Water plants are not much different than garden plants, in that they need the correct placement for sun or shade, need to be fertilized and must receive special care throughout the winter. The most common pond plants are hardy and tropical water lilies and lotus plants. Time and scope of maintenance will be determined by the size of the pond, the presence of fish and whether a filtration system is needed to keep the ecosystem balanced.
Hardy plants can be placed in the pond when all threats of frost are over. They can be left in the pond all winter if dropped to a 12- to 14-inch depth where they will be well under the ice level. Tropical plants should not be placed in the water until the water temperature reaches 70 degrees Fahrenheit. If they are placed too soon, they will go dormant and delay the growing season by up to six weeks. While planting or repotting, keep the plants moist and out of direct sunlight, because they dry out rather easily.
To keep algae growth down, 60 percent to 70 percent of the water surface should be covered with plants. This is especially important if you have fish in the pond or if you are not using a filtration system.
Use slow-release water plant fertilizer tablets to keep the soil full of nutrients for your plants. Water plants are heavy feeders, but because many fertilizers will cause algae to grow in the pond, the specialized water plant tablets are best. Place one in the container when first potting the plant and another each month until mid-fall. At that point you will want the plant to start to go dormant.
Be very careful when fertilizing your lawn that the fertilizer does not leach into the pond. Building an edging around the pond will help to keep the lawn fertilizer out of the water.
Just like other garden plants, water plants need to be kept tidy. Cut off any dead leaves or flower heads as soon as you notice them. You should also pull the containers up once or twice a season to make sure there are no dead roots sticking out of the container that need to be trimmed off. While you have the container out, check the gravel or stones on top and replace them if they've been washed off. This will keep the soil where it belongs and keep fish, if you have any, from eating the roots of the plant.
Many ponds contain fish, and once in a while a fish will die. These dead fish should be removed from the pond as soon as they are noticed to keep bacteria and fungus from growing and contaminating the plants. Algae can also be a problem if leaves are not skimmed from the pond daily during the fall or if the filtration system is not cleaned and maintained properly. Keeping the pond tidy will ensure healthy, long-lived plants.
Tropical plants require a little more maintenance throughout the winter than hardy plants. Tropicals should be kept indoors at an average of 70 degrees F with plenty of light. An easy way to do this is to keep them in an aquarium. Otherwise, repot them into smaller containers with drain holes. Keep them in a sunny window or under grow lights with the container in a pan of water. Never allow any water plant to dry out.
Hardy plants can be left in the water if there is room to drop them down so the growing tips do not come in contact with frozen water. If that isn't possible, they should be covered with a plastic bag and kept in a basement or garage that gets no warmer than 50 degrees F or colder than 40 degrees F. You will need to keep a close eye on the plants to make sure the soil does not dry out. The plastic bag will hold in most of the moisture; however, they should be watered occasionally to protect them.