How to Prevent Koi Up-Rooting Plants in a Garden Pond
Question ... Are plants and Koi a good mix? Is there any way I can prevent my Koi from rooting around in the planting baskets in my pond?
Answer ... You have partly answered the question in the question. I could say: IF you prevent your Koi from rooting around in the planting baskets then you can say that Koi and plants in a pond are a good mix! Koi are naturally curious and are equipped to grub around in mud and soil; they are strong enough to tip over even large aquatic baskets and have a playful nature that loves swoop in and around plants particularly at mating times.
Koi like all other pond fish are likely to benefit hugely from the natural balance in the watery environment that a full quota of plants undeniably brings. Also the daytime oxygenating from submerged aquatics is another of the main benefits. The uptake of unwanted chemicals by all water plants, particularly nitrates, is one benefits that comes naturally with plants but is difficult to achieve with anything but the most sophisticated biological filtration equipment.
However for many serious Koi keepers leaving water management and oxygenation to nature is to tempt fate and lose the control they feel is essential for their precious charges. Therefore they are quite happy investing serious money on filtration and oxygenation in a serious hobby.
There are other Koi keepers who claim to have had no problems with have plants in the same environment. This may be because they have particularly big pools or well-established ponds, or they introduced the fish when they were very small when their impact on their environment would have been less noticeable.
If you are beginning and your pool is already constructed you can try planting your plants in aquatic baskets as normal, but even if you use the fine-meshed Finofoil baskets, line the basket with some underlay material or a hessian square to keep the fine silt in the basket even if it pounded by Koi noses below the water line. Use a heavy, chemically inert gravel (20mm minimum) on the surface of the baskets. Start oxygenating plants and lilies off in a quarantine area, perhaps blanked off with concrete blocks or boulders. This is the basis of a compromise design for a pool designed for Anglo Aquarium plant at the Hampton Court Flower Show in 2002 by Amanda Broughton. It was called The Royal Balinese Retreat and displayed an exotic mix of plants and fish. The fish were huge Koi and were kept separate from the plants by an invisible underwater barrier that was merely a black painted block-work wall rising from the depths to near to the surface.
Alternatively consider a vegetable filter or reed bed system, so that plants can do the job you need them to do without hindrance from the fish.