Pond weeds are a common problem in large natural ponds. As ponds get older, they tend to fill up with nutrients (eutrophication) and sludge, which makes plants and algae grow too much. Each year, the overall growth of both beneficial and unwanted plants increases and can eventually become a problem. Too much plant or algae growth is not only unsightly, but it can also slow down the flow of water and make it hard to swim or use the pond for fun.
The first step to solving the problem of unwanted pond weeds is to identify the weed or plant. We have broken the most common pond weeds into 3 categories:
Pond Maintenance Services and products made just for big ponds are available if you need help with your pond.
Having a pond on your property can be a beautiful addition that provides habitat for wildlife However, ponds frequently become overrun with nuisance weeds There are various types of pond weeds, and it’s important to properly identify them in order to determine the best control method. With a bit of diligent maintenance, you can keep pond weeds under control and maintain the aesthetic and functional value of your pond.
Common Types of Pond Weeds
There are three main categories of pond weeds: submerged, floating, and emergent. Each has their own characteristics and growth habits.
Submerged Weeds
Submerged weeds grow under the water, either rooted to the bottom or unrooted. Common submerged pond weeds include:
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Pondweeds – A group of plants with long slender leaves growing along the stems They are rooted to the bottom with branching stems that can reach the surface.
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Hydrilla – An invasive weed with long stems and whorls of pointed leaves. It grows rapidly and spreads through fragmentation.
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Eurasian Watermilfoil – Feathery leaves arranged in whorls along the stem. Spreads aggressively through fragmentation. Forms thick underwater mats
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Tapegrass – Long ribbon-like leaves that grow in dense stands.
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Coontail – Unrooted, dark green plant with whorled, forked leaves. Often tangled into mats.
Floating Weeds
Floating weeds have leaves and flowers that float on the water’s surface, but are rooted to the bottom. Examples include:
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Duckweed – Tiny green floating plants that quickly cover the surface of still water.
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Watermeal – The smallest flowering plant. Forms a powdery green layer on the water’s surface.
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Water Hyacinth – Showy lavender flowers with bulbous leaf stalks. Spreads rapidly and can form dense mats.
Emergent Weeds
Emergent weeds are rooted in the shallows and have stems and leaves extending above water. Common emergent weeds include:
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Cattails – Tall plants with strappy leaves and distinctive seed heads. Have extensive root systems.
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Bulrushes – Tall grass-like plants growing in dense stands in shallow water.
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Pickerelweed – Produces spikes of blue flowers. Spreads aggressively in shallow areas.
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Yellow Iris – Yellow flowering plants spreading by rhizomes and seeds.
Algae Growth
Algae, though not a true aquatic weed, can proliferate in ponds. There are two main types:
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Planktonic algae – Microscopic, suspended algae that causes green, cloudy water.
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Filamentous algae – Long strands that form dense mats floating at the surface.
Excess nutrients, sunlight, and warm temperatures can cause excessive algae growth.
Impacts of Pond Weeds
Weeds and algae can negatively impact ponds in various ways:
- Crowd out desirable native plants
- Reduce biodiversity
- Spread aggressively and cover the entire pond surface
- Deplete oxygen levels when decaying
- Reduce water flow
- Entangle boat propellers
- Look unsightly and impair recreational uses
If pond weeds are taking over your pond, action should be taken to control and manage growth.
Controlling Pond Weed Growth
There are several methods to manage nuisance weeds and algae in ponds:
Manual Removal
Manually removing weeds by hand pulling or raking can be effective for small infestations. Remove as much of the roots as possible. Be sure to dispose of plant material out of the water to prevent re-growth. Manual removal works best on emergent shoreline weeds.
Mechanical Removal
Mechanical cutting, harvesting, or dredging removes large amounts of plant material. Harvesters are boats with cutting blades to mow vegetation. Dredging removes rooted plants by scooping them from the pond bottom.
Biological Control
Introducing herbivorous fish, insects, or plants helps reduce weeds naturally. Grass carp eat a variety of submerged plants. Weevils eat invasive watermilfoil. Barley straw inhibits algae growth. Introduce species carefully to avoid unintended harm.
Artificial Shading
Shading ponds with dyes or surface covers blocks sunlight to suppress plant and algae growth. Light restriction inhibits photosynthesis and growth. Make sure oxygen levels stay adequate.
Herbicides and Algaecides
Applying EPA-approved aquatic herbicides kills weeds or algae. Systemic herbicides kill the entire plant. Contact herbicides kill only the parts sprayed. Granular forms sink to kill roots. Carefully follow all label instructions for best results.
Nutrient Control
Reducing nutrient inputs through runoff management or treatment decreases growth of weeds and algae. Diverting sources of fertilizer runoff limits nitrogen and phosphorus entering the pond. Additives bind phosphorus making it unavailable. Barley straw releases algicidal compounds.
Integrated Weed Management
The most effective approach is to use multiple strategies as part of an integrated weed management plan. Combine manual removal for small infestations with herbicide application for larger growths. Use mechanical harvesting for robust vegetation along with algicides for algae control. Reduce nutrient inputs and establish native plants to outcompete weeds.
Weeds can quickly get out of control if left unmanaged in ponds. A variety of aquatic weeds and algae occur in ponds, each requiring specific control methods. Understanding the types of weeds present and implementing multiple management strategies gives the best results. A thoughtful integrated weed management plan will keep ponds healthy, improving aesthetics and usability. With routine maintenance and observation, pond owners can stay on top of nuisance vegetation and maintain the full benefits their ponds provide.
Shoreline / Emergent Pond Weeds & Plants
Emergent / Shoreline plants are one of the most common problem in ponds. Grass, irises, phragmites, cattails, and bullrushes can grow quickly in ponds with shallow shorelines (up to 2 feet deep). Often, these plants initially colonise new ponds by seeds carried by wind, birds or other animals. Once established, many marginal plants can spread rapidly underground making them difficult to control.
Yellow iris are a non-native plant originally introduced from Europe. They can get up to 4 feet tall, have a lot of bright yellow flowers in the spring, and have roots that are made of fibers. They don’t spread too quickly through their root system, however they can easily spread by seed. They grow in shallow water up to about 12″ deep.
Cattails are a native plant that grow up to 6′ tall. As a result, they can easily spread to new ponds by seed because they grow in ditches and other wet places. In shallow ponds, they quickly overtake the shoreline and have extensive root systems that are difficult to remove.
Pickerel weed is a native plant with blue-violet flowers. They that grows in a variety of conditions, from moist soil, up to water 3′ deep. They are great places for young fish to grow, but they spread quickly and can block the edge of ponds if you don’t stop them.
Bulrush are common along shorelines in ponds, marshes, wet ditches and lakes. There are several native species of bulrush, ranging in size from 2′ to 8′ tall. They prefer moist soil up to depths of 2′. Bulrush don’t grow very fast and don’t usually take over the shore, but cutting back their roots on a regular basis can help keep them neat and in check.
Also known as Phragmites, is an invasive plant that grows and spreads rapidly. It grows in big, dense colonies that can take over misty places like ditches and shorelines and beat out native plants. The common reed grows in wet soil up to three feet deep and can get up to fifteen feet tall. In the late summer, it makes a feathery seed head.
This plant is native to the area and grows in wet soil and water that is only about 15 cm deep. It is also edible and is high in vitamins A, C and E. It produces clusters of small white flowers in summer, and can spread quickly by seed. There are several different species of Water Plantain found in Canada.
Submerged Pond Weeds & Plants
Although beneficial for ponds, submerged pond plants aren’t considered usually considered very pleasing to the eye. In fact most people refer to them as sea weed, pond weed or some other unflattering name.
Coontail, also known as hornwort, is a dark green, branching aquatic plant that grows submerged in the water. Although it does not have true roots, it does anchor itself to the sediment. In nutrient rich ponds, coontail can grow very rapidly and become a nuisance.
Native to North America, Elodea has small bright green leaves that grow on branching stems. It begins growing very early in the spring in cool water and can be invasive in certain conditions.
Curly-leaf pondweed is an species that was introduced from Eurasia. It is fast growing plant and can grow very quickly, overtaking other pond plants.
Eurasian water-milfoil is a invasive, fast-growing perennial, that will form dense underwater mats. It typical grows shallow water one to three metres deep, but can also root much deeper. The fall and winter are when a lot of the season’s growth dies off, which leads to more sludge and less oxygen.
Tape Grass, also known as Eelgrass or Wild Celery, grows in shallow water. Its long, narrow leaves grow from a group at the plant’s base. the leaves grow up to 1 meter long and are only about one centimeter wide. When the water warms up in the summer, tape grass starts to grow quickly. It will split by sending out runners from the base.
Its plant name is S. pectinatus, and it grows in shallow water. Its roots form thick mats on the bottom of the pond. It has long branching stems and very narrow leaves that taper to a point. It can be fast growing in the right conditions. At first glance, it can be confused with Curly-Leaf Pond Weed.
Chara, which is also called Muskweed, is an algae that looks like a plant that is submerged. It is often mistaken for coontail because of this. It is a large, bright green branching algae that has no roots and also has a distinctive odour. When pulled from the water it has a noticeable garlic-like smell. Chara will form dense mats that can cover large areas if left alone.
Nostoc (also known as Freshwater Grapes) is actually an algae that resembles green grapes. They are often confused with frog or toad eggs when they are smaller. At certain times of the year it can also look completely different, resembling thick green jelly. Nostoc is not does not usually grow in abundance in most ponds causing any real problems.
How to Get Rid of Weeds in Ponds & Lakes: Aquatic Weed Control Tips
FAQ
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