#1. Make sure all plants stay underwater with at least 2" of water over the soil line. This insures that the rootstocks will not freeze, killing the hardiest of aquatic plants. Above ground ponds are subject to freezing deeper than 2" at the surface. Try at least 4" of water over the soil line.
#2. Waterlillies are safest since they are at maximum depth. Removal of dying dormant foliage is only maintenance required. Tropical lilies have their best chance of surviving the winter when placed in the warmest spot in the pond. Typically the warmest spot is the deepest spot, assuming no circulation is present. Circulation can bring the cold water to the top of the pond and push the warmer, deep water away.
#3. Plants that emerge out of the water like cattails, grasses and broadleaf bog plants should be trimmed back so their stems extend out of the water 1-2 inches. Trimming them below the water level tends to drown them. Remember to trim them only after they have been placed in a location where the soil line stays at least 2" under water. Tropical bog plants can be placed in deeper (warmer) water and then trimmed. Bog plants like Iris that do not go very dormant in the Atlanta area should not be trimmed but allowed to grow as they please.
#4. Floating plants, like hyacinths and water lettuce, are target to freeze first. In some cases the hyacinth will overwinter but rebound very slowly the next year. Use your own discretion. What you will want to avoid is a lot of dead foliage dying and rotting in the pond.
#5. Dead foliage in an earthen pond is a welcome addition as a compostable source to enhance organic makeup. In a lined pond there is a lack of soil to carry the proper bacteria to compost such additions since majority of plants are grown in their containers. Without a soil bottom there will be a lack of habitat for beneficial bacteria and organic toxins will form. Of course, as any pond owner knows, falling leaves are usually the largest source of organic debris in a pond and offer a greater threat in most ponds.