Water plants and koi - the proper way to utilize plants in your pond


For many new comers to the hobby water lilies and fishponds are like the proverbial horse and cart you can't have one without the other. Yet in the ponds of those who have some experience with koi you may not often find water lilies or any other water plants, for they are not as compatible as it seems. There are several reasons for this. Firstly, koi are essentially plant eating fish, and will uproot and destroy all but the hardiest water plants. Secondly, water plants often die off and the decaying plant matter can adversely affect the water quality. Thirdly, having pots in the pond provides the fish with a hiding place which becomes problematic when you are trying to net them.

So, there are some reasons not to have plants in the actual pond, yet their aesthetic qualities can be somewhat compelling, and if you are dead-set on including some flowering water lilies or irises, then there are ways of doing so which minimise the drawbacks.

First of all the plants must be placed in pots and the pots themselves need to be thought about before they are purchased and used. Non-glazed clay pots are preferable, as they don't contain any chemicals that may be released into the water over time; metal and glazed pots are thus not suitable. The pots should also not have any sharp edges that can injure the fish, and should be placed where they will not block any bottom drains or impede water circulation too much. They can also be placed upon bricks or stones to bring the actual plant up to the desired growing depth.

Once the plants have been placed in the pots you will need to pack large stones around the base of the plant, which will prevent the fish from digging in the soft soil of the pot, uprooting the plants and disturbing the soft sediments that accumulate in the pots.

Another significant reason why not to use plants in the pond is their use of oxygen. While plants release oxygen into the water in sunlight, at night or in the absence of light they consume oxygen. This is problematic during warm conditions, such as is found over much of the country through the summer. Under such conditions the dissolved oxygen content in the water is low, while at the same time the fish are active and their demand for the gas is high. When combined with overcrowding and / or lots of plants and stringy algae there is a serious risk of loosing fish to suffocation. They can also further stress the fish by affecting more rapid pH changes between day and night time conditions. So in essence it is advisable to have perhaps only one or two large water plants in the pond or cut down on the number of fish!

Plants with spreading, surface leaves such as water lilies inherently hold both an advantage and a disadvantage. Their leaves provide shade and cover for the fish through the hot days of summer, but also a place for the fish to rest out of sight. The key is thus not to have too much of the surface covered by the lilies so that the fish will at least be able to show themselves most of the time.

If the reasons for leaving water plants out of your koi pond equation seem to be telling you something, then there are other ways to combine the two. By including water plants in your filter, stream or in a special 'sink' on the edge of the pond these dissuading factors can be largely circumvented.

In terms of the bio-filter, plants can be kept successfully in the last chamber. Here they can still be appreciated (depending on the relative position of filter and pond, of course) while performing some valuable duties in maintaining optimum water quality: plants utilise nitrates and phosphates and effectively remove these pollutants from the water.

By locating them in or next to the return stream from the filter to the pond they can also be well appreciated while not being in the actual pond.

In construction of a pond one can start from scratch with marginal plants in mind. All that needs be done is the construction of a special shelf, step or sump if you will, which holds plants in pots at the edge of the pond.




A simple plant filter


Water Lily




The beauty of this pond is enhanced by the plants





Arum Lily

Pictures from Erna Hardy of Chelsea Water Gardens


A Simple Plant Filter



Types of Plants Suitable for the Pond

As mentioned, koi are avid plant-eaters, which means that only the sturdiest, most robust species will stand any chance of doing well in the pond. Fine leaved and delicate species are simply not suitable.

Water Lillies, of the family Nymphaeaceae:

Waterlilies come in 40 different species and are found worldwide. Flower colour is also variable, from the white and dark red of the species that open at night to the blue, pale red and yellow of those that open by day.

There are also various colour deviants and hybrids available. They can be propagated from rhizomes and tubers. Popular species are Nymphaea capensis, N. caerulea and N. indica. Some grow very tall and are suitable for deeper ponds. N. marliacea chromatella can be planted with up to 120cm of water above the crown.

Water Arum or Arum Lily, Zantedeschia aethiopica:

a well-known local species; it does best in a marshy sink at the edge of the pond.

Bulrush Typha capensis:

typical bulrush with the brown, club-shaped flowering section. Does well in marshy areas and shallow pots. Has no colour, so won't compete aesthetically with the fish.

Iris sp, Iridacea

Rhizomed and tuberous perennial flowering plants; grow in dry or wet places. One of the only flowering plants often found in authentic Japanese water gardens.

Water Arum Cyperus antiquorum:

does well in moist ground, marshy conditions or shallow water.


Be aware that the commonly found floating species such as Water Hyacinth and Water Lettuce are declared weeds and it is illegal to have any in / on your pond.



De Kock, S, and Watt, R, 2003: Living Jewels, Jonathan Ball Publishers, Johannesburg.

James, B, 1986: A fish keeper's guide to koi, Salamander Books, London.

Rees, Y, et al, 1989: The Practical Encyclopaedia of Koi, Salamander Books, London.

Sterba, G, 1983: The Aquarist's Encyclopaedia, Blanford Press, Dorset.

Tamadachi, M, 1990: The Cult of the Koi, T.F.H Publications, NJ, USA.