Dealing with Weeds in 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:

• 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.

• Hydrilla – An invasive weed with long stems and whorls of pointed leaves. It grows rapidly and spreads through fragmentation.

• Eurasian Watermilfoil – Feathery leaves arranged in whorls along the stem. Spreads aggressively through fragmentation. Forms thick underwater mats

• Tapegrass – Long ribbon-like leaves that grow in dense stands.

• 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:

• Duckweed – Tiny green floating plants that quickly cover the surface of still water.

• Watermeal – The smallest flowering plant. Forms a powdery green layer on the water’s surface.

• 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:

• Cattails – Tall plants with strappy leaves and distinctive seed heads. Have extensive root systems.

• Bulrushes – Tall grass-like plants growing in dense stands in shallow water.

• Pickerelweed – Produces spikes of blue flowers. Spreads aggressively in shallow areas.

• 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:

• Planktonic algae – Microscopic, suspended algae that causes green, cloudy water.

• 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.