Mr Edwards, 56 and his wife Anna, 40, called in enthusiasts from Wrexham Heritage Society when he lost his keys on land at Oak Farm in Bronington, near Whitchurch.
But as well as finding his keys – which had gone through a lawn mower – the team armed with metal detectors also found 14 mediaeval coins dated from the 14th and 15th centuries.
At an inquest in Ruthin the North East Wales Coroner John Gittins declared the coins – from the reigns of Edward III, Henry V and Henry VI – as treasure.
Mr Edwards said: "It is a once in a lifetime thing.
"It is such a shock, you just can't quite believe it.
"You realise those coins were there before they ever found America or anything.
"You just can't believe you're holding something that is 600 and something years old.
"We only bought the land three years ago and nothing like this has ever been found before."
He said he was "hoping for an unexpected windfall" but does not know how much the coins are worth.
They were found to contain about 90 per cent silver and the most recent of them was relatively unworn.
It is thought Wrexham County Borough Museum is interested in acquiring the coins which, because of their age and metal content, should be classed as treasure trove.
Any proceeds will be split between Mr Edwards and Cliff Massey, 83, the metal detecting enthusiast who made the find.