These submerged plants are called "oxygenators" because they add oxygen to the water garden during the day and absorb carbon dioxide during the night. Nutrient-rich water in full sun is the perfect situation for algae growth. As a purifier, the submerged plants compete with algae by removing unwanted and excess nutrients from the water, which helps prevent algae build up.
Oxygenating plants have very weak stems that can’t support themselves; therefore, spend their lives completely under the water’s surface. Instead of getting their nutrients through their roots in the soil, they get them directly through their leaves. Although most of these plants grow completely under water, some have flower stalks that rise above the water surface.
Usually, submerged plants are sold in bunches; a good way to decide how many bunches to buy is to get about one bunch for every square foot of water. When placing them into the water garden, the stems can be pushed into gravel or deep into soil. The other option is to just let them float free in the water. All of these plants are easily propagated by taking 8-12 inch cuttings from the new growth during the summer.
Submerged Plant Species
- Parrot’s Feather (Myriophyllum aquaticum) – The fernish foliage grows mostly submerged, but may be partially emergent. Some species have flower spikes that poke an inch or so above the water in the summer.
- Water Violet (Hottonia palustris) – This is actually a member of the primrose family. Its leaves are stemless and pale pink-lilac flower spikes rise above the water in the spring.
- Starwort (Callitriche spp.) – Fish enjoy nibbling on this tangled mass of leaves. The summer flowers are small and white, and the foliage underwater is sparse. The leaves on top of the water form thick mats.
- Fanwort (Cabomba caroliniana) – Fanwort is also a fish favorite and they often use this as a food source in the cold months. The swirls of leaves are perfect hiding places for fish, as well. The summer flowers are white with yellow centers and small.
- Willow Moss (Fontinalis antipyretica) – This plant is slow growing and prefers water that is slowly moving and is clear. It serves as a great place for fish to spawn as the eggs easily stick to the Willow Moss’ leaves.
- Water Thyme (Egeria densa) – This is one to grow in areas where it will not survive the winter. If it does too well, it becomes a noxious weed. Its flowers bloom in the summer and are three-petaled and white.
- Canadian Pondweed (Elodea canadensis) – This is another plant to watch for as far as a possible pest. Care needs to be taken that it doesn’t get into natural waterways or streams; it’s incredibly invasive. It does have tiny, late summer flowers.
- Hornwort (Ceratophyllum demersum) – This plant sinks to the bottom of the pond in the winter. It’s a good choice as an oxygenator because algae has a hard time competing with it.
- Yellow Water Buttercup (Rannunculus flabellaris) – The Water Buttercup is beautiful in large colonies especially while in bloom during the spring and summer. This North American native is not an invasive plant and it grows either submerged or floating.
- Underwater Arrowhead (Sagittaria natans) – This plant is great for algae control. It does bear a single white flower in shallow water levels and is one of the first submerged plants to grow in the spring.
- Curled Pondweed (Potamogeton crispus) – This plant may be invasive if allowed to wander. Stems are up to 6 feet long and have white flowers that poke just above the water surface.
Because every water garden has its own water habitat dictated by the garden area, plant life, sun situation and water depth, not all of the plants in the submerged group will survive in every pond. A few varieties may have to be tried before the right one is found for that particular garden.
Chris McLaughlin - Chris McLaughlin's gardening books include "The Complete Idiot's Guide to Heirloom Vegetables." Check out her complete profile.
