Last Updated: 5/5/06

Vegetative Filters
Edible and Medicinal Aquatic Plants
Terrestrial Plants in Ponds

Vegetative Filters

Vegetative filters are those that employ aquatic plants to filter the water of solids and chemicals found in pond water. Plant roots can trap solids while the plant itself takes up ammonia, nitrate, phosphate, and sometimes even toxins. The plant lives off of the ammonia, nitrate, and phosphate and thus helps to keep those chemicals from becoming overly abundant in a balanced pond. Plants used in vegetative filtration should be bare rooted (not in dirt) but may be anchored in gravel or any other porous, non-organic substrate (marbles, rocks, plastic army men, etc.) for those plants that have roots and must remain upright. The anchoring substrate also acts as an additional biological filter where bacteria can grow among the plants' roots. In general, to be most effective, a vegetative filter should cover an area equal to at least 10% of the main pond's surface area. It can be used in conjunction with other filters. Plant-eating animals such as goldfish, koi, turtles, and apple snails should generally not have access to the vegetative filter. Usually, such a filter is at a higher level than the main pond and overflows into the main pond. If a pond is heavily planted, the entire pond acts as a vegetative filter. It is most efficient when most of the pond water is pumped through the filter at least once a day. In my pond, I have a heavily planted waterfall which acts as a vegetative filters. A vegetative filter may be a separate pond, a planted waterfall, the top of a biofilter, a planted stream, or just a header pond where the water is pumped to before falling into the main pond.

Sometimes, floating plants are used for vegetative filtration. Most often, this means tropical water hyacinth and water lettuce. They grow best when it is warm and so can only filter for about four to five months in Zone 6/7. Plants that I have found to be excellent for vegetative filtration due to their intense growth and ability to grow well in gravel include watercress, water celery, mint (in my case aquatic mint always dies but "land" mint likes the shallow water), and parrot feather. Watercress, water celery, and mint can be harvested to eat as well. In some situations, pennywort or water clover may grow fast enough to work as well. All of the above mentioned plants prefer water under about three inches in depth, and they tolerate moderate water flow (moving water). In deeper water (2-6 inches), plants such as yellow flag iris, blue flag iris, cattail, and sweetflag are fast growers that will absorb nutrients and grow in gravel. They can grow too well sometimes overgrowing the area that they have. There are dozens of other possible plants to use. Slower growing plants may grow in vegetative filters but will not extract as much from the water. For your pond, try a number of plants to find out which grows best for your situation.

Edible and Medicinal Aquatic Plants

There are many plants growing in ornamental ponds that can be eaten as food or medicines. In my pond, watercress and water celery grow so well that both the deer and my mother help themselves to handfuls of it to be used in salad or flavorings for almost anything that something in which parsley could be used. Both are somewhat bitter but completely safe to eat.

Other aquatic plants are taken for medicinal purposes. One such plant is pennywort. There are multiple species of pennywort. There used to be a nice article on the internet but the site no longer exists (even in the archives) so I took it out here. Another medicinal plant that will grow in shallow water as well as on land is marsh mallow. For information on how to prepare it for use as a cough suppressant and wound healer, go to this site (this is an archived version as the site is now gone).

Below is a partial list of edible and medicinal aquatic plants. If you have any pertinent information, please contact me. For more information including planting depths, where to buy them, etc., go to the marginal list. Some are not in the lists as they are not usually sold for watergardeners. Many can be found fresh at Asian markets or even regular grocery stores and brought to life and rooted in a container of water.

• Aquatic mint (Mentha aquatica)- leaves; raw or dried; very hardy
  
• Arrowhead (Sagittaria latifolia) - tubers; cooked; very hardy; also called duckpotato (tubers taste like Irish potatoes); lower flowers are female while upper flowers are male; waterfowl love to eat duckpotato, hence the name
  
• Bacopa (Bacopa caroliniana) - lemony leaves; used as a seasoning; also called water hyssop; Zones 7 or higher
  
• Bog cranberries - fruit; raw
  
• Cattail (Typha spp.) - all parts (spring shoots and pollen mostly); many uses; very hardy
  
• Chameleon Plant (Houttuynia cordata) - leaves; use like cilantro.
  
• Duckweed (Lemna minor) - leaves; raw; garnish on salads; hardy.
  
• Flowering rush (Butomus umbellatus) - tubers and seeds
  
• Lemon grass (Cymbopogon citratus) - leaves, tuber; many uses raw and cooked; does not like to be submerged; can buy fresh at Asian markets; Zones 8 or higher
  
• Lotus - tubers and seeds; raw or cooked; many uses
  
• Marsh mallow - roots, flowers, leaves; raw or cooked; medicinal uses such as cough suppressant, immune system booster, and wound healer
  
• Pennywort (Hydrocotyle spp.)- leaves; raw; medicinal for many purposes such as arthritis
  
• Perennial rice (Zizania spp.) - all parts; cooked like rice
  
• Pickerel rush/weed (Pontederia cordata) - young leaves and seeds; raw or cooked
  
• Sensitive plant (Neptunia aquatica and other Neptunia spp.) - shoots; used in stir fry; also called water mimosa; only survives in Zone 9 or higher
  
• Spatterdock (Nuphar luteum) - leaves, seeds, and flowers; raw or cooked; garnishes and salads; hardy.
  
• Sweetflag (Acorus calamus) - rhizomes and young leaves; raw or cooked; many uses; very hardy
  
• Taro (Colocasia spp.) - tubers; boiled, steamed, baked, or fried
  
• Vietnamese cilantro (Polygonum odoratum) - leaves; raw or cooked; may be sold at places that sell herbs; Zone 8 or higher
  
• Water celery (Oenanthe javanica) - all parts; raw or cooked; salads, garnishes, etc.; very hardy; see extensive section above
  
• Water chestnuts (Eleoricharis spp.) - seeds; raw or cooked; used as nuts or made into flour; can buy fresh water chestnuts at Asian stores and plant those
  
• Water spinach (Ipomoea batatus) - leaves; cooked or raw; can buy fresh at Asian markets and root in water; only survives in Zone 10 or higher
  
• Watercress (Nasturtium officinale) - all parts; raw or cooked; salads, garnishes, etc.; very hardy; see extensive section above

One aquatic plant you do NOT want to eat is arrow arum (Peltandra viginica) as it is poisonous.

Edible Aquatic Plant Links:

These links were last verified on 5/5/06.

Incredibly Edible Aquatics - describes how to prepare parts of lotus, water mint, watercress, water celery, and arrowhead to eat.
The Edible Pond and Bog Garden - a UK-based site that lists edible aquatic plants and how to prepare them.
Watercress.com
Wild Silom - that is water celery (this is an archived version as the site no longer exists)
Water Celery
Shady Sweeties - includes pink water celery and chameleon plant

Medicinal Aquatic Plant Links:

Pennywort - article on pennywort as a treatment for arthritis and other ailments (this is an archived version as the site no longer exists)
Marsh Mallow - as a cough suppressant and wound healer (this is an archived version as the site no longer exists).

Terrestrial Plants in Ponds

Many normally terrestrial plants can be grown in ponds. Growing land-based plants in water is called hydroponics. Many plants such as tomatoes are now grow hydroponically. Some land plants can be trained to also grow in shallow, slightly moving water in ponds. Almost anything will grow in a pond if the conditions are right. I have had butterfly bush seedlings (one of the most drought tolerant plant species around) spread all of their roots into my ponds.

One good example of a terrestrial plant in a pond which has recently been made known is impatiens. I have never had much luck with them on land because they shrivel up in the heat, and the deer eat them. In 2001, I put some in my pond's waterfall/stream area. They grew very well, the deer could not reach them, and I never had to water them. Now, some places are selling special plastic troughs in which to plant impatiens and then set them in your pond. The prices are ridiculously high, and you can do it yourself. I just anchored mine in gravel but you can make a trough for them by cutting holes in a solid pot, filling the pot with gravel, and setting it in a shallow area of the pond or anchoring it to the side of a deeper area. Here is a photo of the waterfall on 9/29/01 with impatiens flowering in the water.

Other plants are those that will grow almost equally well in water or on land. Cardinal flower, marsh mallow (related to aquatic hibiscuses), and mint (not aquatic mint but other mints) are some examples. One note on cardinal flower: It is known as both a perennial and a pond marginal. I have found that while it grows very well in the summer in a pond, it often does not survive over the winter. I planted some in my dry garden (which I water daily in warm months) where it easily survives year to year. To overwinter cardinal flower kept in a pond during warm months, it should be removed from the pond and planted into the ground for winter.

In 2002, I had a self-seeded orange pansy come up in the waterfall as well as lots of weeds. I planted another impatien in the waterfall too. All those plants grew so much more vigorously than any plants on land. Almost any plant out there except those that are for deserts can be grown in a waterfall hydroponically! Try it! You might even grow a small vegetable garden.

Update May 2006: The carpet bugle likes growing in my waterfall along with the aquatic plants. Weed grasses like it too. This year, I have impatiens and a cock's comb in floating plant island things growing hydroponically in pond planting media and gravel.

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