With the shorter days and cooler weather comes a change in foliage. For trees, we get to enjoy the vibrant fall colors that remind us of apple picking, pumpkin patches, and playing in the leaves. However, the same does not happen for our water plants. Colors begin to fade and leaves begin to dry out as they prepare for the winter ahead. As we have mentioned in previous blogs about preparing your pond for fall, executing seasonal pond maintenance is important, but paying attention to autumn aquatic plant care is also prudent. Savor the rest of the water gardening season by providing the extra attention needed to properly winterize your plants.
Become aware of your hardiness zone
Check plant hardiness zones to determine which zone you live in and which plants are hardy to your particular zone. Plant hardiness zones indicate the geographic restrictions of a particular plant, often based on temperature lows during winter. While many plants do well in summer, irrespective of zone hardiness, non-hardy plants cannot live through a winter outside their specific zone without special care. If a plant is able to survive the winter in your distinct zone, that plant is considered "hardy" to your zone.
Bog/marginal, hardy water lilies, and lotus plants are considered hardy. These aquatic plants can be kept in your pond but when the temperatures begin to drop and they start turning yellow and brown, this is a signal to stop fertilizing them as they prepare for winter dormancy. Be sure to trim the dying foliage of your marginal plants down to 2” above the water level. Remove dead or decaying material so it does not make its way into your pond. Rotting plant material can compromise water quality and the safety of aquatic life. However, several strategically selected plants, such as cattails and semi evergreen varieties, can be left untrimmed to add aesthetic during winter. If you have a deep-water garden that will not freeze solid, hardy water lilies and lotus can be left in the water, as long as you sink them to deeper water for the duration of the winter. However, if you have a small or shallow water garden that freezes solid, they will need to be brought indoors for dormant storage, much like non-hardy marginal plants.
Similar to the marginal plants in your pond, the foliage of your lotus plants will need to be trimmed back after they have died and turned brown. Be careful not to cut the leaves while they are still green because the freshly cut, hollow stems are vulnerable to disease, which can spread to the plant’s tuber, possibly killing the plant. Lotus tubers will not withstand freezing, so any plants that are growing in the shallow areas of your pond should also be moved to deeper shelves, away from freezing water.
Non-Hardy and Tropical Plants
In warm climates, tropical marginals will keep growing and will require fertilizer as usual. Plants of tropical origins, including many floating and submerged plants, will not survive the harsh winters of the northern United States. Water gardeners who live in these areas will need to treat these plants as annuals by replacing them each season. These plants need to be brought indoors for the winter since these plants are very sensitive to cold. Saving just a few floating and submerged plants is sufficient since you can replant them in spring and these fast-growing plants can repopulate themselves easily. Aquariums or large containers, such as a children's pool or Tupperware container, are great for housing these plants. A cool decorative alternative is to treat them as tropical houseplants. Most tropical marginals will do well potted in heavy garden soil in a sealed clay pot with no drainage holes, while larger containers can hold multiple plants. When kept wet, the plants do well in a sunny window or sunroom but it is recommended to provide bright, supplemental lighting (a grow light or plant light) and heated water (at least 70°F) to over-winter successfully. Do not fertilize these plants during this period. Keeping tropical water lilies indoors over the winter is difficult so it is advised to treat them as annuals and purchase a new plant each season.
Taro and Canna are tubers, which can be left to dry out and go dormant without water and light in a frost-free area, such as a basement. Drape a damp piece of burlap or newspaper over the top of the pot to retain moisture. The darkness allows the plant to go dormant and prevents the plant from sprouting prematurely. Check the container periodically throughout the winter to make sure the potting material stays slightly moist.
Be proactive and take the time now to properly care for your aquatic plants. This will mean happier and healthier plants next spring, and a cleaner pond environment, which is better for your aquatic life.