TV

Producers share the secret to a TV show’s longevity

Last week Fox renewed “Bones” for a 10th season, guaranteeing the quirky procedural starring Emily Deschanel and David Boreanaz would live to see its 200th episode — and with no mention of No. 10 being its final go-round.

It’s an unlikely milestone for a show that has endured multiple moves around the schedule and speculation for the past few seasons about its probable end date.

“They always say every year that they expect it to be the last and then they look around and realize the ‘Bones’ audience is actually growing,” executive producer Stephen Nathan tells The Post. “We don’t quite understand it either. A decade seems like an awfully long time. We will be prepared for a series-ender but we will plan on a season-ender.”

On the air since 2005, “Bones” is Fox’s third most-watched drama, averaging 9.1 million viewers behind newer entries “The Following” (11.2 million viewers) and “Sleepy Hollow, ” (11 million viewers).

And it’s hardly the only graying drama refusing to quietly retire. For all the buzz that younger, sexier series like “Scandal” and “The Blacklist” (rightly) generate, an older class of drama veterans is quietly drawing an equal audience after a decade on the air.

CBS’ long-running “NCIS” is the poster child for a drama only growing stronger with age — the Mark Harmon headliner still draws an average of 21.8 million viewers a week in its 11th season and is prepping a possible New Orleans-set spinoff (it already has “NCIS: LA”).

“Criminal Minds,” which will air its 200th episode on Feb. 5, is averaging an impressive 13 million viewers in its ninth season while the network’s oldest series, “CSI” (14 seasons), still draws 12 million viewers a week.

“Grey’s Anatomy” stars Ellen Pompeo and Patrick Dempsey recently signed new two-year deals, increasing the likelihood that the ABC medical drama will reach a 12th season. And with good reason — though it’s no longer the network’s most-watched drama, at an average of 12.7 million viewers it’s just behind “Scandal” (13 million viewers) and “Castle” (12.9 million viewers — it’s getting up there itself at six seasons).

If there’s a secret to keeping a show alive for so many seasons, it seems to be create a family of characters that viewers want to have in their living room year after year, say producers.

“People have really connected with those characters,” says “Criminal Minds” showrunner/executive producer Erica Messer. “And then on top of that, I think that fans tune in every week because of the battle between good and evil — it’s almost that simple. Out of 200 episodes, about 195 of them we’ve stopped the bad guy and there’s been a satisfying end to that week’s journey.”

That ability to neatly tie up each episode with a bow plays into the reason that the longest-running dramas tend to be procedurals, with seemingly limitless cases to help drive stories in the absence of character-based drama.

“The construct that we get to hang all the great character stuff that they give us on a murder every week also gives us that longevity, because this is a procedural,” Nathan says.

“In this weird way it feels endless because the cases every week really are driven by human behavior and there’s a huge spectrum of what that is,” Messer adds. “So I do feel there’s a version of that where this show can just keep on going.”

And while buzz will certainly die down with age, there is a wisdom of experience that can come in handy for the grueling task of churning out 22 episodes season after season.

“One of the advantages about a show that goes for this long is that our crew . . . they work together very well,” says “Bones” creator/executive producer Hart Hanson. “We’re not constantly putting out production fires. The show looks and sounds more expensive than it is because of how good that crew is. It lets us tell more stories.”