Gardeners have been warned their potting mix or compost could be deadly if they don't take precautions after a spate of people catching legionnaires' disease in Canterbury.
One person has died and another 10 people have been hospitalised in Christchurch in November from legionnaires' disease, which authorities believe was caught from potting mix or compost.
Canterbury medical officer of health Alistair Humphrey says the disease seems to have come from a variety of sources and not just one batch of potting mix.
"It looks as if it's been a warm spring, people have got out into the garden, and sadly they've used potting mix and got unwell from it," he told Radio New Zealand.
Dr Humphrey said it was an avoidable disease if people took the right precautions.
These included opening bags of potting mix outside while wearing a mask and gloves, to do so with a pair of scissors, and to dampen it down so dust doesn't fly around.
"We don't want to discourage people from gardening," he said.
"It's perfectly simple to reduce your risk by taking all these precautions when you're handling potting mix, or indeed your own compost from your compost heap because that also grows legionella."
Dr Humphrey says most of the people affected were elderly, as is usually the case with legionnaires' disease, though it was more serious if people smoked or had a pre-existing respiratory illness.
All but one of the 10 people who contracted the disease from potting mix or compost has been discharged.
One other person contracted the disease from a different source.