Aquaponics – Grow Vegetables in Your Pond

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Robert Pavlis

Imagine growing vegetables in your pond. You never have to water them, or fertilize them. Since ponds stay cooler than soil, cool growing crops like lettuce can be grown over a longer period of time. Ponds are a natural source of nutrients, especially if they contain fish, and these nutrients help vegetables grow aquaponically. Not only do you produce food but the growing vegetables help keep algae levels low.

Vegetables can be grown right in the pond or in an associated bog garden without any extra equipment. Or you can get more serious about this and pump water to an external hydroponic growing area.

Lettuce ready to harvest from a Styrofoam raft floating on a pond
Lettuce ready to harvest from a Styrofoam raft floating on a pond

Nutrients in the Pond

Nutrients naturally accumulate in the pond since fish waste, insects and dead plant material will all decompose and produce the nutrients plants need to grow. A common problem in a pond is that there are too many nutrients which results in algae growth.

In a normal pond, equipment such as pumps and filters are used to reduce the nutrients and control algae growth. In a natural pond, plants are used to keep nutrient levels low and in turn control algae levels. The logic here is simple, algae requires higher nutrient levels than most other plants. If the pond plants keep levels low, algae will not grow.

Microbe Science for Gardeners Book, by Robert Pavlis

Building Natural Ponds book by Robert Pavlis

Another way to keep nutrient levels low is to grow vegetables right in the pond water. They not only control algae, but you also get to eat them.

Hydroponics vs Ponds

Hydroponics is being used more frequently to grow our vegetables including lettuce and tomatoes. In such a system, the roots of the plants are suspended in water that contains fertilizer. The rest of the plant grows normally in the air.

How does a pond compare? Provided that there is some way to suspend the plant over the pond water, it is virtually the same as a hydroponic system with one important difference. You don’t need to fertilize the pond since fish, insects, bacteria and decaying plant material do this for you.

Commercial hydroponic systems are relatively complex with pumps moving water past plant roots and equipment testing oxygen and nutrient levels in an effort to maximize productivity. You don’t need all of this for a pond. A simple raft that holds plants in place is all that is required.

Historical Pond Use

You might think that this is a new idea, but societies have been doing this for a very long time. The Aztecs created large floating islands that grew trees as well as chili peppers, squash, corn, tomatoes, and beans. Many societies still use local waterways to provide the nutrients needed to grow plants.

Floating rafts used for food production at Inle Lake, Myanmar
Floating rafts used for food production at Inle Lake, Myanmar

The idea of using natural water systems for growing vegetables is not new, but doing it in backyard ponds is not common.

Building Natural Ponds book, by Robert Pavlis

Vegetable Growing Raft

I will look at a variety of options for using your pond to grow vegetables, but the easiest is a simple raft system. Take a piece of Styrofoam, drill some holes, insert the plants and let it float it in your pond.

Large floating raft on a pond
Large floating raft on a pond

It is best to use a solid form of Styrofoam instead of the cheap stuff that easily breaks into little balls. The lid from containers used to ship fresh fish to stores and restaurants work very well and you can easily get them for free by asking wherever they sell fresh fish. You can also buy larger sheets in building supply stores.

The problem with flat pieces of Styrofoam is that there is no air space between the Styrofoam and the water. Plants grow better if some of the roots are exposed to air so it is a good idea to have a small air gap between the foam and the water. You can glue on a small strip of foam around the edge of the raft, or use twist ties to hold it in place. You can also use the insulation foam covers sold for copper piping. Any such material that floats will raise up the platform so that it is not touching the water.

There are several ways to hold the plants in place. You can use the insulation for copper piping and cut it into 1-2 inch lengths. This foam already has a slit along one side making it easy to insert the plant. The plant with the foam collar can then be inserted into the hole in the Styrofoam. As the plant grows and needs more space it will push against the foam, compressing it.

Using a Bog Garden

Bog filter use for growing plants and cleaning pond water, illustration from Building Natural Ponds
Bog filter use for growing plants and cleaning pond water, illustration from Building Natural Ponds

Bog gardens are frequently added to a pond as way of cleaning the pond and keeping nutrients low. The picture, taken from Building Natural Ponds, shows how the bog garden connects to the pond. Water is pumped from the pond to the bog garden, through a layer of sand where plants remove nutrients. The water then flows back into the pond.

Normally you grow ornamental plants in the bog garden, but there is no reason why you can’t replace them with vegetables. This works just as well as the floating raft described above.

External Growing Area

The two methods described above are fairly simple to implement, but you might not like the idea of seeing your vegetables in your pond. You might also want a larger growing area to increase the number of vegetables you can grow. The solution is to have the growing area outside of the pond.

There are many options for this solution, but in general, you add a pump that will move the pond water to an external tank(s). The water flows through the tank, eventually returning back to the pond. The tanks, which are usually square, hold sheets of Styrofoam with plants inserted. This tank system is very similar to some hydroponic systems, except that the nutrients used come from the pond.

This system is able to grow many more plants than using the pond alone so it needs more nutrients. A great solution to this problem is to increase the number of fish in the pond. In a normal pond this can be a big problem because the fish produce too many nutrients resulting in algae problems. But in a system with lots of growing vegetables, the pond can support a much higher fish load.

The moving water and the large surface area of the external tanks also provides a great way to oxygenate the water, which is also needed for the higher fish load.

A larger pond can support game fish, so the whole system provides both meat and vegetables.

Marijuana and Tilapia

Canada is going to legalize marijuana in 2018 which has spawned a number of commercial grow-ops. One of the most interesting is just outside of my home town.

Medical marijuana grown aquaponically using nutrients from tilapia which are held in the blue tanks, Green Relief Inc
Medical marijuana grown aquaponically using nutrients from tilapia which are held in the blue tanks, Green Relief Inc

Green Relief Inc is growing medical marijuana indoors, under lights. The plants are sitting in rafts floating over large tanks containing water that is pumped from large blue fish tanks containing tilapia. The fish poop in the water produces lots of fertilizer, which the plants then use to grow. Pumps circulate the water keeping both fish and plant roots well oxygenated. They harvest both the pot and the fish.

Flowers and vegetables growing aquaponically at Green Relief
Flowers and vegetables growing aquaponically at Green Relief

This is not exactly an example of growing vegetables in ponds, but the science behind it is exactly the same and Green Relief has even grown flowers and vegetables in the same system. One thing that is interesting in this case is that people did not think you could grow marijuana aquaponically on a commercial scale, but clearly it works. Green Relief is not providing a lot of details on their system, but it looks as if the plants are in pots which sit mostly above the floating rafts. This may be necessary to provide the roots with enough air.

Since each Canadian will be allowed to grow 4 plants for their own use, you might soon start seeing a lot of backyard ponds growing marijuana.

Pots containing expanded clay pellets are used to keep fish from eating plant roots.
Pots containing expanded clay pellets are used to keep fish from eating plant roots.

Fish and Roots Don’t Mix

One potential problem with floating plants on your pond is that fish, especially koi, like to nibble on plant roots. If you have fish in your pond you might need to put some kind of mesh protection under your raft to keep the fish from eating your lettuce roots.

An alternative is to put each plant into a large mesh pot that contains some supporting material, like expanded clay pellets, to hold the roots.

 

More Articles About Ponds

Winterizing Ponds and Water Features

Beneficial Pond Bacteria – A Waste of Money

Pond Pumps and Pond Filters

Selecting the Right Pond Liner

Water Lilies

Building Natural Ponds

If you are interested in natural ponds why not join our special Facebook group Building Natural Ponds. Please join the group at https://www.facebook.com/groups/1760349757565562/

Building natural ponds face book group
Building natural ponds face book group

References:

  1. Image of floating farms; Meindert van D
  2. Image of flowers and vegetables growing aquaponically with permission of Green Relief Inc

 

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

13 thoughts on “Aquaponics – Grow Vegetables in Your Pond”

  1. I agree with pond growing being viable. I wanted to share that there are a lot of problems with the standard home gamer implementation of an aquaponics system. If the point is to grow a few plants in a pond that’s already present and the fish are pets or harvested only occasionally for personal use then it makes perfect sense. If the point is to condense an entire ecosystem into a few large stock tanks and harvest both plants and fish from limited water volume then it quickly becomes inefficient economically, mainly because fish food costs too much. Unless they can find people willing to pay $10-$20 a pound for tilapia or $10 a radish. Or if we ignore input time as a cost, they,d still need to find someone willing to pay $5-10 a pound for tilapia and $5 a radish to offset overhead, mostly in the form of fish food.

    Because I could always be wrong, anytime I hear about a company that claims to be making the standard home aquaponics model work I wait a bit and then see if they’re still in business. Green Relief appears to have folded in 2020 according to the website pwc . I would provide a cite but I worry the forum filter might block the message because it has a link in it. There is also a story about corruption/embezzlement by top executives and, the thing that for me is key, the fact that Green Relief was heavily investor funded. While they could have been economically viable with this model if they invented some new way of doing it that I haven’t modeled (I have no way to know without seeing their balance sheet) I suspect that the reason they were in business wasn’t because they were producing an economically viable product using aquaponics where their inputs were offset by profits, but because they had about 60 million in investment capital.

    I was involved in I-502s rollout in Washington and I did business modeling with inputs using aquaponics vs hydroponics vs soil to grow marijuana. Aquaponics adds costs in the form of fish food, wasted square footage, and labor with the same or slightly lower output compared to hydroponics and those costs are not offset to any meaningful degree by the meat harvested. Also, the water needed for fish to live can’t contain ideal fertilizer concentrations for marijuana growth or be the ideal (relatively acidic) pH, because all recognized commercial fish I could find either die or fail to thrive when exposed to high fertilizer concentrations and pH between 5.8-6.2 (the present level generally thought to be best for marijuana.) There are other problems too but I stopped trying to find a way to make it work at that point. I suppose something could be done with a membrane filter but why bother when hydroponics works better and the point isn’t to produce fish in this use case?

    To be clear, I am not debating that it is possible and often a good idea to grow plants in a pond, or with pumped pond water. That’s essentially what rice paddies are. That works and has worked for thousands of years. I am saying that the home gamer model of aquaponics with lots of fish in tanks, relatively little water volume and no food input that isn’t purchased at a store in a bag labeled “fish food” isn’t an economically efficient business model given the non-ideal growth rate of plants within that system compared to other options coupled with the relatively high cost of feeding the fish per pound of salable meat produced. You speak precisely and I try to as well. I’ve learned a lot from your work and usually I have nothing to add to it. Here I felt that it was worth mentioning that, in my own experience and from every example I’ve seen and the modeling I’ve done it doesn’t appear to be economically viable to run an aquaponics system where the main source of fertilizer starts out as commercial fish food.

    If someone decided to run an aquaponics system attached to a slaughter house and fed the fish, perhaps pike, the waste meat that might work, but even that might only break even given overhead and that even waste meat has resale value.

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  2. I tried growing lettuce in my small pond on floating styrofoam the lettuce turn yellow did not grow at all there are fish in the pot I would like to use my pond somehow

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  3. I live on a small, natural (9-10 acre) spring fed lake / pond in South Western Ontario. It is fairly swampy around the edges (lots of reeds, bullrushes, providing protection for waterfowl), and also has a lot of floating peat and lilypads, as well as a few species of fish. It seems very nutrient dense.

    Could something like this be used for pond aquaponics?

    Reply
  4. Very nice article. I’m thinking of setting up a hydroponic garden, using my half acre pond to feed it. I only have one concern. I use a die in the pond to prevent algae. is this a problem for the vegetables I like to grow and consume?

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  5. One very small point of clarification. Some provinces are restricting their citizens from growing four plants. Each province is setting their own criteria on this aspect.

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