Sometimes called frog's buttons or lesser duckweed, common duckweed (Lemna minor) is a fast-growing tiny floating perennial. One of the world's smallest flowering plants, it grows quickly in still freshwater and is hardy in USDA hardiness zones 3 through 8. It provides nutrition to many animals, including fish and birds.
Common duckweed is native to the temperate lands of the Northern Hemisphere, in the northern half of North America and across northern Eurasia. Natural abundance in still freshwater pools, streams and lakes increases where banked with non-alkaline, fertile shorelines.
The tiny plant comprises one round leaf and one dangling, threadlike root that floats on the water surface. Botanically, the leaf is called a frond or thallus. It develops with many air pockets around its vein and leaf cells. It grows rapidly when water temperatures remain above 70 degrees Fahrenheit, and when water cools, the plant submerges as far as the pond bottom to survive when surface ice forms. The insignificant flowers occur in spring, occasionally yielding seeds, but common duckweed multiplies by budding division of its leaves, called turions.
Place duckweed on the still or very slow drifting surface of freshwater in natural water bodies or ornamental ponds or interior aquariums. It tolerates full sun to fully shaded conditions, although growth explodes in more sunny spots because of increased warmth. Hastened growth occurs when water is rich in nutrients, such as nitrogen or phosphorus, the result of farm or lawn fertilizer runoff. Manure from wildlife also contributes to its growth and reproduction.
Common duckweed foliage contains a significant amount of protein and fat, making it a great food source for carp, including goldfish, as well as birds like ducks and heron and the occasional foraging moose, cow or deer. The plant utilizes the nutrients in water, effectively purifying water of nutrient effluent from mature, or fertilizer chemicals. The dense mat-like growth on the water shades and cools the lower depths of the water, discouraging growth of algae.
Place common duckweed in freshwater aquariums, ornamental ponds or natural water bodies to supply carp with food. The plants also cool water temperatures in midsummer, preventing algae. They also help remove nutrients from water to improve its quality. Excess duckweed skims off the water easily for use in making compost or to supply food or plants to additional aquatic areas.