Retention ponds thrive when planted and tend to experience issues when kept bare. Unless the pond will be cleaned and fully drained on a seasonal basis, it should be planted wherever possible both in the water and around the edges of the banks. It’s not always possible to plant on the banks themselves if rock or concrete armoring is required to allow for access without erosion. However, plants are one of the best erosion and water quality tools, even for fully-lined retention ponds. These living additions go far beyond just helping the water feature look natural and blend into the landscape. Here’s what you need to know about selecting the right plants and where to add them to any type of retention pond design.
Types of Water Plants
For a healthy ecosystem, each retention pond should include a combination of all of the main types of water plants. The four categories of aquatic plants are:
- Free-floating, the top layer of growth that don’t put down any roots and move around on the surface. Examples include water hyacinths, duckweed, and water lettuce.
- Emergent, where roots or tubers are buried in the sediment under the water and the leaves and other parts extend far above the surface. Arrowheads and cattails are two of the most well-known examples.
- Floating-leaved, which appear like free-floating due to their leaves on the surface, but have roots anchored in the sediment as well. This category overlaps with emergent plants, but common examples are lotuses, frogbit, and water lilies that have foliage floating on the surface.
- Submerged, the rare plants that grow completely submerged and prefer not to extend above the water. Most of these plants are tropical and therefore largely limited to aquariums, but some outdoor options include hornwort and fanwort.
Vegetation for the Banks and Watershed
It’s not enough to add water plants to the pond and ignore the ground around the pond. All the surfaces that slope towards the pond to direct runoff in its direction are considered part of its watershed. Watershed vegetation plays an essential role in controlling erosion, runoff, and water contamination levels. If the soil is left bare leading up to the edges of the banks, large amounts of silt will end up filling the pond and shortening the wait between dredging. Fertilizing the turf around a pond increases the amount of nutrients in the water, resulting in algae growth and other issues. Using healthy turf adapted to the area reduces the need for fertilizer, resulting in well-vegetated and erosion-resistant watersheds without contaminant issues.
Controlling Nutrient Flows
Speaking of avoiding fertilizer around the retention pond, keeping the watershed area properly planted is part of the process of controlling nutrient levels in the water. Without turf and other grasses on the slopes leading into the pond, it’s all too easy for fertilizer runoff from other sources to accumulate in the pond. High nutrient levels trigger algae blooms that are hard to control, affecting the visual appeal of the pond and harming any fish or other life that might be in it. Well-planted turf zones and barriers of edge plants can make a big difference in how the nutrients are absorbed before the water ever reaches the pond.
Removing Invasive Plants
Keeping invasive plants out of the pond is a key maintenance practice to keeping the retention pond attractive. First, many plants that tend to move into open water edges are unattractive and messy looking; such as phragmites. Second, letting the desired plant species get replaced by cattails or other fast spreading plants also reduces the designed water treatment capacity of the pond. If the pond is designed to improve water quality for eventual discharge, it’s important to routinely remove the seedlings or saplings of invasive weeds that move in. Even ponds that hold water indefinitely need to maintain the right balance of plants to stay visually appealing.
Creating Artificial Wetlands
For the most advanced water treatment options and attractive appearance at the same time, consider surrounding the pond’s inlet area with an entire constructed wetlands environment. This includes patches of plants like cattails that might be too aggressive to use in other parts of the pond. Water that flows through the wetlands will need to linger whenever possible to let the bacteria colonizing the roots of the emergent plants do their work at purifying the water. Building a wetlands area will require additional maintenance to keep the plants in appropriate balance for water treatment, but the resulting water quality improvements could allow for safe discharge to the environment or just a more attractive holding pond.
Pairing Plants with Flexible Pond Liners
There’s no need to choose between a well-planted and natural-looking retention pond and a flexible liner. Impermeable liners made of the right reinforced material can be installed under layers of sand, gravel, and soil without concerns about tearing. This allows for the construction of an artificial base for direct planting no matter the design of the retention pond. If exposed liner installation is desired for other reasons, plants can still be added around the edges of the banks and in the pond with the help of sunken planters and containers. There’s no need to cover the entire base of the pond in soil just to add plants around the shelves to help absorb nutrients as runoff flows in.
Even existing retention ponds, that are completely bare, are easily planted after being updated with new liners from BTL Liners. Choose the right material for your project by picking one of our fish-safe and plant-safe products that is ideal for a naturalized design.
