Facts About Aquatic Invasive Species and Water Gardens

A water garden is fundamentally an outdoor aquarium. The gardener needs to manage the pH, nutrients, and organisms introduced into the system.
Facts About Aquatic Invasive Species and Water Gardens - Articles


Just because a plant or animal is invasive doesn't mean it can't be ordered and delivered to your door or purchased locally. Unwelcome hitchhikers may also accompany your purchase. Plants and animals known to be invasive or prohibited in the state are often part of plant orders in the water or plant medium or even used for packing.

It is recommended that you rinse plants in a light colored bucket of clear tap water until they are clean before planting and dispose of any packing materials or water shipped with the plants carefully. Watch for animals or other plant fragments. If it seems likely that the plant has hitchhikers, you can clean emergent types of plants such as arrowhead (Saggitaria spp.). Dip the plant in a 10% chlorine solution, swish it around and shake it off. Rinse in tap water after 30 seconds. This should not be used on submerged plants like elodea (Elodea canadensis).

Any hardy non-native plant or animal species may become the next problematic invasive species. In addition, many closely related (same genus) plants can hybridize with the native species, often passing on aggressive traits.

When selecting plants, consider using species native to the region or, if you use exotic plants, be careful manage them carefully and dispose of them properly. Never use any invasive plant unless it is well outside its hardiness zone. Pennsylvania ranges in hardiness zones from 5a at its coldest to 7b.

Choose a reputable nursery, ask if the vendor is aware of regional or federal restrictions and verify the scientific names are correct. Common names may be used for several different species, not all of which are harmless. Garden centers will sometimes give the genus but not the species.

Fish and Snails

Snails, by their nature, are generally easily moved or move themselves under moist conditions. They are often intermediate hosts for parasites. Snails have a large appetite for vegetation that we don't necessarily want eaten. For this reason their use in water gardens is not recommended.

Fish are sometimes added to water gardens for visual interest. Keep in mind that they will add nutrients to the system that you will have to remove with filters or balance using plants. The fish commonly used in water gardens are goldfish and koi, both of which are carp from Asia. As such, they should never be released or allowed to escape. They consume water plants, and can make the water cloudy as they feed. Carp will also grow quite large, sometimes outgrowing their space.

"If you build it, they will come…"

Fish may also be an attractant to birds that consider that expensive koi a tasty snack and can move those snails on plant material or in their digestive systems. Local amphibians such as frogs, toads or salamanders may decide your water garden is a good place to reproduce or hang out. Fish are competitors that eat their eggs. Local turtles may also move in to your water feature and birds and butterflies will come for a drink. Rather than investing in exotic animals, rely on the locals to move in.

Best Management Practices for Water Gardens

  • When siting your water garden, consider proximity to natural water bodies or storm drains that might connect to them. Flooding events can cause the release of plants and animals.
  • Be sure your nutrients are in balance and your filters working - any plant will get out of hand if over-fertilized.
  • Plan your garden - Be sure what is going in and around the garden is native or can be controlled. Seeds may spread into the wild even if the plant seems well behaved in the garden.
  • If you do want non-native plants, be sure they are not considered noxious and be very careful to manage them.
  • Know where your plants are coming from and that they are properly identified. Ask at your local plant supplier if they are aware of state and federal restrictions. Be particularly careful of mail-order materials.
  • Clean and inspect everything before placing it in the water garden. Plants should be rinsed in clean tap water in a light colored vessel so you can see they are clean. Especially 'dirty' plants can be rinsed in a chlorine dip.
  • Avoid snails. They are very easily spread by moving themselves or being picked up by wildlife. Some can even pass through the gut of birds without damage when eaten.

This information was generated through a collaboration between Penn State Extension and the Mid-Atlantic Panel on Aquatic Invasive Species.