He said getting the call telling him he was in the finals was pretty good, as was getting to go to Auckland with his dad at Easter to film everything.
Joshua is a serious farm boy and his hay-bale launcher invention will be featured on the show.
In his explanation of how it worked Joshua was quoted in local newspaper Central District Times:
"You start this grunty V8 which drives the ram and spins two car wheels [with tyres]. Then you pull a chord to rev the V8 up. Then flick a switch, the ram pushes the bale between the tyres which fires it across the fence into the paddock.
"The best thing is the V8 is fuelled by methane gas from cow poo."
Lets get Inventin' is about science and technology that fires the imagination and encourages children from 9 to 17 to go on the show with drawings and cool ideas.
Joshua said farm life was great and farming was what he would probably do when he's grown up.
"But I wouldn't mind being pilot either," he said.
"I'll have to see."
The ad for the show said the beauty of the programme was some of the country's great inventors bring the kids' ideas to life and that young inventors win their own patents just by appearing on the show.
Being the only boy in a family with three younger sisters was not always easy, Joshua said.
"But they're okay really I suppose."
He and two of his sisters bike 1km every morning to get to the school bus stop.
"Yeah, we're pretty far away in the country. But it's good ... we all like it."
The family live on a 364.2ha sheep and beef property at Pukeokahu,north of Taihape.
"It's a lot of work - but farms are."
Joshua has a pet bull called Ed, now 5.
"He's quite big and not quite as friendly as he was when he was smaller."
His pet lamb, Hayden - who "grew into the fattest lamb you've ever seen" - had now gone to the works, he said.
And living on a farm deep in the country meant that when it snowed there was no school.
"So it means we can stay home and I go out on the farm with my dad."
Once he finishes at St Joseph's at the end of year 8, he'll be off to board at either Palmerston North Boys High or Feilding Agricultural College.
"Yes, I probably be taking science and it will be good to have more choices."
In the meantime, Joshua says he's often drawing ideas for inventions.
"I have a lot of ideas ... on a farm you always need good ideas."