This article was published in The Fringe, May 2013

New Zealand Milfoil

Ponds, lakes and stormwater reservoirs are all in need of plants to maintain healthy, clean water. The plants can act as filters for suspended sediment, and can absorb excess nutrients from the water ensuring any water released is purified as it continues its journey to the sea. 

Of course some water plants can grow too well, and many imported exotic species have become weeds with the resultant clogging of waterways and de-oxygenation of the water making it poisonous for wildlife. 

Balance is required and nature has determined that the species local to an area are the best for it, no matter that we might think otherwise! 

When restoring habitats, we must think holistically and include all the elements that nature would have had before mankind interfered. Start with the plants and the fauna will follow. 

Fortunately there is an amazing range of plant species designed for a life submerged in ponds. The five native Myriophyllum species (milfoil) are among the most useful to recreate habitat and cleanse water. They all are excellent plants for ponds, slow-flowing streams or fish tanks. 

There are, however, three closely-related exotic species which are banned as unwanted organisms under the National Pest Plant Accord. Therefore it is unwise to collect milfoil from the wild as there is a high probability it will be a pest. The worst is Myriophyllum aquaticum or 'Parrot's feather' which is a wide-spread weed, choking waterways and often moving as a floating raft from one area to another, frequently attached to boats. 

The native species range in size from the small Myriophyllum  votschii, growing 3 -7cm tall as a bottom-dwelling groundcover forming tight cushions, to the largest M. robustum which can be an emergent standing up out of the water. It is a rare northern endemic which unfortunately looks very like the weedy Parrot's feather.

Myriophyllum peduculatum is also low growing, less than 10cm tall, with short creeping stems. It prefers damp ground or shallow water forming semi-aquatic swards. The plants establish from either seed or vegetative growth which can be free-floating, greatly enhancing its distribution. It occurs throughout New Zealand.

Perhaps the two most vigorous and common species are Myriophyllum propinquum and M. triphyllum which both occur throughout New Zealand. Plants can grow in both ponds and streams to 2-3m tall in water up to 3m deep, and in summer they emerge above the water level. Both species survive dry conditions during which they reduce to prostrate herbs. These milfoils can be propagated by seed or vegetatively from fragments and rhizomes.

If you have an aquarium, a pond, or water in need of cleansing, try growing our naturally-occurring native aquatics, starting with the native milfoils. The environment will thank you for it.