Aquatic plants are a significant component of a healthy pond ecosystem, maintaining water quality and providing habitat year-round. When cold weather arrives, the ability of a plant to survive winter depends on its natural hardiness. Preparation involves protecting the plant’s root structure from freezing solid by utilizing the pond’s deepest, most insulated areas. Correct preparation ensures plants return to full vigor when temperatures rise again.
Categorizing Hardy Pond Plants
Hardy aquatic plants withstand cold temperatures and ice by entering a dormant state. This group is divided into categories based on their growing location within the pond environment. Their survival depends on keeping the rhizomes or root crowns from freezing solid, which is achieved by placing them below the expected ice line.
Hardy Marginals
Marginal plants grow in the shallow, muddy edges of the pond, and their survival depends on their roots staying submerged in unfrozen water. Common examples include Cattails, various species of Iris, and Pickerel Weed. The root crowns of these plants must be relocated to a deeper section of the pond, typically 18 to 30 inches, to prevent ice from penetrating their growing point.
Hardy Submerged/Oxygenators
Submerged plants, also known as oxygenators, remain active or dormant entirely underwater. Many species are naturally cold-hardy and continue to release oxygen, which benefits fish and aquatic life under a layer of ice. Examples include Anacharis (Waterweed) and Hornwort, which tolerate low water temperatures. These plants remain at the bottom of the pond through winter without special relocation, provided the pond does not freeze completely solid.
Hardy Water Lilies
Hardy water lilies are distinct from their tropical counterparts, which cannot survive freezing temperatures. These hardy varieties (Nymphaea species) prepare for winter by drawing energy back into their thick, buried rhizomes. They require a long, cold rest period to resume growth in the spring. The rhizomes must be situated deep enough in the pond water to prevent them from freezing or drying out during the coldest months.
Preparing Plants for Winter Dormancy
Preparing pond plants for winter dormancy begins as the water temperature consistently drops and foliage starts to die back naturally. The primary goal is to prevent decaying plant material from fouling the water and to protect the root structure from ice penetration. This process involves cleaning and strategic placement adjustments within the pond.
Trimming and cleaning foliage prevents the accumulation of sludge and toxic gas buildup under the ice. Cut back yellowed or dead leaves and stems to within a few inches of the plant’s crown or rhizome. For marginal plants, some foliage can be left standing above the water line to facilitate gas exchange through the ice. Removing decaying matter prevents oxygen consumption and reduces nutrients that could fuel a spring algae bloom.
Adjusting the placement of potted plants is the most critical action for ensuring winter survival. Hardy water lilies and marginals in containers must be moved to the deepest part of the pond, typically a minimum of 18 to 24 inches below the surface. This depth ensures the root crowns remain submerged in water that stays consistently above freezing. The deep water acts as a natural insulator, protecting the plant from damaging freeze-thaw cycles.
Floating plants like Water Hyacinth and Water Lettuce are tropical and must be removed from the pond entirely before the first frost. These non-hardy plants can be composted. For hardy oxygenators, minimal intervention is necessary, as they naturally settle into the pond bottom and remain dormant in the cold water. They should only be trimmed slightly to remove any excess growth before winter sets in.
Spring Transition and Reintroduction
The end of winter dormancy is signaled by consistently warming water temperatures and the disappearance of the ice layer. This is the time to reverse the winterizing steps and prepare the plants for the upcoming growing season. This phase focuses on moving the plants back to their growing positions and performing necessary maintenance to encourage vigorous new growth.
Hardy plants lowered to the pond bottom for winter protection can be moved back to their shallower, summer positions once the threat of a hard freeze has passed. This usually occurs when water temperatures stabilize and remain consistently above 45 to 50 degrees Fahrenheit. Moving them back to their optimal depth allows them to begin absorbing sunlight and nutrients for photosynthesis and new foliage production.
Initial maintenance in the spring involves checking the plants for new growth and performing necessary division. If a plant has become overgrown in its container, it should be divided to prevent crowding, which can stress the plant and reduce blooming. New growth should be visible from the rhizome; plants that show no signs of life may not have survived the cold.
This is also the ideal time for the first application of aquatic fertilizer tablets, especially for heavy feeders like water lilies and lotus. Pressing slow-release fertilizer into the planting medium at the base of the plant provides the necessary nutrients for the renewed growth cycle. Most marginal plants, which pull nutrients directly from the water, do not require this type of fertilization.