Pond owners often face the frustration of dense green growth, commonly referred to as “pond grass.” This nuisance growth is typically not true grass but rather a collection of algae and vascular aquatic plants that flourish in warm, nutrient-rich water. Effective management requires a strategic approach, starting with correctly identifying the type of growth and then employing targeted physical, chemical, and preventative measures. Addressing the immediate symptom is necessary, but long-term success depends on managing the underlying environmental conditions that fuel this excessive vegetation.
Identifying the Types of Aquatic Vegetation
Successful treatment begins with accurate identification, as different types of aquatic growth require distinct control methods. The vegetation causing problems usually falls into three main categories based on where they grow in the water column. Filamentous algae, often described as “pond scum,” forms slimy, hair-like mats that frequently float on the surface. Submerged weeds are rooted plants, such as coontail or various pondweeds, that grow almost entirely below the water surface. Emergent weeds, like cattails and rushes, are rooted near the shoreline but have stiff stems and leaves extending above the water.
Physical Removal Techniques
Physically removing the nuisance growth offers an immediate, non-chemical way to restore the pond’s usability. Manual methods like using specialized aquatic rakes or V-shaped cutters can effectively pull or slice through submerged and floating mats of vegetation. For large-scale infestations, mechanical harvesters or hydro-rakes can be deployed to cut and collect large volumes of biomass.
Removing the plant material from the pond is mandatory. If the cut vegetation is left to decay, it releases its stored nutrients, primarily phosphorus and nitrogen, back into the aquatic system. This recycling of nutrients fuels the growth of future algae and weeds. The collected biomass should be disposed of on dry land, away from the pond’s edge, often used as compost.
Using Approved Aquatic Herbicides
Chemical control provides a fast and effective option, but it requires careful application of specific, approved products. Aquatic chemical treatments are divided into algaecides, which target algae, and herbicides, which target vascular plants. These chemicals must be certified by the Environmental Protection Agency (EPA) for aquatic use to ensure they do not pose unacceptable risks to fish or other non-target organisms.
Contact vs. Systemic Herbicides
Herbicides are categorized based on how they affect the plant: contact or systemic. Contact herbicides, such as Diquat, kill only the plant tissue they touch and are fast-acting, typically effective for annual weeds or surface-level algae. Systemic herbicides, like Fluridone, are absorbed by the plant and translocate throughout its system to kill the entire structure, including the roots. Systemic treatments are suitable for perennial weeds but require a longer exposure time, often 45 to 90 days.
Safety and Application
A safety consideration when using chemicals is the risk of dissolved oxygen (DO) depletion. When a large volume of vegetation is killed quickly, the subsequent decomposition consumes significant amounts of DO, potentially leading to fish kills. To mitigate this risk, treat only small sections of the pond (one-third to one-half) at a time, allowing a 10-to-14-day interval between applications. Local regulations often require special permits for applying aquatic herbicides, so checking with local authorities is necessary before application.
Long-Term Nutrient Management and Prevention
The most sustainable method for controlling aquatic growth involves addressing the underlying cause: an excess of phosphorus and nitrogen in the water. This nutrient overload, known as eutrophication, results from runoff carrying lawn fertilizers, pet waste, and soil sediment from the surrounding watershed. Reducing the inflow of these nutrients is the ultimate goal for long-term health and clarity.
Preventative Strategies
Installing a submersed aeration system introduces dissolved oxygen to the lower water layers. This helps oxidize organic matter and binds phosphorus into forms unavailable for plant uptake. Another approach is using pond dyes, typically blue or black, which block the penetration of sunlight necessary for photosynthesis in submerged plants and algae.
Controlling Runoff
Establishing a vegetative buffer zone around the pond’s perimeter effectively filters incoming runoff. This zone of un-mowed, native plants slows stormwater flow, allowing sediment to settle out while roots absorb excess nutrients. Discontinuing the use of phosphorus-containing fertilizers within at least 20 feet of the shoreline can significantly reduce nutrient loading. This combination of aeration, light blockage, and runoff control creates an environment less hospitable to nuisance growth, resulting in a healthier pond ecosystem.