State Fair, Finborough Theatre, London

When Rodgers left Hart for Hammerstein, he traded the settings of Hollywood and Manhattan for the land where the tall corn grows.

In State Fair there's a hymn to that grain, as well as the barley, wheat, and rye of the Midwest. With metaphorical corn in abundance as well, the musical might seem, to switch metaphors in midstream, a fish out of water in today's world. But Thom Southerland has not only mounted a heartfelt, touching revival, he has done so on the handkerchief-size playing area of the Finborough, where he stages a mini-hoedown that raises the roof.

Half the score was written for the enjoyable 1945 film and begins with the bees-buzzin'-'round-the-hive erotic restlessness of the lovely "It Might As Well Be Spring." Thereafter, the quality of music and lyrics takes a dive – that bird "throwing his heart at the sky" in the tired-sounding "It's a Grand Night for Singing" must be related to the lark who, in The Sound of Music, is learning to pray. The little-known songs from other R-and-H shows added for the 1996 stage version are no better, and too many are wistful and muted. Still, "Next Time It Happens", from Pipe Dream, was a happy discovery, as is Laura Main, who, as the betrayed ingenue, sensitively puts across its pain and bewilderment.

Since the story – will a brother and sister find love at the fair? will Ma win the prize for best mincemeat?– is lacking in passion and suspense, much depends on the characterisations, which here are beautifully handled by actors who are believably wholesome. The youthfulness of many of the cast adds to the sense of freshness, though the weathered war correspondent, who declares, "Over a dewy-eyed Juliet/No one has seen me drool yet", seems barely old enough to drive. Except for Main, top honours go to the older folk. Philip Rham and Susan Travers, as Ma and Pa, hold the show together with optimism and serenity, and Anthony Wise, as the curmudgeon in the apple barrel, provides a touch of tartness.

State Fair is set in August, and at the Finborough one never doubts it. But it's worth putting up with the naturalism for a show that dispenses so much good cheer, and even a topical joke: Asked why he's wearing galoshes if the weather report predicted sunshine, a crusty neighbour replies, "That's why I'm wearin' my galoshes!"

To 29 August (0844 847 1652; www.finboroughtheatre.co.uk)