Ponds and Aquatic Plants

Ponds can create a wonderful feature to be enjoyed all year round and are often a haven for wildlife. However, if they are not cared for properly some pond plants can take over your pond. They can also become established in the wild, where they can smother our native plants, clog our waterways, exacerbate flooding and remove oxygen from the water, which can harm fish.

Pond owners, gardeners, aquarists, anglers and other water users can unknowingly assist the spread of aquatic plants into our countryside. These plants can rapidly become major environmental problems with expensive associated costs.

If you have a pond, always try to:

• Buy your new pond plants bare root. If you buy one potted in soil or compost, wash this off the roots over a bucket and give the whole plant a quick rinse before planting to remove any seeds or unwanted plant fragments.
• Use this, and any other waste water from your pond or aquarium, on your lawn or to water plants in your garden, in areas that are a good distance from waterbodies or drains that flow into them.
• If your pond is near to a wetland or waterbody avoid using any plants which aren’t native to the local area and if any invasive plants appear, remove them before they spread.
• Add unwanted aquatic plants to your home compost or use them as mulch in dry borders, keeping away from waterbodies or drains.
• Protect pond life by leaving any plants you’ve removed on the edge of the pond to drain for a few hours before disposing of them to allow any wildlife to return to the water.
• Pond animals and fish should never be released into the wild either. They may not survive, and if they do they could harm native wildlife.

Avoid invasive species in your pond

Submerged aquatic plants

• Curly waterweed – Lagarosiphon major: has caused major problems in Lough Corrib, Galway as well as at a dam in Dundrum, Co.Down.
• Nuttall’s pondweed – Elodea nuttallii
• New Zealand Pigmyweed – Crassula helmsii: also known as Australian stonecrop it grows in 3 forms – submerged, semi-emergent and emergent. It has caused problems in Lady Dixon Park and Glastry clay pits.
• Brazilian waterweed – Egeria densa: risk assessments have shown this is one to watch – known to be on sale.
• Canadian Pondweed – Elodea canadensis: a widespread long established species which has been present since the mid 19th century. It has mainly settled down in most parts of Ireland but was documented as being highly invasive in the first 50 years following its initial introduction. It is still however known to cause problems in still flowing nutrient rich waterbodies such as disused sections of the Ulster canal.

Emergent aquatic plants

• Parrot’s feather – Myriophyllum aquaticum: has been known to cause problems in ponds.
• Water primrose – Ludwigia peploides and Ludwigia glandiflora: known to be on sale. A slightly warmer climate could benefit these species’. It was recorded recently in ponds in County Kerry. Experience in France and Southern England has shown its potential to be highly invasive.
• New Zealand Pigmyweed – Crassula helmsii: comes in three forms – submerged, semi-emergent and emergent. Has caused problems in Lady Dixon Park and Glastry clay pits and Castlegregory, County Wexford.

Floating aquatic plants

• Floating pennywort – Hydrocotyle ranunculoides
• Fringed waterlily – Nymphoides peltata

Marginal aquatic plants

• American skunk cabbage – Lysichiton americanus: known from a few sites where it can form extensive monocultures around the edges of lakes where it can extend its growth into adjacent wet wooded areas.