This may help you some fishy
Introduction to Water Iris
Iris are hardy marginals. They are some of the easiest to keep pond plants. There are many different kinds of iris. For land iris, there are snow iris, dwarf iris, bearded iris, Siberian iris, and Japanese iris. The pond iris include flag iris and Louisiana iris. A few of the Japanese and Siberian iris and perhaps others can also survive in shallow water. Flag iris are the most aquatic and grow well in ponds. They should be planted in soil topped with pea gravel and set with shallow water over the top. They can also be planted bareroot into gravel if the gravel is exposed to the pond water (stream, holed pots, vegetative filter, bog, etc.). Some species like it just barely wet while the yellow flag iris can go up to a foot deep over the crown once it is established.
The yellow flag iris, Iris pseudacorus, grows so well that it often gets out of control. I repot my iris every two years. Even in a 4 gallon pot, a small bunch of yellow flag iris in two years normally has broken through the plastic pot in a few places and has also jumped the pot (sent runners over the top). I have planted extra yellow flag iris on land in areas that get wet when it rains (but are otherwise completely dry), and it grows there as well. You could almost say it is a weed. This is one plant that could possibly put a hole in a liner if planted over one. It is also one of the plants I have grown from seed. I let the seed pods dry naturally and split open. Then, I stored the dried seeds in a paper cup in a cool area inside over winter. The next spring, by just sprinkling some seeds around, I got a few to sprout. It turns out I did not really want them there. One in the overflow area has grown rather large. I fear it could puncture the liner as it is not potted. After it flowers each year, I cut all the vegetation down but it barely has an effect. The plant's roots are strong so it cannot be pulled. So, I leave it be.
Iris that grow well do not really need fertilizer. Often they jump the pot. Once roots are in the water, they can glean nutrition right from the water.
Blue flag iris, Iris versicolor, and purple iris, Iris tridentata are two other iris that I have. They grow well but not out of control like the yellow flag iris.
Other iris that tolerate being in water are less invasive and easy to control. Some may be rather slow growing and take time to establish themselves. The slower-growing iris are good plants to put in slow-moving streams and vegetative filters (bareroot or in gravel).
Iris should be repotted every two years in the fall. I do that in late September in Zone 6/7. Extra iris can be put back into the pond or planted on land.
Overwintering Hardy Marginals and Iris
Cut all of the dying vegetation as it yellows/browns about an inch or so from the top of the pot. Move remaining pots deeper into the pond if needed so that the plants' roots will not freeze. My pond is large enough so that in Zone 6/7, the marginal area only freezes down a few inches which is not far enough to harm the roots. So, in my case, I do not move the pots deeper. If the pond is too shallow or you do not intend to keep an open area in the ice, you can overwinter hardy plants inside too.
In the fall, I remove yellow and brown vegetation weekly and at some point (after the first frost), cut back whatever remains of the hardy marginals and iris. The iris are the last to be cut as they stay green past the frost.
Most hardy plants can remain in the pond as long as they will not freeze solid. After the leaves have yellowed and been cut off, the pots should be placed so that the roots of the plant will not freeze. In my pond, I can leave them where they are as the ice stays above the pot rim. Each pond is different. In colder areas, the pots may all need to be lowered down deeper or brought inside. Some plants can take their roots freezing including common cattail. To overwinter most hardy plants inside, they can be put in a refrigerator or cold room and kept moist but in the dark. Tuberous plants (hardy water lilies, hardy canna, lotus, etc.) can be partially dried and kept in moist sand. If conditions are not proper, the plants will turn to mush. As I have not overwintered hardy plants indoors, I do not know the details. It is usually easier to overwinter outside. Only if the pond will freeze solid (tub ponds) must hardy plants come inside. Some hardy pond plants (cardinal flower, lizard tail, iris, etc.) can be overwintered buried on land if they cannot stay in the pond. In the case of cardinal flower, it usually dies if overwintered in the pond but not if overwintered on land.
