Why pond plants escape
Water gardens are small, but water is connected. Floating fragments, seeds and runners can wash or be carried by birds, flooding or careless disposal into streams, ditches and lakes. Aquatic invaders can be especially hard to control because they grow fast, break into fragments that each regrow, and can form mats that crowd out native plants and reduce oxygen for fish and other life.
Regulations on aquatic plants vary a great deal by state and province, and some species are prohibited from sale or transport. Check local rules before buying. For the broader definitions behind these terms, see invasive vs aggressive plants.
Pond plants to avoid
Whether a plant is a problem depends on your climate and region. Tender tropical plants may die back in cold winters but still cause trouble in warm regions.
Floating plants
- Water hyacinth (Eichhornia crassipes): a notorious invader of warm waterways, regulated in many places.
- Water lettuce (Pistia stratiotes): forms floating mats in warm regions.
- European frog-bit (Hydrocharis morsus-ranae): spreads in northern lakes and wetlands and is regulated in some areas.
- Duckweed and watermeal: several species are native and harmless in moderation, but they can cover a pond surface quickly (see below).
Submerged plants
- Hydrilla (Hydrilla verticillata), fanwort (Cabomba caroliniana), Eurasian watermilfoil (Myriophyllum spicatum) and curly-leaf pondweed (Potamogeton crispus) are classic invasive pond and lake weeds that spread by fragments.
- Parrot’s feather (Myriophyllum aquaticum): a popular water garden plant that spreads aggressively and is restricted in some areas.
Marginal and bog plants
- Yellow flag iris (Iris pseudacorus): non-native, spreads by seed and rhizome, and is invasive in many wetlands.
- Purple loosestrife (Lythrum salicaria): invasive in North American wetlands.
- Creeping Jenny (Lysimachia nummularia) and water forget-me-not (Myosotis scorpioides): often sold for pond edges but can spread beyond the garden.
- Taro (Colocasia esculenta): can be a concern in warm regions.
- Cattails (Typha spp.): several are native, but they can spread vigorously and take over small ponds. Some forms and hybrids are considered aggressive in wetlands.
Native alternatives
Choose plants native to your region, and check with a local native plant nursery or extension office. Examples used widely in eastern North America include:
- Blue flag iris (Iris versicolor) in place of yellow flag iris.
- Pickerelweed (Pontederia cordata), native in eastern North America, though it can spread vigorously in a small pond and may be a problem outside its native range.
- Arrowhead (Sagittaria latifolia) for muddy margins.
- Fragrant white water lily (Nymphaea odorata) and spatterdock (Nuphar spp.) for floating leaves and shade.
- Marsh marigold (Caltha palustris), swamp milkweed (Asclepias incarnata) and soft rush (Juncus effusus) for the damp edge.
- Coontail (Ceratophyllum demersum) as a native submerged oxygenator in many areas.
Native ranges vary, so verify a species is native where you live. A pond ringed with natives also supports pollinators and amphibians, much as the plants in an upland border would. Tall moisture-lovers such as Joe Pye weed also suit damp pond margins.
What plants will goldfish not destroy?
Goldfish and koi tend to nibble or uproot soft, tender plants. Tougher options often mentioned include water lilies and plants grown in pots with gravel on top so fish cannot dig them out. Results vary with fish size and stocking levels, so treat any list as a starting point. Whatever you choose, keep ornamental fish in closed ponds that cannot overflow into natural waterways.
Will duckweed take over a pond?
It can. Duckweed multiplies quickly in still, nutrient-rich water and can cover the surface in warm months. Native duckweeds also feed waterfowl and shelter small animals, so the aim is balance rather than elimination. Skimming it off with a net, reducing nutrient inputs and adding shade from lily pads can help. Dispose of removed plants away from water.
What is the hardest pond plant to get rid of?
Submerged weeds that spread by fragments, such as hydrilla and Eurasian watermilfoil, are among the hardest because cutting can multiply them. Rhizome-forming plants such as yellow flag iris and cattails are also persistent. Control methods depend on pond size and local regulations; for a larger pond, talk with a licensed aquatic professional or extension service before using herbicides or machinery.
Containment and disposal
- Grow aggressive aquatic plants in pots or baskets within the pond, not in open soil.
- Never dump pond plants, water or fish into natural waterways, storm drains or ditches.
- Dry removed plants on dry land or bag them for the trash according to local guidance.
- Clean boots, nets and equipment after working in or near natural water.
- Ask sellers where the plants came from and whether any restrictions apply.