Pond Weed Control

Weeds can be roughly divided into the invaders coming from outside your ecology and to plants that are a part of your ecology that have become prolific.  The method of control is different.  Many plants came to us through the aquaria fish trade such as Elodea and Parrot Feather.  Many of the other invaders were first brought as decorative plants such as the lilies and water primrose.  And still other like canary reed grass and blackberry are from far away.
Everyone asks how to treat weeds like there is a magic elixir chemical that will rid you of them.  The chemicals don't work.  Sure they kill for a while but killing isn't the way to achieve pond health.  Many weeds produce prolific seeds and that is why they are successful; others have complex root structures; bulbs unaffected by the chemical; and still others have protective barriers repelling herbicides. You can use herbicides; however, a strategy for control is necessary.  You have to treat the reason the weeds are there.  Energy enters the pond in two forms, sunlight and chemical energy from fertilizer.  If you limit either or both, you will control weeds. 




String or Filamentous Algae



Planktonic Algae

There is more algae on the planet than than anything else alive.  The algae are responsible for over 85% of the atmosphere and everything on earth that has dinner has either directly or indirectly eaten algae.  It is called a primary producer.  And the reason it grows is from one thing: fertilizer.  Removing the fertilizer with plants and artificial aeration stops the problem.  Algaecides do not work because when you kill the algae they decompose and that fertilizer makes more algae.  Additionally, the chemical that kills algae also kills algae predators; and because they are complex animals they do not return but the algae does.  So you actually hurt yourself more by killing the algae.

The Invaders


The above two plants destroy more ponds than any others. Canary reed grass (foreground) and blackberry often completely cover the banks and waterways.  They need to be removed completely and replaced.  They do show you where the nutrients are entering the pond and where to place blocking plants such as willow, cottonwood and alder.  Dense planting of sedge and rushes also stop their growth. All weeds are treated using this replacement technique.  The idea is to replace a bad plant with a good one that adds to your ecology rather than destroying it. 

"Replace bad with good."




There are several species of Elodea.  Most of them were brought to our ecology with the aquarium trade and they escaped.  They choke entire ponds.  Elodea should have no place in your ecology; however, they do occupy a niche that you have to create with other native plants.  You can supply this same habitat with other plants.  Mowing only increases the number of weeds.  A cut herbicide is used to eradicate where the application requires great caution.  This is followed by planting the shore so the fertilizer is removed on shore and not in the pond.


Parrot Feather

Parrot Feather is a popular water garden plant and aquarium plant that is native to South America. It has no place in the natural temperate ecology being a tropical plant.  Parrot Feather has  to be killed completely and replaced.  Limiting nutrients, sunlight and killing with a cut herbicide works.  Often you require blanketing the plant with blue tarp after treatment with herbicide.  This plant is tough and requires constant effort.  Like Elodea mowing only increases the number of plants.  Artificial removal of the nutrients with an aerator is often needed with planting.  You often see it in nutrient rich environments.



Lilies completely cover ponds.  Their presence indicates excessive nutrients.  Total eradication is often difficult without nutrient limiting methods such as aeration with bacterial clarifiers and wood substrate.  Using glycocide and cut herbicides with non-ionic detergents will kill them.  However, without removing the nutrients, they come right back.  It is a constant struggle for several years.


Water Primrose

Water primrose is one of the most aggressive weeds as hard to eradicate as parrot feather.  It was brought in as a watergarden plant having no natural predators. Glycocides and cut herbicides are used with extensive physical removal. Then replacement is used again.  This is one of the most difficult weeds to control where if you have it you should call the professional weed control experts to help you. 


Yellow Water Iris

Yellow water iris chokes waterways and ponds.  Physical removal with replacement is necessary.  The bulbs are highly resistant to herbicides and therefore nutrient control and replacement are needed.

Native "Weeds"



Floating Leaf Pond Weed



Sago Pond Weed

Sago and floating leaf are great habitat and belong to the same group of plants, Potamogeton.  They are stimulated by brackish minerals coming from run-off from open ground.  To control them, you use ground cover on your open ground and plant to remove nutrients.  You do not want to remove all of them.  A few small areas greatly benefit the pond.



Hydrilla coontail is easy to control by removing nutrients.  Often one cut herbicide treatment at the beginning of the year will remove it.  To keep it away, the pond needs to be planted. 


Duck Weed

Duck weed and other floating single leaf plants usually grow in high nutrient water that is low in dissolved oxygen.  Often aerating the water is all that is necessary to remove them.  A little around the base of your plants is desirable pond forage for ducks.  However, to keep them out of the pond, you will have to plant.



Cattail often volunteer in a pond and proceed to take over.  The best way is to physically remove them and then when new shoots emerge wipe AquaMaster on the leaves with a cloth or sponge.  Make sure you remove the dead cane because often seed matures on it.  Do not spray them because you will overspray in the water and kill beneficial plants. This is another plant that shows where the nutrients are in the pond.  Plant accordingly behind them on the shore and they will slowly be replace.


Spreading Rush

Often the Juncus rushes, soft stem bulrush and hardstem bulrush will dominate.  They are great plants; however, they need to have competing plants that will keep them in check.  Any plant in your environment will dominate if left unchecked.  One of the common ones is willow as shown above. 
This concludes The Pond Doctor discussion on weeds.  To control weeds you require a balanced ecology.  If you need help.  Give me a call and I will see what can be done.

The steps to Balance Ecology

Man made ponds need these structures for pond health.
Bottom Ecology

Provide geologic structure with river run rock for invertebrate habitat.


Plant Ecology

Plant these rock beds with native perennial plants and ornamentals.

Pond Respiration

Bottom diffused air with barley and bacterial clarifier to remove fertilizer.

Invertebrate and Reptile Habitat

Locate a dead deciduous log and try to rot it in the pond at the surface by planting on it.  This is home for 4,000 bugs where some eat algae and many are fish food.  The log is also turtle furniture.

Aquatic Animals

Plant fish at minimal density, not to exceed habitat.


Plant crayfish.

Bird Predator/Prey Relationships

Install bird houses.

To completely eradicate weeds you need all of the components of a balance ecology.  This is all relatively easy to perform.  People habitat.



















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