They bought a 1ha swampy area back from a neighbour, and turned it into the Te Punanga Ripo wetland in 2004. It's now a nursery for eels, Sr Noelene said, and the eels have to leave it to get to sea and breed.
"Some of the staff have seen old female eels heading across our drive down to the river."
Some of the Sisters' hillside is already taken up with one of the City Mission's gardens, and about 80 fruit trees. Much of the rest is very steep.
Sr Noelene has had Whanganui plant ecologist Colin Ogle there, to make a list of suitable trees. She wants some for bird and bee forage, and all will store carbon, slow the pace of rainwater and hold on to the hillside soil.
Species are likely to include ngaio, pittosporums and matai. She's hoping they will shade out the kikuyu grass growing there, and stop it spreading.
Much of the work will be done by part-time employee Shane Dean, who helps with the planning. The Corrections Department's community workers will do any heavy jobs.
The project is in line with Pope Francis' views on "integral ecology", and Sr Noelene is part of a group of sisters investigating the true meaning of kaitiakitanga with tangata whenua.
"It's the local understanding of love of the Earth and relationship with the Earth," she said.