Very invasive native with strong, tall, flat, leaves and unusual spiky flower heads. The flowers are borne in spiky spherical heads looking a bit like green conkers.
Top tip: A bit of a thug with roots strong enough to puncture a liner. Excellent for reed beds.
Flowers: insignificant June/August followed by attractive spiky fruits.
Height of plant: 50-100cm from rhyzome.
Propagation: Very easy to divide.
How to plant: For a filter bed, push the rhizome well into the gravel, with 10cms of gravel over the top, or plant into the bank by pushing the rhizome well into the mud secured by weighing down with a brick or large stone.
Recommended planting depth: The planting depth for this plant measured from soil surface to water surface and not including any gravel dressing is 10-30cm.