He said the grass and weeds had encroached across the footpath, making it difficult for two people to walk side-by-side, and awkward for people with pushchairs.
''I wanted to keep the place nice and tidy,'' Mr Johnston said.
''I live in Ettrick and use the footpath regularly and it was just getting worse, so I just decided to do it on my own.
''I like to help the community and it keeps me occupied.''
An invalid beneficiary, he said he worked on the project for a couple of hours a day and had finished earlier this week.
He cleared the footpath from the top of the hill, by the 100km sign, to the Ettrick store on one side - slightly more than 1km - and from the coolstore to the shop on the other.
He also cleared the over-grown grass from under fence lines, as he thought it was a fire hazard.
Mr Johnston said he had many positive comments about the results, including receiving a letter from Central Otago Mayor Tony Lepper, who thanked him for his voluntary efforts. He is so proud of it, he has had eight copies made to show his friends. Mr Johnston intends to plant a small garden using his own plants on the corner of the main road and Moa Flat Rd to keep the area tidy.
And he also regularly picks up rubbish which has been thrown from cars.
But when he is not tidying up, he likes to go fishing.