Beth Krasna >

Contrary to conventional wisdom -

Aquatic Plants Thrive in a Swiss Koi Pond

by Beth Krasna, Switzerland - Click images to enlarge

Our pond is about 10 meters (33 feet) long in a sort of curvy shape - two round deep ends at the extremities, about 1 meter (39 inches) deep, and a narrower, shallower part in the middle, 50 centimeters (20 inches) deep. It holds approximately 12,000 liters (3.200 gallons). We have about 35 koi of various sizes (a few quite large) living in the pond, with about 30 goldfish, who seem to reproduce at a great rate (randy little things). This is the second year of the pond, and we have had a few baby koi both years.

There is a shallow ledge near the middle of the pond, where we feed the fish. The second year some of the braver larger koi have actually been eating out of our hands. Because of the large number of fish (we keep giving goldfish away, but can't keep up with the birth rate despite having 5 golden orfes for population control), we have a rather strong filtration and aeration system.  

During the winter, or until the weather hits 0 Celsius (32 Fahrenheit) and we start worrying about the pond freezing over, we keep the pump on as long as we can. We shut off one of the water intake pumps, and raise the other to the surface. This ensures aeration, but hopefully not too much temperature exchange, and the bottom of the pond stays around 4 Celsius (39 Fahrenheit). We have a small plunger type heater that floats on the surface to keep a hole open in the ice during the worst of the weather.
The three Pontederia lanceolata are grouped in the middle of the pond. Other than that we have two waterlily plants. We had one lotus plant, but it did not survive the Swiss winter. In summer we tend to let floating lettuce plants and water hyacinths multiply, as they give some shade cover in the heat of summer. The fish quite like playing with it, punting the plants around, eating the roots and making loud chomping noises as they sometimes munch on the leaves.  
The trick to the potted plants is to plant them in jute, then put the jute in a plastic mesh container. This has worked beautifully for us and we have not had any plant damage. All the other plants grow around the edge, either on a very shallow ledge that the koi can't get to (well mostly, they try - the goldfish manage, but don't bother the plants), or around the exterior of the pond. We have some grass around the edge, and the koi come out and nibble on the grass (maybe thus leaving the plants alone).  

We think the koi don't actually want to eat the water plants, but slaloming between them would hurt the shoots. They don't do it with the lilies (swim around the bottom), and the Pontederia are planted very close together - so they can't. They try to nibble the roots, but can't get at them through the plastic mesh and the jute. Consequently, the plant is quite robust. The overall planted impression of the pond is mostly from the shallow ledge and the plants around the pond. 

Beth Krasna is a professional chemical engineer with an MBA. She works in industry, venture capital, and is an independent board member. She coaches start-up businesses as a hobby. A co-founder of the creative commons ThinkStudio, Beth is active with ethics projects including Thinking Ethics published by Profile Books.   

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