Weeds in your pond can harm the fish and other aquatic animals by disrupting the balance between nutrients and oxygen. Weeds can develop in and around the pond; some are beneficial as they feed fish and filter water, while others are problematic. Three types of pond weeds are submerged, emergent, and floating.
Submerged weeds have a portion of the plant and root system visible above water. They include bladderwort, American pondweed and curly-leaf pondweed. Emergent weeds, such as alligator weed, are strong and have stiff stems. Floating weeds have leaves visible above the surface and roots reaching the pond’s bottom. They include algae, water hyacinth, and watermeal. You can control pond weeds using the following methods that will protect aquatic life:
Manual removal
Cutting or pulling up weeds is a fish-friendly technique for your garden pond. Pull up weeds with a weed puller or rake and then move them away from the pond, so they do not end up in the water later.
This is effective for controlling emergent weeds that reproduce through rhizomes. Manual removal is best done around July, August, or September when the weeds lack the energy to resprout. You will have to repeat this process yearly until your pond is entirely clear of weeds.
Cut off or pull weeds during their early stages of growth. American Pondweed can be eradicated by cutting and raking, although there is a possibility that they will resprout from the roots and seeds.
You can also cut, rake and vacuum string algae from your pond. They have soft stems, which make it easy to remove them by hand. Dead decaying plants can decrease the oxygen in water, which could potentially harm your fish. Therefore, when disposing of dead plant matter, you must take care to avoid regrowth from cuttings.
This method is cheap but labor-intensive. Always wear gloves when picking weeds, as some plants may cut your hands. You can also use pond weed cutters which are light enough to handle but can sink to the bottom and cut pond weeds at the roots.
UV sterilizer
You can break up and remove free swimming algae by using UV sterilizers. UV clarifiers are suitable for use at a smaller scale and are harmless for fish and other aquatic wildlife. This method is effective against duckweed and watermeal. You can place the sterilizer above the pond and use it for a long time.
Fish-friendly herbicides
Some chemical herbicides provide effective weed control without harming your pond fish. These herbicides are specifically manufactured to eliminate specific algae and duckweed types. The manufacturer indicates suitable dosage amounts to kill the weeds and protect the fish.
Fluridone is a broad-spectrum herbicide absorbed by weeds, killing them. It is slow acting, taking approximately one to three months to remove weeds. The pond water can be used for irrigation and supporting fish as the chemical is safe.
Copper sulfate or blue stone is inexpensive, readily available, and used for algae treatments. Water treated with copper is safe for fishing, swimming, irrigation, and watering livestock. Before applying copper compounds, examine your pond water’s alkalinity levels. Copper can be toxic to fish when used in acidic waters.
When you use herbicides, it is best to remove dead weeds before the rainy season. Rainwater can dilute any remaining weed killers into the groundwater. Stick to the manufacturer’s instructions when using herbicides for maximum efficiency.
Pond dyes and shading
This approach is impactful in dealing with algae. Pond dyes limit the sunlight available to the algae, helping control its spread. However, this method will negatively affect other plants in the pond that require sunlight. Root systems will be stunted due to the lack of light.
Algae-eating fish
You can put fish in your pond that can feed on algae and other tasty weeds. Algae eaters include shrimp, catfish, and snails. They will feed on pondweeds while still young and help you manage weeds. Koi, goldfish, and grass carp will feed on water lilies and water hyacinth. Using fish for weed control is only effective if the pond is not overgrown.
Drain your pond
Draining the pond is an alternative to manual and chemical weed control measures. This method is best used for dealing with green water algae. Remove the water from your pond, clean it thoroughly, and fill it with fresh water. This removes algae spores, and then you can implement UV clarification to remove any remaining spores from the fresh water.
Conclusion
The weed control method depends on your location, pond size, and ecosystem. Some regions restrict herbicides in ponds, so you must acquire a permit to use them. Alternatively, you can hire a professional to assist you in applying chemical herbicides. You should try out other methods of weed removal before resorting to herbicides.
