Are koi compatible with plants in the same pond?

Are plants and Koi a good mix? In what ways can they co-exist in a Koi pond? What are the advantages of having plants in a Koi pond? Which are the most suitable varieties?

Are plants and koi a good mix?

As often seems to be the case in koi keeping, there isn’t a straightforward answer to this question, as it depends on several factors.

- A koi’s perspective. Koi are bred and selected for their beauty (and our enjoyment). While years of selective breeding for colour may have led to negative side-effects on the vigour or disease-resistance of koi, unfortunately it has done nothing to curb their instinctive feeding behaviour which they still, unashamedly share with their wild-type carp ancestors.

Consequently, in koi, we are dealing with beautiful aquatic pigs that not only ‘need’ to graze and root around your pond, but will also readily consume fresh vegetation in their diet whenever it is available.

-          A plant’s perspective. If koi are in your locality, it is highly likely that you will suffer from their gastronomic attentions – losing a leaf or two. But koi will not just be content at grazing the juicy, soft shoots and leaves of your submerged aquatic plants, they will also, instinctively, turn their attentions to the planting media.

Koi have a protrusible mouth which extends forwards and downwards enabling them to root and push around in amongst the soft substrate of a pond. Usually, by design, most artificial pond bottoms are made from a very unforgiving and unappetising artificial membrane (no food there!). But, whenever koi are prevented with islands of inviting baskets of soft and seductive aquatic soil, topped off with gravel – well there’s no stopping them. There’s no surprise when they can’t help themselves, instinctively rooting around. Their protrusible mouth will select, mouth and clean gravel, looking for snails and other invertebrates. In the process, the dislodged gravel will expose planting soil which will in turn attract more koi – resulting in an organic cloud and uprooted plants – Hardly the idyllic pond you had hoped and planned for.

Can Koi and plants coexist in a pond?

The koi keeping purist insists on a plant-free pond. A plant-free pond certainly has the benefits of low maintenance, cleaner lines and puts koi unmistakably centre-stage. A plant-free koi pond also removes the risk of koi littering a pond with soil, gravel and uprooted plants. Furthermore, surface area taken up by a marginal shelf is, from a koi keeper’s perspective, wasted space which could be 5’ deep instead of only 9” – providing their koi with even more valuable pond volume.

But, if you were to informally survey ponds in which koi are kept in the UK, then the vast majority are likely to contain pond plants. Why? – and what are the secrets to combining plants and koi?

  1. Size and number of koi. Koi and plants will usually only prove to be incompatible if koi are too numerous or too big (larger than approx 8”). Any larger than this and their size makes them more destructive.
  2. The correct choice of plants. Generally, those plants that are found below the water’s surface are fair game for koi. Water lilies and oxygenating plants of any description, given the opportunity will be stripped, uprooted and dislodged by larger koi. The best options to achieve a successful, harmonious planted koi pond is to do one of the following:
  3. Stick to marginals. Limit your pond plants to a selection (and a wide one at that!) of marginal plants. These semi-terrestrial plants will have tougher foliage and if planted carefully, will prove to be koi-proof. Ensure that any gravel used to top-up baskets is too large and heavy for koi to move and that where possible, the tops of the baskets are above the water level, making them off-limits for your koi. You will however, have to keep an eye on spawning behaviour as koi will instinctively spawn in and around the hard plastic planted baskets – potentially damaging themselves in the process.
  4. Create a bog area. One way of keeping your beautiful pond plants and your ASBO koi apart is to retain your plants in a bog area which is still linked to your pond, but physically separated from your koi. Your plants can then enjoy complete unhindered growth – to the frustration of your koi.


What are the advantages of having a planted pond?

1)      Aesthetics. If you do not consider yourself a koi purist, and have a pond (containing some koi) as an aquatic extension of your planted garden, then you will naturally want it to contain plants. Informal ponds in particular benefit from their hard and at times, all-too-obvious edges and outlines being broken up and blended with adequate planting.

2)      Pond Health.  Plants are an essential part of any natural aquatic ecosystem. Consequently, any pond will benefit from being planted. Plants will take up any accumulating nutrients from pond water, and help to compete against unwanted plants (aquatic equivalents to weeds) such as green water and blanketweed. A good balance of pond plants also attracts other pond and aquatic life to your garden. This diversity of insect and invertebrate life in and around your pond will help to stabilise and augment your pond’s environment – having an overall positive impact on the health of your fish.

BoxOut: 10 top tips for running a planted koi pond.

  1. Accept that a fully planted pond containing large koi will be virtually impossible to achieve. You’re going to have to plan carefully for both to coexist.
  2. With no submerged plants, algae will be a real threat. Install a UVc and choose an effective blanketweed control
  3. Spend your money on marginal plants.
  4. Choose some marginals that grow across the water. These will then cut down the light entering the pond.
  5. If you really want lilies and other submerged plants, stock your pond with smaller koi. But bear in mind, these will eventually grow (as will their appetite for your plants)
  6. Why not protect you marginals in a bog area – away from hungry mouths.
  7. If you plant your marginals in plant baskets, try and ensure the tops of the baskets are above the surface of the water.
  8. If the tops of the baskets are below the water, cover them with generous covering of heavy gravel.
  9. Keep your fish well-fed – they are then less likely to feed on any plants.
  10. If blanket weed starts to plague your plant-free pond – hope that your koi like the taste of it as much as they do of your other aquatic plants!

Kill blanketweed and string algae.