It is true that Japanese koi eat plants. When the water temperature is above 70° F koi have an enormous appetite. Since koi do not have a stomach they don't eat very much at one time. They are naturally bottom feeders and constantly sift through the bottom rubble for food. Having a gravel bottom will give them a natural place to forage instead of destroying the plants.

When planting hardy lilies take them out of the pot and rinse the roots. Plant them directly in the gravel and make sure the roots are well covered. Put fertilizer pellets in the gravel to give them a good start. The roots will spread under the gravel wider than the canopy and will add to the biological filter. They will bloom more without ever having to fertilize again.

When planting tropical lilies, it is best to leave them in their pots, since they will have to be removed at the end of the growing season. Be sure to wait until the water temperature stays consistently above 70° Fahrenheit before planting in the spring. If planted when the water temperature is to cool it can cause shock and the plant may not survive. Add fertilizer pellets when planting and on a regular basis to promote propper growth and blooming. At the end of the growing season skip the lilies's last fertilization. When it starts loosing its leaves, usually when the water temperature falls below 65° Fahrenheit, remove the potted plant from the pond. To store over the winter you have to understand that tropical lilies never experience cold or even cool weather in the zones where they originate. They do experience dry seasons, where the lake beds dry up and trigger the plant to go into a dormant state. Simply remove the potted plant, cut away all the foliage including buds, and place in a dark space at room temperature. The soil will dry out slowly mimicking the dry season that the plant would naturally experience. In the sprimg when the water temperature is above 70° Fahrenheit the lilly can be replanted in the pond.

Watercress is, in my opinion, the best plant for a koi pond for two reasons. It makes a natural plant food for the koi. Watercress contains significant amounts of iron, calcium and folic acid, in addition to vitamins A and C, and koi love it. This plant really starts growing when the appetite of koi kicks into high gear, easily keeping pace. It also has a dense root mat that does an excellent job of filtering the water. Plant in a shallow high current flow area to one side to keep to koi from destroying it before it gets started in the spring. In the fall after the first frost cut back to a small area.

Floating water hyacinth can result in the koi eating the roots. I usually plant in the shallow stream just below the waterfall. Their roots bury deep in the gravel to provide excellent filtration. They tend to grow taller and bloom less. Mine have grown 3 foot tall and extend 12 feet down the stream and seem to benefit from the splashing of the waterfall. This is another plant that will have to be pulled in the fall. Pickerel Rush is another plant that enjoys the splashing from a waterfall. I use them to hide the liner below the waterfall and they have bloomed constantly all season.

Marsh Betony has narrow rough edged leaves with small pink to purple orchid like flowers. They can be invasive and should be planted in a low current semi-contained area to naturalize. Water mint is another plant that can become invasive. Both of these plants are very hardy and do well in sun or shade blooming all summer long.