Will Algae Harm a Waterlily?

Types

• Numerous species of algae can arise in a water garden, but most often it's free-floating algae that cloud the water and turn it green. These algae prosper in sunny, warm water that is rich in dissolved minerals already present in the water, or that build up in the pond from the wastes of fish or amphibians. Hair or filament algae grow into threadlike, cottony masses in water and can be more problematic. Pond slime coats submerged items in a water garden.

Algae as Indicator

• When new water is added to a pond or a new water garden is stocked with fresh plants and fish, the water's quality and chemical balance is out of whack. For the first two to six weeks, the pond undergoes a transformation as the sun warms the water, and water nutrients and animal excrement change the water's pH and levels of nitrates. As an ecosystem, the pond naturally goes through growing pains as plants establish and absorb nutrients, shade and cool the water and the chemicals and pH gradually come back into balance. Alga prospers when the chemical composition and pH of the water isn't stable. Some algae will always exist in a water garden, but excessive algal growth, known as a bloom, can create a stagnant, green and unattractive water feature.

Effects on Waterlilies

• Waterlilies absorb nutrients from the water through their soil-bound roots as well as their stems and leaf undersides. Algae and slime may coat the leaf stems and any emerging leaves from the rhizome atop the soil, but once leaves unfurl and lay atop the water surface, algae is no longer an issue. The lily pads bask in sunlight and make food for the plant. As long as algae does not block light to the photosynthesizing lily pads, there is minimal, if any, disruption.

Concerns

• The health and performance of waterlilies can deteriorate if the water is plagued with excessive algae for a long time. After the initial greening of water from algae during the chemical imbalance in a new pond, the amount of algae subsides to tolerable levels. If the water remains dense, translucent green for weeks, it can prevent light from reaching the waterlily's rhizome and disrupt the development of newly emerging leaves. If a thicket of stringy algae rests atop the rhizome, the newly emerging leaves may not reach the surface.

Tips

• The more leaves a waterlily or other aquatic plant has, the more shading occurs on the water surface. Without light and warmth, algae declines. Lily pads cool the water and rob the light needed for algae to grow so fast and dense to create a green gooey mess. Rainwater, which lacks nutrients, is the best addition to a water garden. Tap or well water contains fresh mineral salts that can increase the amount of algae. Shade or cool the pond water with more vegetation before considering any chemical pesticide such as an algaecide. Adding chemicals can harm wildlife and the widespread killing of algae results in a rapid change in water nutrient and pH conditions, which can lead to more problems.