Know your onions in the garden...

Just as Simon Cowell knows his music, and Bake Off judge Paul Hollywood knows his cakes, so award-winning gardenerJim Buttress knows his onions.

And his melons, aubergines, carrots, radish and runner beans.

The plain-speaking horticulturalist, former Royal gardener and current RHS Britain in Bloom judge is now also judge in BBC2’s new six-part series The Big Allotment Challenge, and he pulls no punches judging harvests produced by contestants on their made-for-TV allotments

Filmed in a Victorian walled garden on the Mapledurham Estate in Oxfordshire, nine pairs of keen gardeners have spent months planning, planting and nurturing.

Given their own greenhouses, they were handed particular vegetables, fruit and flowers to grow, as well as facing a number of additional weekly challenges including flower arranging and chutney-making.

This was judged by floral arrangement expert Jonathan Moseley and preserves specialist Thane Price.

The series, presented by Fern Britton, was filmed last year from early spring until late summer, when award-winning Buttress then judged the produce, from blemish-free radishes to perfect sweet peas.

So how harsh was he with this judging?

“I was once nicknamed Judge Dread but you don’t have to be hard, as long as you’re fair and consistent.’’