The balanced pond

Five floating plants to control algae and maintain your water garden's healthy ecosystem.

Credit: Merv Zakus

5 floating plants to control algae and maintain your water garden’s healthy ecosystem

While there are many enjoyable aspects to water gardening, battling that dreaded green water caused by algae formation isn’t one of them. Algae are an integral part of a healthy pond’s ecosystem and shouldn’t be entirely eliminated, however it is important to maintain a balanced pond. Including floating plants in your pond’s ecosystem will help to control algae and maintain water purity.

Here are five floating plants that will compete with algae for nutrients and sunlight, thereby reducing the amount of algae buildup in your pond:

1. Lemna

The most common floating plant is Lemna, of which there are many varieties. Best known is Lemna minor or duckweed, found frequently in the wild and in great abundance, and which can be detrimental to other plants as it robs them of light and nutrients, especially calcium. Fortunately, in a small pond excess Lemna can just be scooped up and placed in compost. Beware of collecting Lemna from the wild as it often carries diseases and pests such as leeches. I recommend purchasing Lemna from a nursery instead. If you do collect from the wild, be sure to disinfect your new plants by immersing them for one to two hours in a solution of four to six tablespoons of potassium permanganate crystals (usually available in pet-supply stores and pharmacies) to 12 gallons of cold water.

2. Azolla caroliniana

Another popular small floater is Azolla caroliniana or fairy moss. This tiny fern features fronds measuring about one centimetre across, which turn a beautiful red and green colour. They are very easy plants to keep over the winter. In the fall, just before frost, place them in a jar, three-quarters filled with water, and set on a windowsill. Reintroduce them into your pond in April.

3. Eichhornia crassipes

Eichhornia or water hyacinth is one of the best plants for removing waste and toxins from your pond. There are two types of Eichhornia crassipes, one larger than the other. I prefer the compact (20- to 25-centimetre) variety, as it looks good in any size pond. Its leaves are dark and shiny with swollen stems, and its late-summer flowers are extremely attractive, featuring strong spikes bearing orchid-like blooms in blue, lavender and yellow. (The plants require a hot summer to bloom.) The fine roots can reach 60 centimetres long and make the best breeding medium for your goldfish or koi, giving the eggs and young fish a secure niche in which to develop.

4. Pistia stratiotes

Easy to recognize, although difficult to grow, is Pistia stratiotes (water lettuce). Its velvety, sessile, parallel-veined leaves reach up to 25 centimetres, giving you a beautiful 50-centimetre-wide lettuce-like plant. I have no problem growing water lettuces in our greenhouses, as they love the permanent moist air about the surface. I have great difficulty, however, growing them in my ponds, as they seem to stop growing there; in fact, they keep getting smaller. Water lettuce likes a water temperature of at least 21˚C. Keep in mind that water drops on the leaves will cause brown spots and eventually deteriorate their tissue.

5. Salvinia cucullata

A northeastern Asian water fern with flat, oval to egg-shaped floating leaves about three to eight centimetres long and covered with fine protective hairs, Salvinia cucullata is well suited for container ponds: It propagates very quickly by the lateral growth of new leaves, which soon cover an area of 20 centimetres.

Past president of both a koi club and a koi and water garden club, Merv Zakus has been building water gardens for more than 15 years.