He had placed the bombs throughout Christchurch and a man needed two hearing aids after suffering hearing damage when one bottle exploded.
He told the court he wanted to apologise to the court and community.
"It was a foolish, insensitive act, and I regret it – I really do."
Coombs' lawyer said his cleint had been watching prank videos on YouTube before he recorded footage of himself pretending to cough on fellow shoppers at the Barrington Fresh Choice.
Judge Jane McMeeken said he owed the country an apology, describing the incident as serious – and this wasn't an isolated incident.
He sparked outrage over the weekend when he filmed himself coughing and sneezing on customers in the Barrington Fresh Choice and posted it on Facebook.
He later took down the video and apologised, claiming he'd had too much to drink.
Police arrested Coombs on Saturday night.
McMeeken told the court she considered this serious offending – which had caused concern nationwide.
In the video, Coombs walks through Fresh Choice supermarket in Barrington, coughing near other customers and smiling.