Farmers' markets are struggling to cope with a dearth of produce and rocketing prices following the wet summer and a harvest hampered by torrential downpours.

The harvest would usually be well under way by now, but it has been delayed by up to three weeks in Scotland. In addition, much of what has been retrieved from the sodden fields has not been suitable for sale.

The potato harvest is the worst since the 1950s and Grant Montgomery, who runs the Ardardan Farm Shop in Cardoss, near Helensburgh, said produce prices were being pushed up.

He said: "The market price for potatoes is a lot dearer than it was last year. We buy ours from the farm next door, but the ground has been so wet that the guys haven't been able to get in and get them out.

"There's been a lot of waste, a lot of stuff has rotted from lying in damp ground. We're just at the start of the harvest now, but there's going to be a shortage later on. We've just been telling people to hold off buying big bags of potatoes because they're probably going to go bad."

Other crops have also been affected. Mr Montgomery went on: "Cauliflowers were costing money that you couldn't buy them at. Broccoli was the same – the guys just can't get into the fields to harvest them.

"Supermarkets can bring in vegetables from further afield, but we buy all our produce locally."

Gordon Caldwell, a vegetable farmer at Dowhill Farm in Girvan, sells produce at the Kilmacolm farmers' market in Inverclyde on the first Saturday of every month.

He said harvesting had been particularly difficult this year.

"The bad weather we've had already means that things are growing more slowly," said Mr Caldwell.

"There's obviously a pressure on prices. As the yields go down you've still got to cover the same costs per acre, but at the same time you don't want to alienate customers.

"Cauliflowers are pretty tight right now, but I do try to look after the customers who've been loyal to me."

Allan Bowie, vice president of NFU Scotland, described this year's harvest as unprecedented: "My father has been farming since the 1950s and it will have been the worst he has seen.

"I went through 1985 and we thought that was bad. A lot of people just want to get through this year and look forward to next."

Mr Bowie described a split in fortunes across the country. He added: "North of Aberdeenshire they haven't had it easy, but they've had a better harvest. South of Aberdeen, where you would expect things to be easier, it has been extremely difficult. The whole east coast, Stirling, Ayrshire, Dumfries and Galloway, the west of Scotland, has had too much rain.

"The islands have actually had a good summer. Something has happened with the weather pattern. It has obviously shifted."

Mr Bowie farms potatoes, wheat and barley near St Andrews, where he says there has been 70% more rain this summer than normal.

"We are still trying to lift potatoes. What we have lifted, the yield is a good 40% to 50% down, just because of too much rain and lack of sunlight.

"Talking to other potato growers, that seems to be the norm."

While conditions have led to price increases this year, the repercussions of the harvest will last longer.

"Normally we would expect to get next year's wheat crop in after the potatoes are lifted," Mr Bowie continued. "I don't think that will be the case this time around."

Any crops that have been planted for next year, including winter barley, oil seed rape and wheat, will suffer from the excess rain in the last fortnight, he says. In addition, it will take years for the soil structure to rectify itself after being saturated.