How to Control Pond Weeds

Nora Held
Nora Held
Research Writer
Apart from being our main writer, Nora also works for a number of gardening-related sites and magazines, sharing her experience as an owner of a small farm in North Carolina read more
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Bruce Williams
Bruce Williams
Expert Consultant
Bruce owns a small farm and loves to grill since his early childhood. He’s a professional cook, but hiking and enjoying the great outdoors is his no less favorite part of read more
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Seeing as though weeds Trusted Source Weed - Wikipedia weed is a plant considered undesirable in a particular situation, “a plant in the wrong place”. Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks. are present in almost all natural water bodies, it seems like they need to be a part of your pond as well. This is true, however, leave them alone for too long and you will find out just how destructive to your pond eco-system they can be. The consequences that may follow the presence of large weed populations include limited sunlight for other life forms in the water and oxygen shortages. Of course, this leads to the death of other plants and fish. Lastly, once they are properly established, the weeds are damn near impossible to remove.

As a pond owner, you are thus required to familiarize yourself with pond weeds control measures if you are to have a healthy eco-system. Notably, the weed types that may establish themselves in your fish pond include algae, floating weeds, submerged weeds and lastly emergent weeds. We delve into the characteristics of each type of pond weed and how to get rid of them below.

Why control your pond weeds growth

How to Control Pond WeedsYou may be using your pond to achieve one or more of the following goals: provide water for the plants and animals in your farm, create an ideal breeding ground for various species, mitigate pollution, provide support to the eco-system in your area, for fishing, boating or swimming, and to make the landscape more visually appealing.

Depending on how prevalent the weeds are, they could be detrimental to the primary purpose of the pond. For instance, if you intend on swimming, boating or fishing in the pond, the weeds will likely get in your way and can be dangerous. Next, they can reduce the oxygen in the water, making it impossible for other plants and fish to live there.

Finally, they can make your pond ugly to look at, and since they produce quiet water areas, they will be a haven for mosquito breeding. As you can see, the whole pond and area eco-system will be affected by the presence of weeds, and hence you need to control them before they become a problem.

Floating weeds control

How to Control Pond WeedsIf your pond is relatively shallow, you might encounter floating weeds from time to time. They show up on deep water bodies as well but only in rare cases. Like their name suggests, they will be floating on top of the water and may spread out to cover the whole pond with time. If this happens, they will block sunlight and oxygen from reaching anything underneath them, including fish, plants and water micro-organisms.

You don’t want the problem ever to get this dire although a few floating weeds here and there can provide some visual appeal. Water lilies seem to be the most well-known species of floating weeds. There are others such as duckweed, water lettuce, hyacinth, spatterdock, and waterweed.

If you’re wondering how to control these floating pond weeds cheaply, you may have to opt to cut, rake or pull them from the water. The pulling and raking methods work best for duckweed and water lettuce since they have the least developed root systems of the bunch.

For the rest, simply pulling, cutting or raking them won’t be enough as they have more developed rhizomes Trusted Source Rhizome - Wikipedia In botany and dendrology, a rhizome (/ˈrzm/, from Ancient Greek: rhízōma (ῥίζωμα) – “mass of roots”, from rhizóō (ῥιζόω) “cause to strike root”) is a modified subterranean plant stem that sends out roots and shoots from its nodes. . Instead, you’ll have to add a suitable herbicide to the roots after cutting the top part to ensure they die out as well.

If the pond is too big to go pulling out, cutting or raking the weeds, you may have to spend some money on an aerator, vacuum, or a skimmer.

The skimmer works to create tension in the water which then brings water into the machine. As this is happening, the machine will sieve the water of any debris, leaves or impurities, and by the time it comes out the other side, it is free of weeds.

The large leaves and debris will then be stored in a basket in the machine. As for the small particles, they will be caught by a sponge. Remember to empty the basket and rinse the sponge in the machine occasionally, or else it will clog up, and its efficacy will be reduced.

Alternatively, you can use a water vacuum which works more or less the same way as a skimmer. It will suck in the water, sieve out impurities as well as sludge and when it is released back into the pond it is cleaner and healthier for the eco-system.

The OASE 032232 has been recommended by various reviewers since it works for ponds as deep as 7 ft and even comes with a 16 ft suction hose. The 1300 Gph flow rate should also ensure you don’t spend too much time cleaning the pond.

If the floating weeds haven’t gotten to the point of being problematic, you can prevent that eventuality altogether by getting an aerator. This machine pushes bubbles of air into the pond, which results in some of the air dissolving. Consequently, the pond has more oxygen for the fish and micro-organisms. Also, the constant stream of bubbles will mean the water in the pond is constantly moving; hence is uninhabitable for the floating weeds.

Notably, the Airmax KoiAir Mini aerator has been preferred by many who want a compact aeration unit for their 1000-4000 gallon ponds. If the weeds have already infested your pond and it’s too late to use any of the above measures you can use herbicides instead.

Of the two versions of herbicides available, systemic ones will be the most effective at killing the weeds. On the other hand, contact herbicides may not kill the weed roots, but they are cleared from the water system rather quickly. They thus pose less of a danger to the micro-organisms and fish in your pond.

Submerged weeds control

How to Control Pond WeedsAs for submerged weeds, they always seem to be just under the water surface, although some of their stems may occasionally rise above it. Some common submerged weed species include Hydrilla, Pondweed, bladderwort, watermilfoil and coontail. Notably, certain species of these submerged water weeds are more aggressive than others, so ensure you always take care of them on time.

The submerged weeds characteristically have soft stems which makes them easy to remove using manual methods. Cutting, raking, skimming and pulling by hand are all effective countermeasures. Additionally, shading does make it harder for these weeds to grow. As such, something as simple as planting trees around the pond could be the answer to your recurring submerged weeds problem. That said, you don’t want to overdo it and stunt the growth of other essential plants in the pond.

Another approach to shading is getting pond dyes. These will color the surface of the water, therefore limiting sunlight reach for the deeper areas of the pond. As such, the weeds will die out except in shallow areas of the pond. However, you can always pull them out to finish the job.

Herbicides are often a last-ditch resort if the weeds are persistent. Seasonal herbicides, for instance, are longlasting and keep the weeds away for a whole season. However, the chemical being in the water for as long as an entire season could be detrimental to other plant and animal life in the pond. Some contact herbicides also seem to get the job done.

Emergent weeds control

How to Control Pond WeedsLike the other two weed types we mentioned, the term emergent is quite descriptive of their nature. Typically, they will appear in shallow areas of the pond, and you can see most of their stems above the water. They have an uncharacteristically fast reproduction cycle, and if you leave them alone for a while, you’ll be surprised at how fast they spread.

Some of the most common emergent weeds include purple loosestrife, alligator weed, cattail, phragmites, and bulrush. The rhizomes on emergent weeds are thick and are usually how the plants reproduce.

Most of the time, you can’t get away with just cutting them as they will soon grow back up. That said, during the summer, the plants typically don’t have much energy to resprout and cutting them may serve to reduce their population. Don’t expect to solve this problem overnight, and it may take several years to finish the weeds.

How you dispose of the weeds after cutting them will also play a key role in reducing them. If you dispose of them carelessly, the seeds will spread back to the cuttings, and the weeds will grow again. Lastly, they can last in the ground for a long time before sprouting back up.

Pulling them out is another effective countermeasure. Ensure you get the whole rhizome when pulling these weeds out; otherwise, you’ll be back to square one within a short period. If they are well established, you’ll likely struggle with this task. Nevertheless, you can hire some labor to help you out.

Again, herbicides can help eliminate the emergent weeds within a relatively short period. You can apply systemic herbicides to the plant body, and this will eliminate even the rhizomes. Do note that these herbicides can adversely affect your fish and other aquatic lifeforms in the pond.

There are also other dangers to using herbicides; hence they are heavily regulated. As such, using them without a permit may land you in trouble. In addition to that, consider contacting a professional as they know all the right precautions to take.

If you haven’t yet built your pond, you can avoid dealing with emergent weeds from the onset. All you have to do is use several inches of gravel on the shallow ends of your pond or use the thickest pond liner you can find. However, other plants won’t be able to grow in these areas as well.

Algae control

How to Control Pond WeedsNotably, both planktonic and filamentous algae are an excellent source of food for your fish but can get out of hand fast if you let them. They also generate oxygen which should be beneficial to the pond eco-system.

It’s important we acknowledge that you may encounter several different types of algae all with varying characteristics. Most likely you won’t be able to tell when algae levels have surpassed acceptable limits by looking at the pond. This necessitates that you keep pond water testing kits around you for regular testing. These kits will tell you when it’s time to take action against the algae.

Depending on the level of infestation, types of algae and resilience against other remedies, there are up to five courses of action that you can take to reduce the population. We will go through them one by one from the simpler alternatives to the drastic measures you may have to take.

UV clarification, for instance, is one way to get algae under control. Notably, UV clarifier machines consist of pipes with high-intensity UV bulbs built into them. The water is passed through these pipes, and in the process, microscopic algae are killed by the UV lights.

Since UV clarifiers barely affect fish and other micro-organisms in the water, they are usually the first option before pond owners try anything else. Algae also require sunlight to grow. As such, you can use shading as a deterrent. As is the case with submerged weeds, planting trees around the pond is a longer-term solution.

If trees aren’t an option, you can try dyeing the pond. Do consider that if you reduce the sunlight available for algae you’re also decreasing it for other plants as well. As such, you’ll note a decline in overall plant population in your pond by the time you’re done.

String algae bunch up together and form mats which can lead to their undoing. You can use a rake, vacuum or your hands and you will be able to pull them from the water for disposal. However, be careful as the mats can grow too heavy or too large for one person to pull them out.

Often the last resort for controlling any of the weed types we’ve mentioned above, you can use herbicides for algae as well. Copper sulfate seems like the go-to herbicide since it is both affordable and easily available in the market. There are other variations of contact herbicides that you can use, such as Alkylamine salts and Sodium Carbonate Peroxy-hydrate.

Again such chemicals pose dangers to other lifeforms and can affect them directly. Additionally, the decomposition of the dead algae will likely use up all the oxygen in the water. You are thus advised to read all instructions and be careful in your use of these herbicides. Additionally, it may be up to you to remove the dead algae from the pond as soon as possible.

If possible, use an aerator to get the oxygen levels in the water back to normal asap. There’s a small chance that even herbicides will be unable to complete the job. If so, you can transfer your fish to a different location, drain the pond, clean it, refill it with clean water then return the fish. You’ll eliminate almost all algae and their spores using this method. If you add UV clarifiers, you’ll all but ensure the algae population stays under control for a long time to come. Nonetheless, draining is rarely feasible for many pond owners.

Final thoughts

Again, there is such a thing as a healthy weed population in your pond. As such, you don’t always have to go to extremes to eliminate them the moment they start appearing on your pond. That said, we advise that you keep a keen eye on them and take action as soon as their population starts getting out of control.

Some of the pond weeds control methods mentioned above can also work as preventive measures. Examples include aerating the pond, planting trees around it and using thick pond liners. You can take advantage of these to ensure you never have to deal with an out-of-control weed population. Also, try to limit chemical use and herbicides as much as possible. While they are acceptable as a last resort, using them too much is bound to affect the micro-organisms and fish in the pond negatively. We wish you all the best as you deal with those pond weeds that have been stressing you in the recent past.


Weed - Wikipedia
weed is a plant considered undesirable in a particular situation, “a plant in the wrong place". Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks.
Rhizome - Wikipedia
In botany and dendrology, a rhizome (/ˈrzm/, from Ancient Greek: rhízōma (ῥίζωμα) – “mass of roots", from rhizóō (ῥιζόω) “cause to strike root") is a modified subterranean plant stem that sends out roots and shoots from its nodes.
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