other plants could grow. If you want water lilies and you have algae, the algae is a weed. Weed plants are tough and have the ability to grow just about anywhere.
Why Control Weeds?
Weeds can change an ecosystem, whether it is a small pond or a forest or the side of a road. They can make it hard for other animals and plants to grow. This means that weed control is important, whether it is in an aquatic or terrestrial environment. Know what your weeds are and how to control them.
Types of Small Pond Weeds
While you might think that large pond weeds would be more aggressive and able to take over a pond ecosystem, small weeds can easily take over the pond. Controlling these small weeds can be challenging. Chemical applications tend to wash off and damage the entire ecosystem of a pond, including fish, birds, and invertebrates. It can be tricky to collect small pond weeds with a pond net, since many will escape and continue to reproduce rapidly.
Many pond weeds dislike moving water, so adding a waterfall or stream to a pond is one way to control small pond weeds. A pond skimmer and a good pond filter will also help control weeds once they have entered the pond.
Algae: A Weed in the Water Column
Algae can be present in the water or on top of the water. In the water, it makes the pond look murky and looks like suspended sediment. On top of the water, it looks like green or brown sheets or strings and it can be difficult to capture. However, when algae dies, the process of decomposition makes it hard for plants and fish to survive in the pond, because the algal decomposition uses up precious oxygen.
Algae loves heat. Control the temperature of the pond by planting trees and creating a shadier environment. Algae also likes still water. Help the water move with a solar-powered waterfall or pond bubbler. This will also add oxygen to the pond. Get a good quality pond filter to capture some of the algae and collect the algae by hand with a pond net if the problem is severe.
Watermeal is a Tiny Pond Weed That Forms Mats
Watermeal (Wolffia spp) does not look like a threat. The plant looks like a tiny ground-up green meal. It does not have roots and hundreds of plants can sit on the tip of your finger. While it does not look like a danger to pond life, its small size means that watermeal can easily float on top of or in a water body, causing oxygen depletion and the death of submerged plants. A pond skimmer is a good choice for controlling watermeal.
Duckweed: The Small Floating Pond Weed
Both the common duckweed (Lemna minor) and giant duckweed (Spiroldela polyrhiza) are small floating plants that sit in large mats on the surface of the water. Ducks eat duckweed and move it from pond to pond. Gardeners may unintentionally introduce these tiny plants into the pond with other aquatic species from the nursery. Duckweed looks innocuous: many duckweed plants can fit on the tip of your finger, since they often reach only 1/8 of an inch in width at their largest. However, large mats of duckweed need to be broken up and scooped out of the pond, or they will prevent light and oxygen from entering the pond.
Mosquito Fern: A Small, Fern-Like Pond Weed
Mosquito fern (Azolla caroliniana) is a delicate, tiny, fern-like plant that floats on the surface of the water. Underneath the water, a single root hangs down. The fern-like plants range from green to red and are quite small, from ½ an inch to 1 inch in length. Like duckweed, the mosquito fern can form a thick mat on the surface of the pond that prevents the entrance of light and oxygen. The mosquito fern should be scooped from the pond if a mat begins to form.
In the spring and summer, watch the pond carefully for signs of small weeds before they become a big problem. Create a pond environment with moving water and shade to discourage weeds and make sure that you remove the weeds with a net, skimmer, or filter so that you do not need to turn to other weed control options.
Tricia Edgar - Tricia Edgar is a gardener, environmental educator, and science writer from the Pacific Northwest.
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