During the fall and early winter, water gardening focuses on preparing for shutting down your pond. Many people close their pond for the coldest winter months, and then reopen in the spring when the ice melts. Your winter aquatic plant care will depend on where you live and how cold it gets during the winter. If the pond won’t be subject to freezing temperatures and frost, you can continue business as normal. Overwintering pond plants makes spring reopening easier, and keeps your plants and pond healthy. Water quality can be disrupted if plants die and breakdown in the water. Repurchasing all new plants in the spring can be expensive when many aquatic pond plants can survive the winter with a little help.
Aquatic plants vary in hardiness and can handle cold up to a certain temperature. Pond plants you see in the store are not always native to your area. Tropical plants originated in warm climates with very mild winters, so they cannot survive freezing temperatures and need to be moved indoors. Hardy submerged plants like anacharis and sweetflag can handle the cold water, as long as they are moved deeper, where the water doesn’t freeze all of the way through.
Proper winter pond plant care helps with water clarity and spring reopening. Tropical and floating plants cannot survive freezing temperatures. If they are left in the pond, they will sink to the bottom of the water and slowly begin to decay. The beneficial bacteria are not as active in cold temperatures, so the plant parts are not broken down efficiently. The excess nutrients can harm pond life and lead to an algae bloom in the spring when the weather warms.
Each plant is labeled according to the USDA Plant Hardiness Zone Map, which uses average temperatures in your area to determine which plants are best suited for your climate. If you have plants that can not handle your winter temperatures, you will need to move them to a warmer place indoors or compost and repurchase in the spring.
Hardy marginals typically live in a pot, submerged in the pond water, and have leaves or flowers above the surface. After the first frost, many of the leaves and flowers will turn brown. You can remove the dead foliage and trim so there is only about two inches of stem above the waterline. It is important that the roots and crown do not freeze during the winter. You can place them near a de-icer to prevent the stems from getting frozen in the ice.
Tropical Marginals can either be treated as annuals or moved indoors to a warm place with lots of sunlight for the duration of winter. Alternatively, a grow light can be used for 12 to 14 hours a day. Tropical marginals must be moved inside before the first frost. Tropical marginals make great house plants during the winter. They do not need to be stored in water, just kept damp. Wait until warm spring (when the water is consistently 70°F) to replant the tropical marginals outside.
Bulb tropical marginals like Taro and Canna require a little extra care. Allow the bulb to dry out and then cut back the foliage and stem. Store it in damp soil or sand until replanting in the spring.
Plants that stay submerged in the water are typically are very hardy. They should be trimmed back between 4 and 2 inches and placed in the deeper water. Submerged plants will survive as long as they do not get frozen in the ice. They will be happy in the deepest part of the pond, where the water is the warmest.
Floating plants are often very delicate, and will die once the surface water freezes. Many are less expensive than the other pond plants, and can be easily repurchased in the spring. If you decide to overwinter floating plants, you need to store them in water and keep them in a warm area. You can keep them in your home or in an aquarium with a heater to keep the water temperature warm.
Tropical lilies require extra special care during the winter. Before the first freeze, take your lilies (pot and all) and place them somewhere where they can dry out for about a month. The lily will turn into a little tuber, around the size of a walnut. Place the tuber in a jar or bag with damp peat moss and store in your refrigerator. Check to make sure it does not get too dry during the winter. When the weather warms in late March or early April, remove the tuber from the peat moss and place in a small container of water on a windowsill that receives a lot of sunlight. Small roots will begin to grow, and you can remove the lilies from their tubers and place in pots. The pots need to be submerged in water, just a few inches. Once the pond water is consistently above 70°F, then the lilies can be replanted in the pond.
Many of your pond plants will make it through the winter, ready for spring, with a little bit of help. Your aquatic plants may need to be moved to a different spot in the water, or moved inside all together. Begin planning and winterizing your plants before the first frost hits, if possible. Tropical plants will not be able to handle cold temperatures, and will die if they are not moved inside before the freeze. Taking care of your pond plants in the winter will help them stay healthy so they can flourish in the spring.