I was told by a local pond expert that I can overwinter my hardy plants on the plant shelf (shelf is 12" deep and in zone 5). I was also told that I can overwinter my fish while the pond ices over as long as the water is fairly deep (36") and clean and kept free of leaves with a net.

I have planned to close my pond this way. Sounds too easy but it sure does simplify things!

You should add aeration to your pond, or at the very least, put a thermo pond heater in to keep a hole in the ice for the gasses to escape when it ices over. What is your pond volume and how many fish do you have?

700 gals with four fantails about 4 inches each.

Get on down, KK! You go girl!

A gal that knows, whos already got 10' of snow, and a nearly snow covered fish house.

Some hardy plants can stand their roots freezing such as water iris. Others will turn to mush like pickerel weed. In Zone 5, there will be ice in the roots of plants on a foot deep shelf during the coldest part of the winter. That will kill some hardy marginals but not others.

As far as the fish go, they need two main things over the winter. First, they can't freeze solid. Contrary to what a few people have claimed, if a goldfish freezes solid, it's dead. I've had a few do that. Second, there needs to be gas exchange. That means oxygen in and carbon dioxide, methane, and hydrogen sulfide out. The last two are toxic gases produced during the decomposition of organics (dead plants and animals and waste). That's why it's better to have a clean pond going into winter without a lot of debris. You can keep a hole in the ice using an air stone, small pump, de-icer, etc. See http://www.fishpondinfo.com/winter.htm for more on winterizing ponds.

Fantails are more sensitive to low temperatures and temperature fluctuations. They can take down to freezing like single-tailed goldfish but are more apt to die over the winter. Predators also catch fantails more easily than they do single-tailed goldfish.

I had also heard of an alternate but foolproof way to overwinter plants.
This method would have you place the drained pots in a basement or other cold location that will be maintained above freezing, inside a closed plastic bag with the pots covered with wet burlap.

My first thought is that they might grow mold??

The plants would have to be kept wet, cool (between 34 and 50 degrees F), and have ventilation through them. I also would worry about mold and rot.

As long as they are Hardy Plants then you can cut the follage back to about a inch above the pot, but you should drop them to the deeper part of your pond so the roots dont freeze. For the size of your pond i would just get a floating heater to keep a hole open in the ice