The 67-year-old from Loughborough in Leicestershire spotted the thieves arriving in a van and watched them begin to steal flowers from his front garden.
Harry Cook's front garden won a Britain in Bloom competition for three consecutive years. Due to its professional appearance, the crooks thought that the garden belonged to the council.
"I could not believe what I was seeing," he said. "There was one man loading some of my pots into the back of a van, while his mate was sitting in the passenger seat as cool as you like.
"I walked over and stood in front of the van. I said to him, 'You're not having them. You can put the blooming things back'.
"There was no way I was going to just stand back and let them steal my flowers and ruin all my hard work. I made it clear they were mine and he was not leaving with them."
The thieves had their eyes on a pot of petunias, two leylandii trees, three conifer trees, a pot of pansies and a large tub of violas, according to The Daily Telegraph.
Cook added: "I was furious, I was holding my garden trowel and I think they both knew I wasn't going to give up my flowers without a hell of a fight.
"It was probably lucky for the van man because my wife Patricia was at Wimbledon watching the tennis but if she had been with me she would have been at my side and they would have had two of us to contend with."
Leicestershire Police spokesperson PC Andy Dixon said: "The victim works very hard to create floral displays in an attempt to raise money for charity.
"We are appealing for anyone with information about the incident or the driver of the grey Vauxhall van to come forward."
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