With Spring arriving many koi hobbyists will enjoy adding plants to enhance their koi pond environment, but some are unaware of the dilemma adding the wrong plant inside the pond could cause the koi to get ill and worse die.
An overabundance of aquatic plants can also strain a pond’s ecosystem and potentially lead to a fish kill. During daylight hours, plants produce oxygen and raise the water pH, yet at the same time the plants respire, removing oxygen and adding carbon dioxide and lowering the pH.
Dead leaves will also rot and create waste products in a pond, so yes, they will eventually harm fish. However, that depends on how big the pond is vs how many leaves are in there.
Pond experts recommend covering no more than 50% of the pond with plants to aid in providing shelter for the fish and reducing excess nutrients. This also limits algae growth and moderates water temperature on hot days.
Please use this reference chart when selecting plants close or at your pond site, this chart is courtesy of bonniesplants.com
| Toxic Plants to Avoid | Toxic Plants to Avoid |
|---|---|
| Allamanda – all parts | Jack-in-the-pulpit – all parts |
| Aloe – leaves | Japanese laurel – all parts |
| Alocasia – leaves and stems | Indian Turnip – all parts |
| Allspice – leaves, seeds | Iris – leaves, roots, rhizomes |
| Amaryllis – bulbs | Jasmine – berries |
| Anemone – all parts | Java Bean – uncooked bean |
| Anthurium – all parts | Lantana – all parts |
| Apricot – leaves | Larkspur – all parts |
| Azalea – all parts | Laurel – all parts |
| Baneberry – berries, roots | Lily of the Valley – all parts toxic to cats |
| Bird of Paradise – seeds | Lobelia – leaves |
| Black Locust Bark – sprouts, foliage | Locust – bark, leaves, seeds |
| Black walnut – all parts confirmed reports of death | Locoweed – all parts |
| Boxwood – leaves, stems | Lupine – all parts |
| Buttercup – sap, leaves | Marijuana – all parts |
| Cactus | Mayapple – all parts |
| Calla Lily – leaves | Mimosa – all parts |
| California tern – roots, seeds | Mistletoe – berries |
| Cardinal flower – all parts but I have not found that to be true | Mock Orange – fruit |
| Carolina jasmine – all parts | Morning Glory – all parts |
| Caladium – whole plant | Mustard – roots and seeds |
| Cherry – bark, twigs, leaves, pits | Narcissus – bulbs |
| Chenille plant | Nightshade Oak – acorns, foliage |
| Choke cherry – all parts I do have reason to believe that this plant MAY be toxic to fish from correspondence with ponder who lost a lot of fish that ate the cherries that dropped in her pond. Use caution when placing a pond under this tree. | Oleander – all parts |
| Colocasia – all parts I have several different varieties in my pond and my koi do chew the roots. I have not had a problem | Peach – leaves |
| Coral Plant – seeds | Philodendron – all parts |
| Croton – seeds | Pine – sap |
| Daffodil – bulbs | Poinsettia – leaves, flowers |
| Datura – all parts | Potatoes – eyes, new roots |
| Day lily – very poisonous to cats | Privet – berries, leaves |
| Delphinium – all parts | Prunus varieties – seeds, some parts |
| Death Camas – all parts | Ranunculus – all parts |
| Dumbcane (dieffenbachia) – all parts | Redwood – sap (from decks also) |
| Digitalis – all parts | Rhododendron – all parts |
| Easter lily – very poisonous to cats | Rhubarb – leaves |
| Elephant’s – ear all parts | Snapdragon – all parts |
| Eggplant – all but fruit | Snowdrop – all parts |
| English Ivy – all parts confirmed reports of death | Taro – all parts |
| Foxglove – all parts | Tiger Lily – all parts, especially to cats |
| Gloriosa lily – all parts | Tomato – leaves |
| Hemlock – all parts | Trumpet vine – all parts |
| Holly – berries | Tulip – bulbs |
| Honeysuckle I have a reported case of fish deaths after eating the flowers and leaves. Once the leaves and flowers were removed from the pond, and the water changed out, the fish stopped dying. | |
| Hyacinth – bulbs |
So now that you know which plants to keep away from the koi, you may be asking yourself which plants you could have inside or near your pond. My research found the following acceptable water plants that are safe for the koi fish and add beauty and oxygen to the koi pond environment:
- Water Hyacinth
- Water Lily
- Lotus
- Water Iris
- Water Poppy
- Water Smartweed
- Duckweed
- Umbrella Palm
- Elodea
- Fanwort
Remember to use only 50% of pond for any water plants and to keep them under control so they do not overwhelm the pond. Plants help provide shade for the koi which in turn will help control the pond water temperature, as well as provide additional oxygen the koi need.
So, feel free to add plants to your koi pond oasis, just remember to research the plant and make sure it does not hurt the koi inside the pond, and enjoy the koi and the plants together in harmony.