Water Garden Shelves and Plants

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Plants play an important role in helping to balance the overall ecosystem of a manmade pond. Aquatic plants offer natural biological filtration, as they are able to absorb certain metals, phosphates, gases and nitrates from the water that could otherwise build up over time and cause problems. If you run a biological filtration system in your pond, nitrates will be produced as one of the byproducts. Although they are harmless to fish in normal quantities, nitrates, which are essentially a plant food, can cause algae to flourish if they reach high levels. If you place some non-evasive aquatic plants in and around the pond, nitrates will be absorbed by the plants as a source of food, helping to keep nitrate and algae levels in check. 

There are a few different types of plants you can put in a pond. These include floating plants, deep water plants, oxygenating plants and marginal plants. Marginal plants are one of the most common aquatic plants used in manmade ponds because they are easy to plant and they look great. What sets apart a marginal aquatic plant from other types of plants is the way it’s planted; the roots of the plant are placed in water, with the bulk of the plant living in the air above the surface. Because only the roots of marginal plants should be submerged, however, some kind of a planting shelf is recommended to allow a shallow area for planting.

Before we get into shelves, it’s worth noting that this is a bit of a contested topic. There are a couple reasons shelves can get a bad rap:

  • If a pond is improperly designed, predators can stand on the shelves, giving them easy access to the fish for a meal. In our opinion, this is usually due to other causes like too many shelves, too wide of shelves, or insufficient depth in the pond.

  • In a koi pond, sometimes koi can be destructive with plants. This doesn’t happen in all cases; we hear from plenty of happy pond owners whose fish live harmoniously with plants. In our experience, it has more to do with how the pond is designed and planted than with the habits of the individual koi. Koi do like to dig, so if you just plop a potted marginal plant onto a shelf in the pond, sometimes a koi will dig around in the pot, eventually knocking over the plant and uprooting it. However, getting rid of the pot and installing the plant properly so there’s nothing to dig in is often enough to make the koi to leave the plants alone. We’ll talk more about how to plant properly in the building chapter.

How much shallow shelf space is too much?

The main concern people have about shelves is that they can help predators get to the fish more easily. If you’re not planning to have fish in your pond, then none of this really matters and you can have as many shelves as you like. However, if you are planning to have goldfish or koi in your ecosystem pond, the key is to limit the shelving space to what is necessary for the aquatic plants. A bunch of empty shelf space will only provide your friendly neighborhood raccoon family with a perfect fishing location. Instead of lining an entire side of the pond with a shelf, for example, try isolating the shelves to a few key areas where you will concentrate some aquatic planting. In addition, try not to make the shelves wider than is necessary to hold the type of plants you’re planning.

All that being said, fish are not dumb! If there’s a predator in the area, they will know to get away from it. The trick is to give them an area to hide. This can be an area of deeper water (3’ deep minimum), or possibly a fish tunnel or cave installed near the bottom for them to hide in. (12” PVC culverts work great.) A combination of all the above tips will really help protect the fish in your pond while allowing them to live harmoniously with plant life.

Strategically placed planting shelves allow for marginal aquatic plants, while a larger 36” deep area allows fish to evade predators.



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