Aquatic Plants
Various
Pond and container-water plants, sorted by the job they do rather than by how they look.
Three jobs
Submerged oxygenators (hornwort, anacharis, vallisneria) keep the water clear by competing with algae for nutrients. Floating plants (water lily, water lettuce, frogbit) shade the surface and starve algae of light. Marginals (pickerel rush, iris, arrowhead, sweet flag) plant the shallow edge and take up nutrients. A pond that only has the pretty floating layer will fight algae forever.
Cover about sixty percent of the surface
That is the working target for shade. Below it, algae get the light they need; much above it and you lose the open water and the oxygen exchange. Lily pads and floaters together usually get you there by midsummer, so plant for it rather than to it in spring.
Use loam, never potting mix
Peat and bark float straight out of the basket and foul the water. Heavy garden loam or dedicated aquatic soil, topped with an inch of pea gravel to hold it down and keep fish from stirring it up, is correct.
Planting depth by type
Marginals sit with one to six inches of water over the crown - use bricks or upturned pots to set the height. Hardy water lilies want twelve to twenty-four inches over the crown; tropicals slightly shallower. Submerged oxygenators go on the bottom, weighted or bunched. Getting depth wrong is the usual reason a plant sulks.
Feed with tablets
Granular fertiliser dissolves into the water column and feeds algae instead of your plants. Push aquatic fertiliser tablets into the root zone every four to six weeks through the growing season, and stop in autumn.
Divide every two or three years
Water lilies and most marginals become congested, stop flowering and push soil out of the basket. Lift in spring, cut the rhizome into pieces with a growing point each, and repot in fresh loam. This is the main routine maintenance job.
Overwintering
Hardy lilies and marginals survive if their crowns sit below the ice line - move baskets to the deepest part of the pond in late autumn. Tropicals must come indoors or be treated as annuals. Cut back dead foliage before winter rather than letting it rot in the water, which fouls it under ice.
Algae and water balance
Green water in spring is normal while plants wake up and usually clears on its own by early summer as shade and oxygenators establish. String algae is a nutrient problem - remove it by twisting it onto a stick, and check for overfeeding fish or runoff entering the pond. Barley straw, added early, helps.
Be careful what you release
Several popular water plants - water hyacinth, water lettuce, parrot feather, hydrilla - are aggressive invasives in waterways and are restricted or banned in some states. Check before buying. Never dump surplus plants, old pond water, or fish into a stream, lake or storm drain; compost surplus plants on dry land instead.
- Categories
- Submerged, floating, marginal
- Light
- Most want 6 hrs+
- Container
- Aquatic baskets + heavy loam
- Feeding
- Tablets, not granular
- Winter
- Sink hardy types below ice line