Water hyacinth (Eichhornia crassipes) is a free-floating aquatic plant originating in tropical and subtropical regions. This plant thrives in warm conditions, with an optimal growing temperature range between 68°F and 80°F. Water hyacinths are not tolerant of cold and cannot survive the winter in most outdoor ponds, requiring indoor relocation to prevent freezing. Exposure to temperatures below 35°F (2°C) or sustained water temperatures below 50°F (10°C) causes plant tissue damage and eventual death. Successfully overwintering these plants demands careful preparation and a controlled indoor environment to maintain stock for the following season.
Preparing Water Hyacinths for Winter Storage
The process of preparing water hyacinths for indoor storage should begin well before the first anticipated frost. Plants should be removed from the pond when the water temperature consistently drops below 50°F (10°C), as growth slows considerably at that point. When selecting plants to save, choose the smallest and healthiest specimens. These are easier to manage and have a higher survival rate than larger, older mats.
Once removed, thoroughly rinse each plant to remove algae, pond debris, and aquatic pests like snails that could be introduced indoors. Trimming the plants is also beneficial, which involves removing any long, dead, or yellowing roots and leaves. This step reduces the overall biomass, minimizing the risk of rot and disease during storage.
Choosing the Right Overwintering Method
The two main strategies for indoor survival involve either maintaining the plants in a state of semi-dormancy or encouraging active growth throughout the winter months. The choice between these methods depends largely on the gardener’s available space, light, and commitment level.
Semi-Dormant/Moist Storage
The semi-dormant method is suitable when space or equipment for a full aquatic setup is limited. Select a container without drainage holes and line it with a damp, sterile medium such as sand, peat moss, or potting soil. Place the plants directly onto this moist substrate, allowing their roots to settle into the media rather than floating fully in water.
Store the container in a cool, dark location, such as a basement or unheated garage, where the temperature remains stable between 40°F and 50°F (4°C to 10°C). Keep the media moist but not waterlogged to prevent rotting during this reduced metabolic state. The plants may appear to die back, but small dormant buds or crowns can survive to sprout again in the spring.
Active Growth/Aquarium Storage
To maintain active growth, water hyacinths must be kept in a heated aquarium or water-filled container indoors. This method requires warmer water temperatures, ideally kept between 60°F and 75°F (15°C to 24°C), often necessitating the use of an aquarium heater. Unlike the dormant method, these plants require intense, consistent light to photosynthesize and remain green.
Strong artificial lighting, such as a high-output grow light, must be suspended above the plants and run for at least 12 hours a day to compensate for the weak winter sun. Even with supplemental light, the plants frequently become “leggy” and pale, a sign of etiolation due to insufficient light intensity compared to summer sunlight. This technique is higher maintenance, requiring regular water topping and small amounts of fertilizer to sustain growth.
Reintroducing Plants in the Spring
Do not move the water hyacinths outside until all danger of frost has passed and the pond water temperature is consistently above 60°F (15°C). Moving them out prematurely risks cold shock and death.
The plants must be gradually acclimated to full outdoor sun exposure over several days. Place them in a shaded spot first, then move them to partial sun before their final placement in full sun. This process helps prevent the leaves from suffering sunburn. Once floating freely in the pond, the warmth and natural nutrient load will encourage rapid reproduction, quickly replenishing the pond’s surface with new growth.