Aquatic plants have similar requirements as their land relatives (zones, sun, etc.). However, there are a number of other factors that are unique to pond plants such as water depth, chemical makeup and stillness.
Common Plant Requirements: Most plants are either annuals or perennials. Annuals last one season and will need to be replaced next season. Perennials live through multiple seasons. Most plants need x-amount of sun (full, partial, shade, etc.). This will depend not only on where you live, but your water feature’s locale (close to a building – perhaps your pond is always shaded). Zones are the average temps of the country with lows and high averaged in. Ensure that a plant’s hardiness can endure the extremes. Just like sun, the water feature’s locale could vary from the zone for better or worse. For instance, perhaps the pond is in a sheltered area, up against a hardscape wall facing south. Or, perhaps it’s on a windswept hill. Other tags may include growth, average size, fertilizer, spacing, pruning and bloom info.
Water Gardens: Some people install a water feature for the sake of aquatic plants. If you are trying to add a variety of pond plants, ensure you plan the shape of your banks to accommodate the varying levels of water depth needs. Bog plants like their feet wet but nothing else. Ensure you have a shallow liner area which may only have an inch or so of water at the extreme edges of your feature. Marginals like the top of the pot submerged (~6” deep). Deep marginals may be placed up to 16” deep. Water lilies, deep aquatic plants or submerged oxygenating plants that grow on the bottom can be placed deeper (2 to 4 feet deep). Note: pot in soil but cover the top with pea gravel, rocks or planting medium (granular clay). Of course, there are floating plants that live on the water surface (no soil needed). Be aware though that too many surface plants will block sunlight for plants below. Plan your garden carefully.
Water Conditions: Just like animals, aquatic plants like the chemical make-up of your water to be within a certain range. Thankfully, their range is nearly in-step with optimum pond water range for ion and nitrates (oxygen is not considered and plants add O2 to the water!). Ensure the plant you are considering does not have a chemical need that would greatly differ from your pond. Another requirement on some plants is how turbulent the water is. Some plants, like lilies and bog plants, do better in still water. Most plants need fertilizers; and blooming plants may require additional. Some fertilizers are added directly into the water, but many are tabs that you push into the potted plant soil (this is generally preferred) as general fertilizers contain nitrogen, phosphorous and potassium. It is better to target a single plant with an aquatic fertilizer tab rather than altering your overall water’s chemical makeup. More plants mean more oxygen and fewer nitrates (NO3). Remember; remove dead growth or plants from the pond as they add ammonia.
Algae, Invasive and Noxious Weeds: Just because we are talking about aquatic plants doesn’t mean you can’t have weeds! Animals such as ducks visiting your pond pass aquatic plant seeds from other bodies of water to yours. Seeds, wind or accidental planting (in the soil of other pond plants) can also introduce unexpected and unwanted plants. Weed killers specific to specific intruders are available. Algae in balance with the pond are not bad as it is a green plant that gives off oxygen. However, an imbalance of water conditions (like too much phosphorous) can cause massive algae blooms choking out or even growing on your pond plants. Remember, pond plants compete for the same resources as algae does, so more pond plants can mean less algae. Some perennials may become too successful and become invasive competing with other pond plants. If so, each season (or as needed) cut back, divide, or trim roots to check it. Note: Most states and local jurisdictions have a list of Noxious Weeds. Aquatic plants are VERY difficult to control. Always check that you are not planting one. If you have one, remove it and ensure to dispose of it properly.
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