Two masked men, one armed with an eight-inch knife, the other with a hammer, targeted the garden centre.
They waited until staff arrived to open up, then ambushed them.
Centre manager Nick Thompson was taken at knifepoint to the centre's safe where one of the robbers forced him to open it.
His female colleague was bound with sticky tape and told she would be killed if she did not co-operate.
The incident happened at 8.20am on 10 August.
Thompson told the Bolton News: "They threatened to kill her and forced me at knifepoint to open the safe. Then they got away with the money."
He added: "I was really shocked. We have recently reviewed our security and I was surprised to be confronted by armed thugs on a Monday morning."
The raiders were white, aged in their 20s, wearing dark clothing, balaclavas and gloves. One was around 5ft 7ins tall, the other was of average build.
Anyone with information should call call Bolton CID on 0161 856 5740.
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