Water lilies are aquatic perennial plants known for their floating pads and striking blooms that grace the surface of ponds and water gardens. These plants are rooted in the sediment at the bottom of the water body. However, the common assumption that they need rich, traditional garden soil is inaccurate and can lead to significant problems. Water lilies do need a substrate to anchor their expansive root systems, but the composition of this “soil” must be very specific to avoid compromising water quality.
The Specific Substrate Water Lilies Need
Water lilies require a heavy, dense medium, often referred to as aquatic soil or a clay-based loam, to serve primarily as an anchor. This substrate must be heavy enough to remain firmly at the bottom of a container without floating or dispersing into the water column. The density of the clay or loam holds the substantial rhizomes of the plant securely in place, preventing them from being disturbed by water movement or fish activity.
Avoid using light, fluffy materials like standard potting soil, compost, or mixtures containing high levels of organic matter such as peat or manure. These lighter materials will float out of the planting container and cause the pond water to become cloudy. Furthermore, organic matter decomposition releases excessive nutrients, particularly nitrogen and phosphorus, directly into the water. This nutrient overload feeds undesirable algae, potentially leading to a widespread bloom. The ideal medium is a simple, heavy topsoil or a commercially available aquatic compost formulated to be dense and low in organic content.
Practical Planting Methods and Containers
The most common and effective method for growing water lilies in lined ponds involves planting them inside containers before submerging them. Specialized aquatic baskets, which often have mesh sides, are frequently used because they allow water to pass through freely while containing the heavy substrate. Alternatively, solid, non-perforated containers, like heavy-duty plastic pots, can be used to completely isolate the substrate from the pond water. Choosing a large container, ideally 10 to 14 inches in diameter, is recommended because water lilies are vigorous growers and need ample space for their roots to develop.
To plant a water lily, the container is first filled with the heavy clay or loam substrate, leaving a few inches of space at the top. The rhizome is positioned horizontally or at a slight angle, ensuring the growing tip remains exposed at the soil surface. The roots are gently spread and covered with the substrate, which is then lightly compressed to eliminate air pockets and secure the plant. A final layer of washed pea gravel or coarse sand is placed over the top of the soil, acting as a crucial cap to prevent the finer substrate particles from mixing with the water and causing turbidity. After planting, the container should be slowly lowered into the pond to prevent the disturbance of the substrate.
How Aquatic Plants Acquire Nutrients
Water lilies are known as heavy feeders, meaning they require a substantial amount of nutrition to produce their large leaves and prolific blooms throughout the growing season. Water lilies draw the majority of their required nutrients from the concentrated substrate around their roots, unlike terrestrial plants that rely on the richness of the surrounding soil. The dense clay substrate provides physical stability and acts as a reservoir for supplemental feeding.
For optimal flowering, press slow-release aquatic fertilizer tablets directly into the substrate near the root zone, typically on a monthly basis during the active growing period. These specially formulated tablets dissolve slowly within the compact soil, providing a steady supply of nutrients, particularly phosphorus, which is essential for flower production. The plant’s roots absorb these localized nutrients, preventing them from dissolving into the main body of the pond where they could promote algae growth. Water lilies also play a secondary role in water quality by absorbing some excess nutrients, such as nitrogen and phosphorus, directly from the water column through a process known as phytoremediation.