Pond weeds are a common problem in large natural ponds. As ponds mature and age, they often accumulate nutrients (eutrophication) and sludge, which causes excessive growth of plants and / or algae. Each year, the overall growth of both beneficial and unwanted plants increases and can eventually become a problem. Too much plant or algae growth looks unsightly, can cause poor circulation, make it difficult to swim or make the pond difficult to use for recreation.
The first step to solving the problem of unwanted pond weeds is to identify the weed or plant. We have broken the most common pond weeds into 3 categories:
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Although beneficial for ponds, submerged pond plants aren’t considered usually considered very pleasing to the eye. In fact most people refer to them as sea weed, pond weed or some other unflattering name.
Coontail, also known as hornwort, is a dark green, branching aquatic plant that grows submerged in the water. Although it does not have true roots, it does anchor itself to the sediment. In nutrient rich ponds, coontail can grow very rapidly and become a nuisance.
Native to North America, Elodea has small bright green leaves that grow on branching stems. It begins growing very early in the spring in cool water and can be invasive in certain conditions.
Curly-leaf pondweed is an species that was introduced from Eurasia. It is fast growing plant and can grow very quickly, overtaking other pond plants.
Eurasian water-milfoil is a invasive, fast-growing perennial, that will form dense underwater mats. It typical grows shallow water one to three metres deep, but can also root much deeper. Much of the seasons growth tends to die off, in the fall and winter, causing an accumulation of sludge and lower oxygen levels.
Tape Grass (Eelgrass, Wild Celery) grows in shallow water and has long narrow leaves that grow from a cluster at the base of the plant. the leaves grow up to 1 meter long and are only about one centimeter wide. Tape Grass starts growing actively when the water temperature warms up in in the summer months and will divide by sending out runners from the base.
Sago Pondweed (Stuckenia pectinatus) grows in shallow water, and forms dense mats of roots on the bottom of the pond. It has long branching stems and very narrow leaves that taper to a point. It can be fast growing in the right conditions. At first glance, it can be confused with Curly-Leaf Pond Weed.
Emergent / Shoreline plants are one of the most common problem in ponds. Cattails, bullrushes, grasses, irises and phragmites can quickly become established in ponds with shallow shorelines in depths of up to 2 feet. Often, these plants initially colonise new ponds by seeds carried by wind, birds or other animals. Once established, many marginal plants can spread rapidly underground making them difficult to control.
Once established in a pond, floating pond plants such as duckweed or watermeal can grow extremely quickly making the pond look very unpleasant. Duckweed can overtake a pond and completely cover the surface robbing the pond of light and oxygen.
Duckweed is a small free floating plant about 1/8″ to 1/4″ in diameter. Each plant usually has 2 or 3 light green leaves and a few small roots that hang below. Although it does produces seeds, it spreads very quickly in calm, still waters by division. Some fish ans also ducks will eat duckweed, but not usually as as fat as it can grow and replace itself.
Both watermeal and duckweed are pictured above growing together. The duckweed is the larger of the plants, while the watermeal is the smaller plant. Watermeal is very tiny, each plant is about the of a pinhead. Even though both these plants are small, they can reproduce quickly in the right conditions (warm water, lots of nutrients) and completely cover a pond.
Floating-Leaf Pondweed is common in ponds or slow flowing habitats. It produces mainly floating leaves but also has submersed on the same plant as well. The floating leaves are oblong, pointed at the tips, slightly heart-shaped at the base and grow 5 to 10 cm long, and rounded at the base.
Water lilies are slow growing plants that prefer in still, shallow water up to a depth of about 4-5 feet. They help to shade the pond and beneficial habitat for fish and other wildlife. Water lilies have thick tubers rooted securely in the soil, making them difficult to remove. They produce large circular floating leaves that grow up to 12″ in diameter and fragrant flowers up to 8″ in across. Because water lilies are slow growing, It usually takes several years before they need to be trimmed or partially removed.
Spatterdock are similar in many ways to water lilies. They prefer in still, shallow water up to a depth of about 5-6 feet. They help to shade the pond and beneficial habitat for fish and other wildlife. Water lilies have thick tubers rooted securely in the soil, making them difficult to remove. They produce large circular floating leaves that grow up to 12″ in diameter and small yellow cup-shaped flowers about 3″ in across.