Inspector Montalbano, BBC4, Saturday How to Grow a Planet, BBC2, Tuesday

Minutes into the new detective series Inspector Montalbano, it was clear that if you had tuned in expecting the finely-wrought Euro-drama that has become BBC4's Saturday night strong suit (Borgen, The Killing, Spiral), you would be disappointed.

The opening titles were promising – sweeping shots of Ragusa, Sicily, a chaotic maze of buildings buttressing bright blue sea, suggesting a sunny port with a shady underbelly.

It was Montalbano himself that made the heart sink. As he rolled grumpily out of bed and into the office, snapping at buffoonish flunkies and dodging calls from his girlfriend, his caricature, sorry, character – and the entire production – began to look a bit noir-by-numbers. Against the backdrop of contemporary thrillers and their diverse male and female leads, a bloke with a five o'clock shadow and the odd snappy one-liner looks quaint at best.

With two murders to solve – a businessman with a knife in his back and a Tunisian fisherman gunned down at sea – Montalbano dutifully spent the remaining hour and a half bombing about the island in his Fiat, pausing occasionally to interview formidable siciliani, eat pasta and have evasive chats about marriage with the girlfriend.

There was a vaguely political dimension – the fisherman turned out to be some sort of terrorist mastermind, but that remained very hazy, strangely so, given that the script was big on exposition elsewhere. By the time the credits rolled, Montalbano had solved the murders, held corrupt authorities to account, proposed to his girlfriend and, in a particularly ludicrous strand, adopted a Tunisian orphan along the way.

It's hard not to conclude that were Montalbano in English it would never have found its way on to BBC4. Subtitles aside, this is Midsomer Murders stuff (albeit with a Mediterranean sensibility; I'm pretty sure I never saw DI Barnaby's other half sitting in bed topless).

It doesn't help that the first film in this prestigious new slot – a couple of episodes have been aired in odd corners before – was made in 1999, long enough to date it, but not to turn it into a period piece. Perhaps when we get to some episodes made more recently things will pick up – the series and the novels by Andrea Camilleri on which it's based are huge in Italy, where it's still running.

The high expectation/low return formula was reversed over on BBC2, where twinkly-eyed Scottish geologist Professor Iain Stewart is on a mission to change the way we think about plants with How to Grow a Planet. "People think plants are passive, static, unresponsive," he lamented, articulating exactly why I embarked on this programme with a sense of educational duty rather than enthusiasm.

"Nature" may be a popular subject among viewers, but for most that extends only to animals, vast expanses of snow and pyroclastic flows. Plants don't usually get much of a look in, but here Stewart did a sterling job championing their vital role in the earth's creation.

Aided by quite a budget, he skipped between continents, seeking out landscapes that revealed something of what the plant kingdom was up to millions of years ago, from African lakes, similar to those in which plants – or their bacterial forebears – first converted sunlight into oxygen, to fossilised forests in Canada.

There were the set pieces that are now the familiar stuff of the science documentary: CGI recreated ancient, super-sized insects; dramatic aerial shots of 90-metre sequoia trees; an interactive experiment (Stewart spent 48 hours in a glass box with 300 plants for company –and oxygen). But it was the old-fashioned time-lapse photography that made the most impact, the creeping of tendrils and unfurling of leaves highlighting the limits of human perception.

Stewart's cheerleading was infectious; I found myself quite indignant on behalf of the underrated plant kingdom. We owe it our lives, after all. And, of course, plants are terribly useful in absorbing the carbon dioxide that results from flying round the world to make a TV series.