Plants can add beauty to a koi pond and also improve its overall environment. Plants provide oxygen for the water and utilize the nitrogen produced by the fish from their food. They also provide shade and cover from predators for the koi. It is ideal to include a combination of a mix of surface, emergent, and submerged plants in your pond. If you're ready to add plants to your koi pond, consider the options below.
Surface Plants for Koi Ponds
Surface plants are often referred to as floating plants because they simply float on the surface of a pond. Koi will eat the leaves of these plants but rarely kill them. They provide shade to the koi and help keep the water cool in the summer, though they can overtake a pond if not limited. These plants shouldn't be allowed to cover more than 1/3 of a koi pond, as a greater density could deplete oxygen. Examples of surface plants that work well in a koi pond include:
Water clover (Marsilea spp.) plants look like a four-leafed clover. Water clover plants can float on the surface of a pond or be held above it on stems. There are more than 65 species of water clover in this aquatic plant genus. They are beautiful but can be aggressive enough to overtake a pond if not kept under control.
Water fern (Azolla filiculoides) is a free-floating small fern that thrives in freshwater ponds. This aquatic plant is sometimes called red fern, though it's not always red. It can also appear green or brown, depending on environmental factors. This small fern is approximately an inch long with leaves that quilt to hide the stem.
Watershield (Brasenia schreberi) is sometimes referred to as dollar bonnet. It's a relatively small leaf plant about five inches in size. The leaves are slimy on the bottom. They have an oval shape. The stem and root portion provide areas for small animals and invertebrates to congregate, where they are eaten by the koi.
Emergent Plants for Koi Ponds
Emergent plants have firm rooted stems below the surface of the water but stand above or float on the surface. Bog plants fall into this category. Koi enjoy eating the roots of these plants, so they should be potted in containers two sizes larger than the plant needs, with rocks over the top of the surface. This makes it difficult for koi to dig for the root. The koi will still eat some of the leaves, but this should not hurt this type of plant, as long as a third of the plant remains on the surface of the water.
The American lotus (Nelumbo lutea) is a beautiful emergent plant to add to a koi pond. This aquatic perennial is sometimes referred to as a yellow lotus or yellow water lotus due to the lovely color of its flowers. Their leaves and flowers both rise above the surface of the water, even though at first glance they may appear to be floating.
Common cattails (Typha latifolia) thrive in around a foot of water, though they can grow in less water or even marshy soil. These perennial wetland plants can grow in full sun or partial shade and can grow up to 10 feet tall. You can plant the bare roots underwater around the edges of your koi pond, though koi do enjoy munching on the roots of these bog plants, so using a container is recommended.
Water lilies (Nymphaeaceae) are lovely emergent plants for koi ponds. There are 58 different species in this family of plants. Water lilies give the appearance of floating on the water, but are actually grounded by a rhizome. Water lilies should ideally be planted in a pot or other container that is positioned between six and 18 inches below the surface.
Submerged Plants for Koi Ponds
Submerged plants, also referred to as oxygenating plants, grow completely immersed in water. They absorb the nutrients they need to grow through their leaves. Submerged plants provide oxygen for the water while also filtering it. They compete with algae for nutrients, which helps to keep algae under control. Recommended varieties include:
Coontail (Ceratophyllum demersum), also referred to as hornwort, is a long, rootless plant with serrated leaves all around the stem. Coontail plants resemble a bottle brush or the tail of a raccoon (hence the common name). These aquatic plants are dark green and can form dense colonies.
Water smartweed (Polygonum amphibium) is a perennial that can grow to three feet high in dense colonies. It has alternate lance-like leaves in medium green. This plant can actually grow submerged or floating on the service, making it one of the very few amphibious plants that exist. When water smartweed blooms, bright pink spikes protruded above the leaves. Koi enjoy eating it, but that helps keep it under control.
Common waterweed (Elodea canadensis) is a perennial plant that can grow fully submerged in deep water or partially submerged in more shallow water. Its size varies greatly, ranging from as little as four inches to as long as three feet, depending on the depth of the water in which it is growing. This aquatic plant is translucent green with oval leaves that grow in groups of three surrounding the stem. During the summer, it forms tiny white blooms that peek above the surface.
Adding Plants to an Established Pond
The best way to add plants to an established koi pond is to add a group of plants at once so no one plant bears the brunt of the koi's curiosity (and bite). Not all koi pond owners agree as to whether they should have plants. New plants are novelties for the curious koi and are quickly eaten or tipped over. This is not so much a problem when putting koi in an established pond with many plants already in it, but it can be a challenge when adding plants to an established koi pond that doesn't have many plants.
This approach also helps make the pond look finished, whereas adding one or two plants at a time can accentuate the lack of vegetation in the pond.
Plants to Avoid
Not all plants belong in water gardens. Avoid invasive plants such as the Eurasian watermilfoil (Myriophyllum spicatum), giant reed (Arundo donax), hydrilla (Hydrilla verticillata), and water hyacinth (Eichhornia crassipes). These plants can spread into nearby creeks and lakes and cause big problems.
- In some places, it is even illegal to use these plants. and others that are invasive.
- To see if a plant is invasive, check the United States Register of Introduced and Invasive Species.
In addition, some plants may be toxic to fish. The Midwest Pond & Koi Society has a list of poisonous plants on its website. You may also want to check with experienced koi pond keepers before using an unfamiliar plant. If you cannot find information on whether a particular plant is poisonous, reconsider using it in your pond.
Plant Maintenance in a Koi Pond
The plants in your garden pond will aerate the water and remove harmful nitrogen from it. This reduces the need to change the water in small ponds and leaves the pond a healthier place for the koi. The plants should not need any extra fertilizer. If you do add aquatic fertilizer, be sure it is safe for fish.
Isolate Sick Koi for Treatment
A common cure for sick koi is to add salt to the water. If you do this, you will kill your plants. Do not add salt to water that contains plants. Instead, isolate the koi that are sick and treat them in the location where you move them before reintroducing them to the pond.
Dealing With Algae in a Koi Pond
Algae is an unwanted but inevitable presence in most ponds. Koi will eat some of it, plus shading it with emergent and surface plants will help control it. These types of plants compete with the algae for nutrients and so help to control it that way.
Plant Density in a Koi Pond
A small koi pond needs to have about 70 percent of its surface covered by plants to provide shade to the koi and to keep the water cool enough in the summer for the koi to be comfortable. Larger ponds do not need as many plants because the depth of the pond provides shade and cooler water for the koi.
Koi and Plants Can Coexist
With a few simple precautions, koi and plants can coexist. Place large numbers of plants in the pond to spread the burden of the koi's curiosity and place rocks over roots and tubers to protect them. You should also be willing to occasionally replace a plant or two. After all, fish will be fish - which means that they're going to snack on aquatic vegetation. Make sure you do not plant poisonous plants in your pond. Do these things and your plants and koi can both inhabit your pond peacefully.