Hi Steve, In Western Australia, near wetlands (and in them) Z. aethiopica grows. In Winter time it can be found growing in the water. I remember trying to pick some growing in a Winter creek and they must have been at least half a metre down in depth amongst the reeds. It also grows in my Dad's garden but is small and compact there as his soil is mainly sand with some compost. In our local wetlands on the Canning River, where the base of the stems protrude from the ground to the top of the water would be approx.30cm to 3/4 metre in depth. Not sure if this helps. It's a shame it's a weed as the flowers are lovely and many florists are still known to put on their gumboots and trudge through the weeds to get to the flowers! Regards Jacinda Wilson, WA