One Canterbury person has died this week and a further 10 have been hospitalised in the region this month from Legionnaires' disease.
All of those affected are believed to have caught the disease from using compost or potting mix while gardening.
A twelfth person has also become sick, from a different type of Legionnaires disease.
The person who died had been using potting mix, said Canterbury medical officer of health Dr Alistair Humphrey, who told Radio New Zealand such avoidable deaths were "terrible tragedies''.
Most of those affected in the region were older, he said.