The London mayor instead called for a more positive case for the UK staying together.
His criticism of the No campaign follows similar accusations of scaremongering from the SNP.
But a No 10 source said that he "did not recognise" the description of hectoring.
Mr Johnson also said that he was a "huge" supporter of the Union, which he predicted would survive next year's vote.
At a lunch with journalists at Westminster, he said he had a sticker saying 'I heart Scotland' on his car, put there by Strathclyde Police attending the Notting Hill carnival.
"I'm a huge, huge supporter of the union," he said.
"There will be a union in 50 years time, there is absolutely no doubt about that."
But, he added: "If I had some sort of small observation to make at the moment about the campaign to keep the union, it is that we English who heart Scotland should be more emphatic about that and stop playing on the kind of 'You'll regret it if you go' thing.
"I think that I would respond badly to being endlessly warned and hectored.
"If I was told there was value in the Union and that it is wonderful thing I think I'd respond better."
A spokesman for Yes Scotland said: "The fact that even even Boris Johnson is fed up with the No campaign's relentless scare-mongering speaks volumes."