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 Pond Care

Ways to protect your pond from -

Parasites, Pathogens, and Problem Plants
by Rich Sacher, Louisiana USA 

Pontederia cordata
"Pickerel weed"

I just love it when I find a new aquatic plant to try in my pond . . . don’t you? Maybe you know a plant as a land plant, but someone tells you it also grows in water. Or, perhaps a friend offers you an aquatic plant you have never grown. Or it may be an intriguing oddity that you discover in a catalogue or on the internet. In the excitement of your new discovery, you might practice neither prudence nor patience before acquiring this freshly desired object and placing it in your pond.

The advice offered here is specifically for you who have garden ponds which are formed by a liner or concrete shell. Those who have a one- or two-acre earth-bottom pond are dealing with a much more complex ecosystem. They should consult their local agricultural extension agent before introducing any living thing to their earth-bottom pond; once a plant or animal becomes well established, it may be costly or impossible to eradicate if it later becomes a problem. But with a smaller garden pond contained by its liner, you can dispose of the disaster, even if it means making the drastic decision to empty the pond and start over.

Here are some cautionary controls that you should be aware of, to prevent catastrophe in your pond . . . and beyond!


Countless parasites exist that can infect the fish in your pond; and the easiest way to obtain parasites is to bring plants or fish from the wild into your aquatic paradise. You may have expensive koi, or just gorgeous goldfish, but both are susceptible to anchor worm and fish lice. It may tempting to collect water hyacinth, pickerel rush, horsetail, etc., and bring them home to augment your aquatic plant collection. The roots of these plants can easily harbor parasites, fish eggs, snails, crawfish, and other critters that do not belong in your pond. Bog plants may also be infested with caterpillars or spider mites. A single water hyacinth with spider mites can blow around your pond and infest other susceptible plants such as cattails, taro, pickerel rush , cannas, calla lilies, etc.

You are much safer to exchange plants or fish with fellow pond keepers whose ponds you know are parasite free. (Make sure THEY don’t collect plants from the wild! Ask them!) Some aquatic and bog plants in the wild are protected species, so that is another reason to leave them where nature put them. However, if prudence cannot persuade you to stop digging at the edge of that native pond, at least promise to quarantine your purloined plants when you get them home. Keep them in water containers away from the pond, and grow them this way for the season while you inspect them often for unwanted hitchhikers. Experienced fish fanciers quarantine their new fish and observe them for at least a month before introducing them to the pond. I highly recommend this excellent practice, whether obtaining fish or plants from a fellow hobbyist, an unfamiliar store, or though a mail order company. 

Canna 'Endeavor'


Fish are susceptible to pathogens too numerous to name. Various fungi, bacteria, and viruses can infect fish. Some pond keepers never seem to have a problem, while others constantly have trouble. If you overcrowd a pond with fish, overfeed the fish, have poor water quality, your fish will be severely stressed. Bad things surely will happen.

Do not overload your pond with fish. In his book "Goldfish Pool, Waterlilies & Tropical Fishes", Dr. G.L. Thomas suggests a minimum of 20 square inches of surface area for each inch of fish in the pond. Circulate and aerate the water with a pump . . . either through a fountain jet or a waterfall. Use a biological filter or keep an abundance of underwater grasses in the pond; one bunch for each square foot of surface area is the common recommendation. Anacharis, Cabomba and hornwort are the most popular choices. (If you have koi, they will eat the a biological filter can take the place of the grasses.) Both absorb excess nutrients. Clear, oxygenated water helps greatly in keeping fish healthy. Healthy fish tend to have greater resistance to these pathogens. Beware of accepting “free fish” from someone who has too many, unless you are willing to quarantine them for at least a month to be sure they are disease free.

If your fish come down with parasites or a disease, you need to consult an expert for a diagnosis. Once you know the ailment, use a treatment sold to remedy the problem. You also need to decide if you are going to treat the whole pond or if you are going to capture the fish and hold them in treatment tanks until they are free of what ailes them. (There are 7.5 gallons in each cubic foot of water.) Either way, you're facing lots of work. As always, an ounce of prevention is worth a pound of cure!  

"Water hyacinth"


The internet has truly transformed us into a global village. Plants from around the world can be ours with a few strokes of the keyboard and a click of the mouse. And a credit card number, of course. Buying foreign plants online is wonderful, exciting, and dangerous! Buying a pig in a poke is always risky, because you never know what you will get . . . and with aquatic plants, it could be a whole lot of trouble. Consider the legalities involved: if you buy a water hyacinth in New Jersey, it may only cost you $5.00. If you sell it in Florida, it could cost you a hefty fine! A desirable aquatic plant in one part of the country may be a noxious and illegal weed elsewhere. Of course, this applies to exotic terrestrial plants, too. 

How can any of us keep up with which plants are legal in which states? Do we have a license to bring plants into the country? Or into our state? Could any of these plants escape our pond and become a widespread economic and environmental nuisance? If you have never seen a particular plant, and perhaps do not even know its name, you ought not take it home and put it in your pond. Do your research first and be sure you are making an informed decision. A good place to start is Invaders Database System, Noxious Weeds in the US and Canada. Other countries will similar resources.

The lovely water hyacinth is a well known example of an exotic aquatic which has spread out of control in the southern United States. It chokes many waterways to the point they are no longer navigable. Today we face another pernicious plant, the newly introduced floating giant salvinia (which probably escaped someone’s aquarium) that thrives in Texas and Louisiana. This illegal (in the US) South American aquatic grows into a floating mattress almost a foot thick, killing all plant and animal life beneath it. Boaters innocently give these hitchhikers a free ride, spreading them to the next lake or bayou. With no natural predators, it freely spreads like wildfire wherever it finds water in a favorable-to-it climate. Surely, none of us in any country wants to be so careless that we introduce the next aquatic plant scourge to our own part of the world!

Aquatic plants in the wild may spread easily and unpredictably. Therefore pond and aquarium keepers find themselves an important line of defense in preventing the introduction of aquatic weeds into our environment. Along with a passion for our hobby comes the responsibility to know that the plants we grow are safe and legal where we live. So, be kind to Mother Earth . . . promise her that you will never release unwanted plants into the wild. Use them for a plant swap, donate them to a botanic garden . . . or put them in your compost pile!

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