He thought walnuts would be an economic crop, so he and his father planted six trees on a 6ha site in Dumbarton, between Ettrick and Roxburgh, in 2015.
They planted another 120 last year, and intend to plant more this year.
''I am trying a bunch of different types to see what does the best,'' Mr Diack said.
Each variety has different qualities and harvesting is staggered as each produces at a different time.
''We are not putting all our eggs in one basket.''
He scoped the area to see how well other walnut trees were growing, and also talked to growers in Cromwell before starting the project.
''We could see walnuts grew well in this area and we needed somewhere that was not too far away from Invercargill.
''There is also irrigation and a creek.''
The first trees to be planted have already produced a few walnuts, but he expected that to increase as the trees matured.
Each tree would eventually produce about 50kg annually, depending on conditions.
''It will probably be about four or five years before we start to get a crop off them.
''They are pretty slow-growing, so it is a long-term project.''
In addition, walnut trees liked hard frost and hot summers, so Central Otago was ideal for them.
He eventually hoped to sell the nuts through the family's nurseries or at farmers' markets.
''We will work that out as we go and see what the supply is like.''
If they needed special equipment for the harvest, his father was ''pretty handy with a welder and if we needed something, he can make it up''.
They used grafted trees, which they prepared themselves, sourcing the wood from healthy trees.
-By Yvonne O'Hara