Ben Williams ran over Russell Meech as they helped install 11,000 plants and trees at a private garden in Potters Bar, Hertfordshire, in June 2013.
Hatfield Coroner’s Court heard on Thursday that Meech had a cardiac arrest after the truck which was being used to transport a tree, accidentally ran him over.
Williams horrified, reversed, put the tree down, jumped out and gave CPR to his friend, who he had worked with for more than seven years, the inquest heard.
He told senior coroner Edward Thomas it was an accident. One eyewitness said Meech had tripped in front of the truck and another that he had been walking in a blind spot.
Clarifying Wheeler's recollection of events, senior coroner Edward Thomas said: "Someone shouted 'oh my goodness' and you turned around and Russell was on the ground.
"This all happened very quickly didn't it."
"Yes, it was a split second," Wheeler said. "It was an unfortunate accident and I feel very sorry for Russell's parents and family."